HCCI- A New Concept in Engine Combustion

7/30/2019 HCCI- A New Concept in Engine Combustion

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Dept. Of Mechanical Engg, Dr . SMCE, Bengaluru . 2013

ABSTRACT

In the context of environmental restrictions and sustainable development, pollution standards have

become more and more stringent. The design of most fuel efficient and environmental friendly

internal combustion engine so as to meet the future emission standards is currently one of the main

goals of engine researchers. Homogeneous Charge Compression Ignition (HCCI) combustion has the

potential to be highly efficient and to produce low emissions. HCCI engines can have efficiencies as

high as compression-ignition direct-injection (CIDI) engines (an advanced version of the commonly

known diesel engine), while producing ultra-low oxides of nitrogen (NOx) and particulate matter

(PM) emissions. HCCI engines can operate on gasoline, diesel fuel, and most alternative fuels. HCCI

represents the next major step beyond high efficiency CIDI and spark-ignition, direct-injection

(SIDI) engines for use in transportation vehicles. In some regards, HCCI engines incorporate the best

features of both spark ignition (SI) gasoline engines and CIDI engines. Like an SI engine, the charge

is well mixed which minimizes particulate emissions, and like a CIDI engine it is compression

ignited and has no throttling losses, which leads to high efficiency. However, unlike either of these

conventional engines, combustion occurs simultaneously throughout the cylinder volume rather than

in a flame front. This paper reviews the technology involved in HCCI engine, and its merits and

demerits. The challenges encountered and recent developments in HCCI engine are also discussed in

this paper.

CONTENTS


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1 Introduction 1 2 History 3 3 What is HCCI? 5

o Why HCCI? 6 4 Fundamentals & Requirements Of HCCI 6 5 Operation 9

o 5.1 Methods 9o 5.2 Advantages 9o 5.3 Disadvantages 10o 5.4 Control 10

5.4.1 Need for control 10 5.4.2 Variable compression ratio 10 5.4.3 Variable induction temperature 11 5.4.4 Variable exhaust gas percentage 11 5.4.5 Variable valve actuation 11 5.4.6 Variable fuel ignition quality 12 5.4.7 Direct Injection: PCCI or PPCI Combustion 12

o 5.5 High peak pressures and heat release rates 12o 5.6 Power 13o 5.7 Emissions 13o 5.8 Difference from Knock 14o 5.9 Simulation of HCCI Engines 14

6 Prototypes 14 7 Other Applications of HCCI Research 15 8 Challenges For HCCI 15

o 8.1 Controlling Ignition Timing 16o 8.2 Extending The Operating Range 16o 8.3 Cold-Start Capability 17o 8.4 Variable Ignition Timing 17

9 Recent Developments In HCCI 19 10 Conclusion 19 References 20
http://en.wikipedia.org/wiki/Homogeneous_charge_compression_ignition#Introductionhttp://en.wikipedia.org/wiki/Homogeneous_charge_compression_ignition#Historyhttp://en.wikipedia.org/wiki/Homogeneous_charge_compression_ignition#Historyhttp://en.wikipedia.org/wiki/Homogeneous_charge_compression_ignition#Operationhttp://en.wikipedia.org/wiki/Homogeneous_charge_compression_ignition#Methodshttp://en.wikipedia.org/wiki/Homogeneous_charge_compression_ignition#Advantageshttp://en.wikipedia.org/wiki/Homogeneous_charge_compression_ignition#Disadvantageshttp://en.wikipedia.org/wiki/Homogeneous_charge_compression_ignition#Controlhttp://en.wikipedia.org/wiki/Homogeneous_charge_compression_ignition#Controlhttp://en.wikipedia.org/wiki/Homogeneous_charge_compression_ignition#Variable_compression_ratiohttp://en.wikipedia.org/wiki/Homogeneous_charge_compression_ignition#Variable_induction_temperaturehttp://en.wikipedia.org/wiki/Homogeneous_charge_compression_ignition#Variable_exhaust_gas_percentagehttp://en.wikipedia.org/wiki/Homogeneous_charge_compression_ignition#Variable_valve_actuationhttp://en.wikipedia.org/wiki/Homogeneous_charge_compression_ignition#Variable_fuel_ignition_qualityhttp://en.wikipedia.org/wiki/Homogeneous_charge_compression_ignition#Direct_Injection:_PCCI_or_PPCI_Combustionhttp://en.wikipedia.org/wiki/Homogeneous_charge_compression_ignition#High_peak_pressures_and_heat_release_rateshttp://en.wikipedia.org/wiki/Homogeneous_charge_compression_ignition#High_peak_pressures_and_heat_release_rateshttp://en.wikipedia.org/wiki/Homogeneous_charge_compression_ignition#Powerhttp://en.wikipedia.org/wiki/Homogeneous_charge_compression_ignition#Emissionshttp://en.wikipedia.org/wiki/Homogeneous_charge_compression_ignition#Difference_from_Knockhttp://en.wikipedia.org/wiki/Homogeneous_charge_compression_ignition#Simulation_of_HCCI_Engineshttp://en.wikipedia.org/wiki/Homogeneous_charge_compression_ignition#Prototypeshttp://en.wikipedia.org/wiki/Homogeneous_charge_compression_ignition#Other_Applications_of_HCCI_Researchhttp://en.wikipedia.org/wiki/Homogeneous_charge_compression_ignition#Other_Applications_of_HCCI_Researchhttp://en.wikipedia.org/wiki/Homogeneous_charge_compression_ignition#Other_Applications_of_HCCI_Researchhttp://en.wikipedia.org/wiki/Homogeneous_charge_compression_ignition#Prototypeshttp://en.wikipedia.org/wiki/Homogeneous_charge_compression_ignition#Simulation_of_HCCI_Engineshttp://en.wikipedia.org/wiki/Homogeneous_charge_compression_ignition#Difference_from_Knockhttp://en.wikipedia.org/wiki/Homogeneous_charge_compression_ignition#Emissionshttp://en.wikipedia.org/wiki/Homogeneous_charge_compression_ignition#Powerhttp://en.wikipedia.org/wiki/Homogeneous_charge_compression_ignition#High_peak_pressures_and_heat_release_rateshttp://en.wikipedia.org/wiki/Homogeneous_charge_compression_ignition#Direct_Injection:_PCCI_or_PPCI_Combustionhttp://en.wikipedia.org/wiki/Homogeneous_charge_compression_ignition#Variable_fuel_ignition_qualityhttp://en.wikipedia.org/wiki/Homogeneous_charge_compression_ignition#Variable_valve_actuationhttp://en.wikipedia.org/wiki/Homogeneous_charge_compression_ignition#Variable_exhaust_gas_percentagehttp://en.wikipedia.org/wiki/Homogeneous_charge_compression_ignition#Variable_induction_temperaturehttp://en.wikipedia.org/wiki/Homogeneous_charge_compression_ignition#Variable_compression_ratiohttp://en.wikipedia.org/wiki/Homogeneous_charge_compression_ignition#Controlhttp://en.wikipedia.org/wiki/Homogeneous_charge_compression_ignition#Disadvantageshttp://en.wikipedia.org/wiki/Homogeneous_charge_compression_ignition#Advantageshttp://en.wikipedia.org/wiki/Homogeneous_charge_compression_ignition#Methodshttp://en.wikipedia.org/wiki/Homogeneous_charge_compression_ignition#Operationhttp://en.wikipedia.org/wiki/Homogeneous_charge_compression_ignition#Historyhttp://en.wikipedia.org/wiki/Homogeneous_charge_compression_ignition#Introduction


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List of Figures

Fig.1 Side and Frontal views of the Nissan MK 2.5 Liter Engine. 3

Fig.2 Homogeneous Charge Compression Ignition. 5

Fig.3 Shows the concept of HCCI engine. 7

Fig.4 The temperature history in K for is preventative ODT 7simulation. The vertical Axis corresponds to a slice through the

cylinder. Ignition occurs following compression, heating and turbulent mixing.

Fig.5 This pressure trace shows the differences between completely 7homogeneous mixtures and mixtures with small-scale inhomogeneities.

Fig.6 Shows the emission characteristics. 13

Fig.7 shows a relation between Temperature vs Crank Angle & 15

Pressure vs Crank Angle during combustion process of HCCI engine.


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1.INTRODUCTIONEnvironmental protection is a huge growth market for the future. In the years ahead, green

technologies that help improve energy efficiency or reduce emissions will be important growth. With

the advent of increasingly stringent fuel consumption and emissions standards, engine manufacturers

face the challenging task of delivering conventional vehicles that abide by these regulations. HCCI

combustion has the potential to be highly efficient and to produce low emissions. HCCI engines can

have efficiencies as high as compression-ignition, direct-injection (CIDI) engines (an advanced

version of the commonly known diesel engine), while producing ultra-low oxides of nitrogen (NOx)

and particulate matter (PM) emissions. HCCI engines can operate on gasoline, diesel fuel, and most

alternative fuels. While HCCI has been demonstrated and known for quite some time, only the recent

advent of electronic sensors and controls have made HCCI engines a potential practical reality.

HCCI represents the next major step beyond high efficiency CIDI and spark-ignition, direct-

injection (SIDI) engines for use in transportation vehicles. In some regards, HCCI enginesincorporate the best features of both spark ignition (SI) gasoline engines and CIDI engines. Like an

SI engine, the charge is well mixed which minimizes particulate emissions, and like a CIDI engine it

is compression ignited and has no throttling losses, which leads to high efficiency. However, unlike

either of these conventional engines, combustion occurs simultaneously throughout the cylinder

volume rather than in a flame front. HCCI engines have the potential to be lower cost than CIDI

engines because they would likely use a lower pressure fuel-injection system. The emission control

systems for HCCI engines have the potential to be less costly and less dependent on scarce precious

metals than either SI or CIDI engines. HCCI engines might be commercialized in light-duty

passenger vehicles and as much as a half-million barrels of primary oil per day may be saved.

HCCI is potentially applicable to both light and heavy-duty engines. Light-duty HCCI engines can

run on gasoline and have the potential to match or exceed the efficiency of diesel-fuelled CIDI

engines, without the major challenge of NOx and PM emission control or impacting fuel-refining

capability. For heavy-duty vehicles, successful development of the diesel-fuelled HCCI engine is an

important alternative strategy in the event that CIDI engines cannot achieve future NOx and PM

emissions standards.

In fact, HCCI technology could be scaled to virtually every size-class of transportation engines from

small motorcycle to large ship engines. HCCI is also applicable to piston engines used outside the

transportation sector such as those used for electrical power generation and pipeline pumping. HCCIengines are particularly well suited to series hybrid vehicle applications because the engine can be

optimized for operation over a more limited range of speeds and loads compared to primary engines

used with conventional vehicles. Use of HCCI engines in series hybrid vehicles could further

leverage the benefits of HCCI to create highly fuel-efficient vehicles.

Japan and European countries have aggressive research and development (R&D) programs in HCCI,

including both public- and private-sector components. Many of the leading HCCI developments to

date have come from these countries. In fact, two engines are already in production in Japan that use

HCCI during a portion of their operating range: Nissan is producing a light truck engine that uses

intermittent HCCI operation and diesel fuel, and Honda is producing a 2-stroke cycle gasoline engineusing HCCI for motorcycles. HCCI engines cannot be ignored. HCCI combustion is achieved by


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controlling the temperature, pressure, and composition of the fuel and air mixture so that it

spontaneously ignites in the engine. This control system is fundamentally more challenging than

using a spark plug or fuel injector to determine ignition timing as used in SI and CIDI engines,

respectively. The recent advent of electronic engine controls has enabled consideration of HCCI

combustion for application to commercial engines. Even so, several technical barriers must beovercome to make HCCI engines applicable to a wide range of vehicles and viable for high volume

production. Significant challenges include: Controlling Ignition Timing and Burn Rate over a

Range of Engine Speeds and Loads Extending the Operating Range of HCCI to High Engine Loads

Cold-Starts and transient response with HCCI Engines Minimizing Hydrocarbon and Carbon

Monoxide Emissions

Controlling the operation of an HCCI engine over a wide range of speeds and loads is probably the

most difficult hurdle facing HCCI engines. HCCI ignition is determined by the charge mixture

composition, its time-temperature history, and to a lesser extent pressure. Several potential control

methods have been proposed to control HCCI combustion: varying the amount of exhaust gasrecirculation (EGR), using a variable compression ratio (VCR), and using variable valve timing

(VVT) to change the effective compression ratio and/or the amount of hot exhaust gases retained in

the cylinder. VCR and VVT technologies are particularly attractive because their time response

could be made sufficiently fast to handle rapid transients (i.e., accelerations/decelerations). Although

these technologies have shown strong potential, performance is not yet fully proven, and cost and

reliability issues must be addressed.

Although HCCI engines have been demonstrated to operate well at low to medium loads, difficulties

have been encountered at high-load conditions. The combustion process can become very rapid and

intense causing unacceptable noise, potential engine damage, and eventually, unacceptable levels ofNOx emissions. Preliminary research indicates the operating range can be extended significantly by

partially stratifying the fuel/air/residual charge at high loads (mixture and/or temperature

stratification). Several potential mechanisms exist for achieving partial charge stratification,

including: in-cylinder fuel injection, water injection, varying the intake and in-cylinder mixing

processes, and altering in-cylinder flows to vary heat transfer. The extent to which these techniques

can extend the operating range, while preserving HCCI benefits, is currently unknown. Because of

the difficulty of high-load operation, most initial concepts involve switching to traditional SI or CIDI

combustion for operating conditions where HCCI operation is more difficult. This configuration

allows the benefits of HCCI to be realized over a significant portion of the driving cycle but adds thecomplexity of switching the engine between operating modes.

The fundamental processes of HCCI combustion make cold-starts difficult without some

compensating mechanism. Various mechanisms for cold-starting in HCCI mode have been proposed

such as using glow plugs, using a different fuel or fuel additive, and increasing the compression ratio

using VCR or VVT. Spark-ignition may be the most viable approach to cold-start, though it adds

cost and complexity.

HCCI engines have inherently low emissions of NOx and PM but relatively high emissions of

hydrocarbons (HC) and carbon monoxide (CO). Some potential exists to mitigate these emissions atlight load by using direct in-cylinder fuel injection. However, regardless of the ability to minimize


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engine-out HC and CO emissions, controlling HC and CO emissions from HCCI engines will likely

require use of an exhaust emission control device. Catalyst technology for HC and CO removal is

well understood and has been standard equipment on gasoline-fuelled automobiles for 25 years. In

addition, reducing HC and CO emissions from HCCI engines is much easier than reducing NOx and

PM emissions from CIDI engines. However, the cooler exhaust temperatures of HCCI engines mayincrease catalyst light-off time and decrease average effectiveness. Consequently, achieving stringent

future emission standards for HC and CO will likely require some further development of oxidation

catalysts for use with HCCI engines.

Fig.1 Side and Frontal views of the Nissan MK 2.5 Liter Engine.

2.HISTORYHCCI engines have a long history, even though HCCI has not been as widely implemented as spark

ignition or diesel injection. It is essentially an Otto combustion cycle. In fact, HCCI was popular

before electronic spark ignition was used. One example is the hot-bulb engine which used a hot

vaporization chamber to help mix fuel with air. The extra heat combined with compression induced

the conditions for combustion to occur. Homogeneous charge compression ignition (HCCI) engines

have the potential to provide high, diesel-like efficiencies and very low emissions. In an HCCI

engine, a dilute, premixed fuel/air charge auto ignites and burns volumetrically as a result of being

compressed by the piston. The charge is made dilute either by being very lean, or by mixing withrecycled exhaust gases.


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Several technical barriers must be overcome before HCCI can be implemented in production

engines. Variations of HCCI in which the charge mixture and/or temperature are partially stratified

(stratified charge compression ignition or SCCI) have the potential for overcoming many of these

barriers.

Because of HCCI's strong potential, most diesel engine and automobile manufacturers have

established HCCI/SCCI development efforts.

The Sandia HCCI Engine Combustion Fundamentals Laboratory supports this industrial effort. The

laboratory is equipped with two Cummins B-series engines mounted at either end of a double-ended

dynamometer. These production engines have been converted for single-cylinder HCCI/SCCI

operation.

One engine (the so-called all-metal engine) is used to establish operating points, test various fuel

types, develop combustion-control strategies, and investigate emissions.The second engine has extensive optical access for the application of advanced laser diagnostics for

investigations of in-cylinder processes. The design includes an extended piston with piston-crown

window, three large windows near the top of the cylinder wall, and a drop-down cylinder for rapid

cleaning of fouled windows.

The engines are designed to provide a versatile facility for investigations of a wide range of

operating conditions and various fuel-injection, fuel/air/residual mixing, and control strategies that

have the potential of overcoming the technical barriers to HCCI. The size of these engines (0.98

litres/cylinder) was selected so that results are applicable to both automotive and heavy-duty

applications. They are equipped with the following features:

Variable in-cylinder swirl: swirl ratios of 0.9 to 3.2, convertible to swirl ratios up to 7.6.

Multiple fuel systems: fully premixed, port fuel injection, gasoline-type direct-injection, and diesel-

type direct-injection.

Complete intake charge conditioning: simulated or real EGR, intake pressures to 6 atmospheres,

and intake temperatures to 220C. Speeds up to 3600 rpm (metal engine) and 1800 rpm (optical

engine) Variable compression ratio variable through interchangeable pistons (compression ratios

from 12:1 to 21:1 are currently available) Custom HCCI piston design.

Full emissions measurements: CO2, CO, O2, HC, NOx, and smoke

Mechanical valves with a conversion to fully flexible variable valve actuation (VVA) under

development.

Investigations are addressing several issues, including:

Stratification of the fuel/air mixture as a means of improving emissions and combustion efficiency

during part-load operation. The effects of fuel-type on performance and emissions over a range of

speeds and loads Intake pressure boosting for increased power, heat transfer effects, combustion-

phasing control, and extending operation to higher loads.


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Because fuel characteristics are central to HCCI engine design, a variety of fuels are being examined

including gasoline, diesel fuel, and a number of representative constituents of real distillate fuels.

3.WHAT IS HCCI?HCCI is an alternative piston-engine combustion process that can provide efficiencies as high as

compression-ignition, direct-injection (CIDI) engines (an advanced version of the commonly known

diesel engine) while, unlike CIDI engines, producing ultra-low oxides of nitrogen (NOx) and

particulate matter (PM) emissions. HCCI engines operate on the principle of having a dilute,

premixed charge that reacts and burns volumetrically throughout the cylinder as it is compressed by

the piston. In some regards, HCCI incorporates the best features of both spark ignition (SI) and

compression ignition (CI), as shown in Figure 1. As in an SI engine, the charge is well mixed, which

minimizes particulate emissions, and as in a CIDI engine, the charge is compression ignited and has

no throttling losses, which leads to high efficiency. However, unlike either of these conventional

engines, the combustion occurs simultaneously throughout the volume rather than in a flame front.

This important attribute of HCCI allows combustion to occur at much lower temperatures,

dramatically reducing engine-out emissions of NOx.

Most engines employing HCCI to date have dual mode combustion systems in which traditional SI

or CI combustion is used for operating conditions where HCCI operation is more difficult. Typically,

the engine is cold-started as an SI or CIDI engine, then switched to HCCI mode for idle and low- to

mid-load operation to obtain the benefits of HCCI in this regime, which comprises a large portion of

typical automotive driving cycles. For high-load operation, the engine would again be switched to SIor CIDI operation. Research efforts are underway to extend the range of HCCI operation.

Fig.2 Homogeneous Charge Compression Ignition

4.WHYHCCI?


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The modern conventional SI engine fitted with a three-way catalyst can be seen as an very clean

engine. But it suffers from poor part load efficiency. As mentioned earlier this is mainly due to the

throttling. Engines in passenger cars operate most of the time at light- and partload conditions. For

some shorter periods of time, at overtaking and acceleration, they run at high loads, but they seldom

run at high loads for any longer periods. This means that the overall efficiency at normal drivingconditions becomes very low.

The Diesel engine has much higher part load efficiency than the SI engine. Instead the Diesel engine

fights with great smoke and NOx problems. Soot is mainly formed in the fuel rich regions and NOx

in the hot stoichiometric regions. Due to these mechanisms, it is difficult to reduce both smoke and

NOx simultaneously through combustion improvement. Today, there is no well working exhaust

after treatment that takes away both soot and NOx.

The HCCI engine has much higher part load efficiency than the SI engine and comparable to the

Diesel engine, and has no problem with NOx and soot formation like the Diesel engine. In summary,the HCCI engine beats the SI engine regarding the efficiency and the Diesel engine regarding the

emissions.

5.FUNDAMENTALS & REQUIREMENTS OF HCCI

5.1 HCCI Fundamentals

The HCCI PrincipleHCCI means that the fuel and air should be mixed before combustion starts

and that the mixture is auto ignited due to the increase in temperature from the compression stroke.

Thus HCCI is similar to SI in the sense that both engines use a premixed charge and HCCI is similar

to CI as both rely on auto ignition for combustion initiation. However, the combustion process is

totally different for the three types. Figure 4 shows the difference between (a) SI combustion and (b)

HCCI. In the SI engine we have three zones, a burnt zone, an unburned zone and between them a

thin reaction zone where the chemistry takes place. This reaction zone propagates through the

combustion chamber and thus we have flame propagation. Even though the reactions are fast in thereaction zone, the combustion process will take some time as the zone must propagate from spark

plug (zero mass) to the far liner wall (mass wi ). With the HCCI process the entire mass in the

cylinder will react at once. The right part of Figure 4 shows HCCI, or as Onishi called it Active

Thermo-Atmosphere Combustion, ATAC. We see that the entire mass is active but the reaction rate

is low both locally and globally. This means that the combustion process will take some time even if

all the charge is active. The total amount of heat released, Q, will be the same for both processes.

It could be noted that the combustion process can have the same duration even though HCCI

normally has a faster burn rate. Initial tests in Lund on a two stroke engine revealed the fundamental

difference between these two types of engines


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Fig.3 shows the concept of HCCI engine.

Fig.4 The temperature history in K for is preventative ODT simulation. The vertical

Axis corresponds to a slice through the cylinder. Ignition occurs following

compression, heating and turbulent mixing.

Fig.5 this pressure trace shows the differences between completely homogeneous mixtures and

mixtures with small-scale inhomogeneities.

5.2 Requir ements For HCCI


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The HCCI combustion process puts two major requirements on the conditions in the cylinder: (a)

The temperature after compression stroke should equal the auto ignition temperature of the fuel/air

mixture. (b) The mixture should be diluted enough to give reasonable burn rate.

For iso-octane, the auto ignition temperature is roughly 1000K. This means that the temperature inthe cylinder should be 1000 K at the end of the compression stroke where the reactions should start.

This temperature can be reached in two ways, either the temperature in the cylinder at the start of

compression is controlled or the increase in temperature due to compression i.e. compression ratio is

controlled. It

could be interesting to note that the autoignition temperature is a very weak function of air/fuel ratio.

The change in autoignition temperature for iso-octane is only 50K with a factor 2 change in . Figure

7 also shows the normal rich and lean limits found with HCCI. With a too rich mixture the reactivity

of the charge is too high. This means that the burn rate becomes

extremely high with richer mixtures. If an HCCI engine is run too rich the entire charge can beconsumed within a fraction of a crank angle. This gives rise to extreme pressure rise rates and hence

mechanical stress and noise. With a high autoignition temperature like that of natural gas, it is also

possible that formation of NOx can be the load limiting factor. Figure 8 shows the NO formation as a

function of maximum temperature.

Very low emission levels are measured with ethanol. If the combustion starts at a higher temperature

like with natural gas, the temperature after combustion will also be higher for a given amount of heat

released. On the lean side, the temperature increase from the combustion is too low to have complete

combustion. Partial oxidation of fuel to CO can occur at extremely lean mixtures; above 14 has

been tested. However, the oxidation of CO to CO2 requires a temperature of 1400-1500 K. As asummary, HCCI is governed by three temperatures. We need to reach the autoignition temperature to

get things started; the combustion should then increase the temperature to at least 1400 K to have

good combustion efficiency but it should not be increased to more than 1800 K to prevent NO

formation.

6.OPERATION


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6.1Methods

A mixture of fuel and air will ignite when the concentration and temperature of reactants is

sufficiently high. The concentration and/or temperature can be increased by several different ways:Methods

1. High compression ratio

2. Pre-heating of induction gases

3. Forced induction

4. Retained or re-inducted exhaust gases

Once ignited, combustion occurs very quickly. When auto-ignition occurs too early or with too much

chemical energy, combustion is too fast and high in-cylinder pressures can destroy an engine. For

this reason, HCCI is typically operated at lean overall fuel mixtures.

6.2Advantages HCCI provides up to a 30-percent fuel savings, while meeting current emissions standards. Since HCCI engines are fuel-lean, they can operate at a Diesel-like compression ratios (>15),

thus achieving higher efficiencies than conventional spark-ignited gasoline engines.

Homogeneous mixing of fuel and air leads to cleaner combustion and lower emissions.Actually, because peak temperatures are significantly lower than in typical spark ignitedengines, NOxlevels are almost negligible. Additionally, the premixed lean mixture does not

produce soot.

HCCI engines can operate on gasoline, diesel fuel, and most alternative fuels. In regards to gasoline engines, the omission of throttle losses improves HCCI efficiency.6.3 Disadvantages

High in-cylinder peak pressures may cause damage to the engine. High heat release and pressure rise rates contribute to engine wear. The autoignition event is difficult to control, unlike the ignition event in spark ignition (SI)

and diesel engines which are controlled by spark plugs and in-cylinder fuel injectors,respectively.

HCCI engines have a small power range, constrained at low loads by lean flammability limitsand high loads by in-cylinder pressure restrictions.

Carbon monoxide (CO) and hydrocarbon (HC) pre-catalyst emissions are higher than atypical spark ignition engine, caused by incomplete oxidation (due to the rapid combustion

event and low in-cylinder temperatures) and trapped crevice gases, respectively.

6.4 Control
http://en.wikipedia.org/wiki/Nitrogen_oxidehttp://en.wikipedia.org/wiki/Nitrogen_oxidehttp://en.wikipedia.org/wiki/Nitrogen_oxidehttp://en.wikipedia.org/wiki/Soothttp://en.wikipedia.org/wiki/Spark_ignitionhttp://en.wikipedia.org/wiki/Diesel_enginehttp://en.wikipedia.org/wiki/Carbon_monoxidehttp://en.wikipedia.org/wiki/Hydrocarbonhttp://en.wikipedia.org/wiki/Hydrocarbonhttp://en.wikipedia.org/wiki/Carbon_monoxidehttp://en.wikipedia.org/wiki/Diesel_enginehttp://en.wikipedia.org/wiki/Spark_ignitionhttp://en.wikipedia.org/wiki/Soothttp://en.wikipedia.org/wiki/Nitrogen_oxide


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Controlling HCCI is a major hurdle to more widespread commercialization. HCCI is more difficult

to control than other popular modern combustion engines, such as Spark Ignition (SI) and Diesel. In

a typical gasoline engine, a spark is used to ignite the pre-mixed fuel and air. In Diesel engines,

combustion begins when the fuel is injected into compressed air. In both cases, the timing of

combustion is explicitly controlled. In an HCCI engine, however, the homogeneous mixture of fuel

and air is compressed and combustion begins whenever the appropriate conditions are reached. Thismeans that there is no well-defined combustion initiator that can be directly controlled. Engines can

be designed so that the ignition conditions occur at a desirable timing. To achieve dynamic operation

in an HCCI engine, the control system must change the conditions that induce combustion. Thus, the

engine must control either the compression ratio, inducted gas temperature, inducted gas pressure,

fuel-air ratio, or quantity of retained or re-inducted exhaust. Several control approaches are discussed

below.

6.4.1 The Need For Control

For better understanding of the combustion process, laser diagnostics is needed and this knowledge

can be used to optimize the system. However, the HCCI process is very sensitive to disturbances. It

can be sufficient to change the inlet temperature 2C to move from a very good operating point to a

total misfire. This sensitivity makes the HCCI engine require closed loop combustion control, CLCC.

Closed loop control requires as always a sensor, control algorithm and control means. The main

parameter to control for HCCI is the combustion timing i.e. when in the cycle combustion

takes place. Figure 17 shows the rate of heat release for a range of timings. With early phasing the

rate of heat release is higher and as it is phased later the burn rate goes down. With combustion

before top dead centre, TDC, the temperature will be increased both by the chemical reactions and

the compression due to piston motion. Thus for a given auto ignition temperature, combustion onset

before TDC will result in faster reactions. With the conditions changed to give combustion onset

close to TDC, the temperature will not be increased by piston motion, the only temperature

driver would be the chemical reactions. This gives a more sensitive system and the later the

combustion phasing the more sensitive the system is. This is the underlying problem with HCCI

combustion control. We want a late combustion phasing to reduce burn rate and hence pressure rise

rate and peak pressure but on the other hand we cannot accept too much variations in

the combustion process. How late we can go depends on the quality of the control system. With a

fast and accurate control system we can go later and hence reduce the noise and mechanical loads of

the engine.

6.4.2 Var iable compression ratio

There are several methods for modulating both the geometric and effective compression ratio. The

geometric compression ratio can be changed with a movable plunger at the top of the cylinder head.

This is the system used in "diesel" model aircraft engines. The effective compression ratio can be

reduced from the geometric ratio by closing the intake valve either very late or very early with some

form of variable valve actuation (i.e. variable valve timingpermitting Miller cycle). Both of the

approaches mentioned above require some amounts of energy to achieve fast responses.

Additionally, implementation is expensive. Control of an HCCI engine using variable compression
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ratio strategies has been shown effective.[8]The effect of compression ratio on HCCI combustion has

also been studied extensively.[9]

6.4.3Variable induction temperature

In HCCI engines, the autoignition event is highly sensitive to temperature. Various methods have

been developed which use temperature to control combustion timing. The simplest method uses

resistance heaters to vary the inlet temperature, but this approach is slow (cannot change on a cycle-

to-cycle basis).[10]Another technique is known as fast thermal management (FTM). It is

accomplished by rapidly varying the cycle to cycle intake charge temperature by rapidly mixing hot

and cold air streams.[11]It is also expensive to implement and has limited bandwidth associated with

actuator energy.

6.4.4 Variable exhaust gas percentage

Exhaust gas can be very hot if retained or re-inducted from the previous combustion cycle or cool if

recirculated through the intake as in conventional EGRsystems. The exhaust has dual effects on

HCCI combustion. It dilutes the fresh charge, delaying ignition and reducing the chemical energy

and engine work. Hot combustion products conversely will increase the temperature of the gases in

the cylinder and advance ignition. Control of combustion timing HCCI engines using EGR has been

shown experimentally.[12]

6.4.5 Var iable valve actuati on

Variable valve actuation (VVA) has been proven to extend the HCCI operating region by giving

finer control over the temperature-pressure-time history within the combustion chamber. VVA can

achieve this via two distinct methods:

Controlling the effective compression ratio: A variable duration VVA system on intake cancontrol the point at which the intake valve closes. If this is retarded past bottom dead center

(BDC), then the compression ratio will change, altering the in-cylinder pressure-time history

prior to combustion. Controlling the amount of hot exhaust gas retained in the combustion chamber: A VVA

system can be used to control the amount of hot internal exhaust gas recirculation (EGR)

within the combustion chamber. This can be achieved with several methods, including valve

re-opening and changes in valve overlap. By balancing the percentage of cooled external

EGR with the hot internal EGR generated by a VVA system, it may be possible to control the

in-cylinder temperature.

While electro-hydraulic and camless VVA systems can be used to give a great deal of control over

the valve event, the componentry for such systems is currently complicated and expensive.

Mechanical variable lift and duration systems, however, although still being more complex than a

standard valvetrain, are far cheaper and less complicated. If the desired VVA characteristic is known,
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then it is relatively simple to configure such systems to achieve the necessary control over the valve

lift curve. Also see variable valve timing.

6.4.6 Variable fuel igniti on quality

Another means to extend the operating range is to control the onset of ignition and the heat release

rate[13][14]by manipulating the fuel itself. This is usually carried out by adopting multiple fuels and

blending them "on the fly" for the same engine.[15]Examples could be blending of commercial

gasoline and diesel fuels,[16]adopting natural gas[17]or ethanol ".[18]This can be achieved in a

number of ways;

Blending fuels upstream of the engine: Two fuels are mixed in the liquid phase, one with lowresistance to ignition (such as diesel fuel) and a second with a greater resistance (gasoline),

the timing of ignition is controlled by varying the compositional ratio of these fuels. Fuel is

then delivered using either a port or direct injection event. Having two fuel circuits: Fuel A can be injected in the intake duct (port injection) and Fuel B

using a direct injection (in-cylinder) event, the proportion of these fuels can be used to

control ignition, heat release rate as well as exhaust gas emissions.

6.4.7 Direct In jection: PCCI or PPCI Combustion

Compression Ignition Direct Injection (CIDI) combustion is a well-established means of controlling

ignition timing and heat release rate and is adopted in diesel engine combustion. Partially Pre-mixed

Charge Compression Ignition (PPCI) also known as Premixed Charge Compression Ignition (PCCI)

is a compromise between achieving the control of CIDI combustion but with the exhaust gas

emissions of HCCI, specifically soot.[19]On a fundamental level, this means that the heat release rate

is controlled preparing the combustible mixture in such a way that combustion occurs over a longer

time duration and is less prone to knocking. This is done by timing the injection event such that the

combustible mixture has a wider range of air/fuel ratios at the point of ignition, thus ignition occurs

in different regions of the combustion chamber at different times - slowing the heat release rate.

Furthermore this mixture is prepared such that when combustion occurs there are fewer rich pockets

thus reducing the tendency for soot formation.[20]The adoption of high EGR and adoption of diesel

fuels with a greater resistance to ignition (more "gasoline like") enables longer mixing times prior to

ignition and thus fewer rich pockets thus resulting in the possibility of both lower soot emissions andNox.

6.5 H igh Peak Pressur es and Heat Release Rates

In a typical gasoline or diesel engine, combustion occurs via a flame. Hence at any point in time,

only a fraction of the total fuel is burning. This results in low peak pressures and low energy release

rates. In HCCI, however, the entire fuel/air mixture ignites and burns nearly simultaneously resulting

in high peak pressures and high energy release rates. To withstand the higher pressures, the engine

has to be structurally stronger and therefore heavier. Several strategies have been proposed to lowerthe rate of combustion. Two different fuels, with different autoignition properties, can be used to
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lower the combustion speed.[21]However, this requires significant infrastructure to implement.

Another approach uses dilution (i.e. with exhaust gases) to reduce the pressure and combustion rates

at the cost of work production.[22]

6.6 Power

In both a spark ignition engine and diesel engine, power can be increased by introducing more fuel

into the combustion chamber. These engines can withstand a boost in power because the heat release

rate in these engines is slow. However, in HCCI engines the entire mixture burns nearly

simultaneously. Increasing the fuel/air ratio will result in even higher peak pressures and heat release

rates. In addition, many of the viable control strategies for HCCI require thermal preheating of the

charge which reduces the density and hence the mass of the air/fuel charge in the combustion

chamber, reducing power. These factors make increasing the power in HCCI engines challenging.

One way to increase power is to use fuels with different autoignitionproperties. This will lower theheat release rate and peak pressures and will make it possible to increase the equivalence ratio.

Another way is to thermally stratify the charge so that different points in the compressed charge will

have different temperatures and will burn at different times lowering the heat release rate making it

possible to increase power.[23]A third way is to run the engine in HCCI mode only at part load

conditions and run it as a diesel or spark ignition engine at full or near full load conditions .[24]Sincemuch more research is required to successfully implement thermal stratification in the compressed

charge, the last approach is being studied more intensively.

6.7 Emissions

Because HCCI operates on lean mixtures, the peak temperatures are lower in comparison to spark

ignition (SI) and Diesel engines. The low peak temperatures prevent the formation of NOx. This

leads to NOx emissions at levels far less than those found in traditional engines. However, the low

peak temperatures also lead to incomplete burning of fuel, especially near the walls of the

combustion chamber. This leads to high carbon monoxide and hydrocarbon emissions. An oxidizing

catalyst would be effective at removing the regulated species because the exhaust is still oxygen rich.

Fig.6 shows the emission characteristics.
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6.9Simulation of HCCI Engines

The development of computational models for simulating combustion and heat release rates of HCCI

engines has required the advancement of detailed chemistry models.[16][25][26]This is largely becauseignition is most sensitive to chemical kinetics rather than turbulence/spray or spark processes as are

typical in direct injection compression ignition or spark ignition engines. Computational models have

demonstrated the importance of accounting for the fact that the in-cylinder mixture is actually in-

homogeneous, particularly in terms of temperature. This in-homogeneity is driven by turbulent

mixing and heat transfer from the combustion chamber walls, the amount of temperature

stratification dictates the rate of heat release and thus tendency to knock.[27]This limits the

applicability of considering the in-cylinder mixture as a single zone resulting in the uptake of 3D

computational fluid dynamics codes such as Los Alamos National Laboratory's KIVA CFD code and

faster solving probability density function modelling codes.

7. 6.8Di ff erence fr om Knock8. Engine knock or pinging occurs when some of the unburnt gases ahead of the flame in a

spark ignited engine spontaneously ignite. The unburnt gas ahead of the flame is compressed

as the flame propagates and the pressure in the combustion chamber rises. The high pressure

and corresponding high temperature of unburnt reactants can cause them to spontaneously

ignite. This causes a shock wave to traverse from the end gas region and an expansion wave

to traverse into the end gas region. The two waves reflect off the boundaries of the

combustion chamber and interact to produce high amplitude standing waves.

9. A similar ignition process occurs in HCCI. However, rather than part of the reactant mixturebeing ignited by compression ahead of a flame front, ignition in HCCI engines occurs due topiston compression. In HCCI, the entire reactant mixture ignites (nearly) simultaneously.

Since there are very little or no pressure differences between the different regions of the gas,

there is no shock wave propagation and hence no knocking. However, at high loads (i.e. high

fuel/air ratios), knocking is a possibility even in HCCI.

7PROTOTYPESAs of 2012, there were no HCCI engines being produced in commercial scale. However, several car

manufacturers have fully functioning HCCI prototypes.

In 2007-2009, General Motors has demonstrated HCCI with a modified 2.2 L Family IIengine installed in Opel Vectra and Saturn Aura,.[30][31][32]The engine operates in HCCI

mode at speeds below 60 miles per hour (97 km/h) or when cruising, switching to

conventional spark-ignition when the throttle is opened, and produces fuel economy of

43 miles per imperial gallon (6.6 L/100 km; 36 mpg-US) and carbon dioxide emissions of

about 150 grams per kilometer, improving on 37 miles per imperial gallon (7.6 L/100 km;

31 mpg-US) and 180 g/km of the conventional 2.2 L direct injection version.[33]GM is also

researching smallerFamily 0 engines for HCCI applications. GM has used KIVA in the

development of direct-injection, stratified charge gasoline engines as well as the fast burn,homogeneous-charge gasoline engine.[29]
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Mercedes-Benz has developed a prototype engine called DiesOtto, with controlled autoignition. It was displayed in its F 700 concept car at the 2007 Frankfurt Auto Show.[34]

Volkswagen are developing two types of engine for HCCI operation. The first, calledCombined Combustion System orCCS, is based on the VW Group 2.0-litre diesel engine but

uses homogeneous intake charge rather than traditional diesel injection. It requires the use of

synthetic fuel to achieve maximum benefit. The second is called Gasoline CompressionIgnition orGCI; it uses HCCI when cruising and spark ignition when accelerating. Both

engines have been demonstrated in Touranprototypes, and the company expects them to be

ready for production in about 2015.[35][36]

In October 2005, the Wall Street Journal reported that Honda was developing an HCCIengine as part of an effort to produce a next generation hybrid car.[37]

Oxy-Gen Combustion, a UK-based Clean Technology company, has produced a full-loadHCCI concept engine with the aid of Michelin and Shell [2]

8OTHER APPLICATIONS OF HCCI RESEARCH

To date, there have been few prototype engines running in HCCI mode; however, the research efforts

invested into HCCI research have resulted in direct advancements in fuel and engine development.

Examples include:

PCCI/PPCI combustion - A hybrid of HCCI and conventional diesel combustion offeringmore control over ignition and heat release rates with lower soot and NOx emissions.

Advancements in fuel modelling - HCCI combustion is driven mainly by chemical kineticsrather than turbulent mixing or injection, reducing the complexity of simulating the chemistry

which results in fuel oxidation and emissions formation. This has led to increasing interest

and development of chemical kinetics which describe hydrocarbon oxidation.

Fuel blending applications - Due to the advancements in fuel modelling, it is now possible tocarry out detailed simulations of hydrocarbon fuel oxidation, enabling simulations of

practical fuels such as gasoline/diesel and ethanol. Engineers can now blend fuels virtually

and determine how they will perform in an engine context.

9 CHALLENGES FOR HCCICombustion is achieved by controlling the temperature, pressure and composition of the air/fuel

mixture so that it auto ignites near top dead centre (TDC) as it is compressed by the piston. This

mode of ignition is fundamentally more challenging than using a direct control mechanism such as a

spark plug or fuel injector to dictate ignition timing as in SI and CIDI engines, respectively. While

HCCI has been known for some twenty years, it is only with the recent advent of electronic engine

controls that HCCI combustion can be considered for application to commercial engines. Even so,

several technical barriers must be overcome before HCCI engines will be viable for high-volume
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production and application to a wide range of vehicles. The following describes the more significant

challenges for developing practical HCCI engines for transportation. Greater detail regarding these

technical barriers, potential solutions, and the R&D needed to overcome them are provided in this

section. Some of these issues could be mitigated or eliminated if the HCCI engine was used in a

series hybrid-electric application, as discussed above.

Fig.7 shows a relation between Temperature vs Crank Angle & Pressure vs Crank Angle

during combustion process of HCCI engine.

9.1 Controll ing I gnition Timingover a Range of Speeds and Loads Expanding the controlled

operation of an HCCI engine over a wide range of speeds and loads is probably the most difficult

hurdle facing HCCI engines. HCCI ignition is determined by the charge mixture composition and its

temperature history (and to a lesser extent, its pressure history). Changing the power output of an

HCCI engine requires a change in the fuelling rate and, hence, the charge mixture. As a result, the

temperature history must be adjusted to maintain proper combustion timing. Similarly, changing the

engine speed changes the amount of time for the auto ignition chemistry to occur relative to the

piston motion. Again, the temperature history of the mixture must be adjusted to compensate. These

control issues become particularly challenging during rapid transients. Several potential control

methods have been proposed to provide the compensation required for changes in speed and load.

Some of the most promising include varying the amount of hot EGR introduced into the incoming

charge, using a VCR mechanism to alter TDC temperatures, and using VVT to change the effective

compression ratio and/or the amount of hot residual retained in the cylinder. VCR and VVT areparticularly attractive because their time response could be made sufficiently fast to handle rapid

transients. Although these techniques have shown strong potential, they are not yet fully proven, and

cost and reliability issues must be addressed.

9.2 Extending the Operating Rangeto High Loads Although HCCI engines have been demonstrated

to operate well at low-to-medium loads, difficulties have been encountered at high-loads.

Combustion can become very rapid and intense, causing unacceptable noise, potential engine

damage, and eventually unacceptable levels of NOx emissions. Preliminary research indicates theoperating range can be extended significantly by partially stratifying the charge (temperature and


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mixture stratification) at high loads to stretch out the heat- release event. Several potential

mechanisms exist for achieving partial charge stratification, including varying in-cylinder fuel

injection, injecting water, varying the intake and in-cylinder mixing processes to obtain non-uniform

fuel/air/residual mixtures, and altering cylinder flows to vary heat transfer. The extent to which these

techniques can extend the operating range is currently unknown and R&D will be required. Becauseof the difficulty of high-load operation, most initial concepts involve switching to traditional SI or CI

combustion for operating conditions where HCCI operation is more difficult. This dual mode

operation provides the benefits of HCCI over a significant portion of the driving cycle but adds to the

complexity by switching the engine between operating modes.

9.3 Cold-Start Capabil ityAt cold start, the compressed-gas temperature in an HCCI engine will be

reduced because the charge receives no preheating from the intake manifold and the compressed

charge is rapidly cooled by heat transferred to the cold combustion chamber walls. Without some

compensating mechanism, the low compressed-charge temperatures could prevent an HCCI engine

from firing. Various mechanisms for cold-starting in HCCI mode have been proposed, such as using

glow plugs, using a different fuel or fuel additive, and increasing the compression ratio using VCR or

VVT. Perhaps the most practical approach would be to start the engine in spark-ignition mode and

transition to HCCI mode after warm-up. For engines equipped with VVT, it may be possible to make

this warm- up period as short as a few fired cycles, since high levels of hot residual gases could be

retained from previous spark-ignited cycles to induce HCCI combustion. Although solutions appear

feasible, significant R&D will be required to advance these concepts and prepare them for

production engines. 4. Hydrocarbon and Carbon Monoxide Emissions HCCI engines have inherently

low emissions of NOx and PM, but relatively high emissions of hydrocarbons (HC) and carbonmonoxide (CO). Some potential exists to mitigate these emissions at light load by using direct in-

cylinder fuel injection to achieve appropriate partial-charge stratification. However, in most cases,

controlling HC and CO emissions from HCCI engines will require exhaust emission control devices.

Catalyst technology for HC and CO removal is well understood and has been standard equipment on

automobiles for many years. However, the cooler exhaust temperatures of HCCI engines may

increase catalyst light-off time and decrease average effectiveness. As a result, meeting future

emission standards for HC and CO will likely require further development of oxidation catalysts for

low-temperature exhaust streams. However, HC and CO emission control devices are simpler, more

durable, and less dependent on scarce, expensive precious metals than are NOx and PM emissioncontrol devices. Thus, simultaneous chemical oxidation of HC and CO (in an HCCI engine) is much

easier than simultaneous chemical reduction of NOx and oxidation of PM (in a CIDI engine). In

addition, HC and CO emission control devices are simpler, more durable, and less dependent on

scarce, expensive precious metals.

9.4Var iable CompressionIgnition There are several methods of modulating both the geometric and

effective compression ratio. The geometric compression ratio can be changed with a movable

plunger at the top of the cylinder head. The effective compression ratio can be reduced from thegeometric ratio by closing the intake valve either very late or very early with some form of variable


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valve actuation (i.e. variable valve timing permitting Miller cycle). Both of the approaches

mentioned above require some amounts of energy to achieve fast responses and are expensive (no

more true for the 2nd solution, the variable valve timing being now maitrized). A 3rd proposed

solution is being developed by the MCE-5 society (new rod).

Mil ler cycle:

In engineering, the Miller cycle is a combustion process used in a type of four-stroke internal

combustion engine. The Miller cycle was patented by Ralph Miller, an American engineer, in the

1940s. This type of engine was first used in ships and stationary power-generating plant, but has

recently (late 1990s) been adapted by Mazda for use in their Millenia large sedan. The traditional

Otto cycle used four "strokes", of which two can be considered "high power" the compression and

power strokes. Much of the power lost in an engine is due to the energy needed to compress the

charge during the compression stroke, so systems to reduce this can lead to greater efficiency.

In the Miller cycle the intake valve is left open longer than it normally would be. This is the "fifth"

cycle that the Miller cycle introduces. As the piston moves back up in what is normally the

compression stroke, the charge is being pushed back out the normally closed valve. Typically this

would lead to losing some of the needed charge, but in the Miller cycle the piston in fact is over-fed

with charge from a supercharger, so blowing a bit back out is entirely planned. The supercharger

typically will need to be of the positive displacement kind (due its ability to produce boost at

relatively low RPM) otherwise low-rpm torque will suffer. The key is that the valve only closes, and

compression stroke actually starts, only when the piston has pushed out this "extra" charge, say 20 to

30% of the overall motion of the piston. In other words the compression stroke is only 70 to 80% aslong as the physical motion of the piston. The piston gets all the compression for 70% of the work.

The Miller cycle "works" as long as the supercharger can compress the charge for less energy than

the piston. In general this is not the case, at higher amounts of compression the piston is much better

at it. The key, however, is that at low amounts of compression the supercharger is more efficient than

the piston. Thus the Miller cycle uses the supercharger for the portion of the compression where it is

best, and the piston for the portion where it is best. All in all this leads to a reduction in the power

needed to run the engine by 10 to 15%. To this end successful production versions of this cycle have

typically used variable valve timing to "switch on & off" the Miller cycle when efficiency does not

meet expectation. In a typical Spark Ignition Engine however the Miller cycle yields another benefit.

Compression of air by the supercharger and cooled by an intercooler will yield a lower intake charge

temperature than that obtained by a higher compression. This allows ignition timing to be altered to

beyond what is normally allowed before the onset of detonation, thus increasing the overall

efficiency still further. A similar delayed valve closing is used in some modern versions of Atkinson

cycle engines, but without the supercharging.


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10. RECENT DEVELOPMENTS IN HCCIThere has been an exhaustive literature search of worldwide R&D on HCCI. Table 1 shows a

summary of recent developments in HCCI technology. In addition, Ford, General Motors (GM), and

Cummins Engine Company have been performing research on HCCI combustion. Ford motor

company has an active research program in HCCI combustion. Researchers are using optical

diagnostics in single-cylinder engines to explore viable HCCI operating regimes and to investigate

methods of combustion control. In addition, chemical kinetic and cycle simulation models are being

applied to better understand the fundamentals of the HCCI process and to explore methods of

implementing HCCI technology. GM at a research level is evaluating the potential for incorporating

HCCI combustion into engine systems. This work includes assessing the strengths and weaknesses of

HCCI operation relative to other advanced concepts, assessing how best to integrate HCCI

combustion into a viable powertrain, and the development of appropriate modelling tools. Work is

focused on fuels, combustion control, combustion modelling, and mode transitioning between HCCI

and traditional SI or CI combustion. GM is also supporting HCCI work at the university level.

Cummins has been researching HCCI for almost 15 years. Industrial engines run in-house using

HCCI combustion of natural gas have achieved remarkable emission and efficiency results.

However, Cummins has found that it is quite challenging to control the combustion phasing over a

real-world operating envelope including variations in ambient conditions, fuel quality variation,

speed and load. Because the new diesel emissions targets are beyond the capability of conventional

diesel engines, Cummins is investigating all options, including HCCI, as part of their design palette

and future engine strategy.

11. CONCLUSION

A high-efficiency, gasoline-fuelled HCCI engine represents a major step beyond SIDI engines for

light-duty vehicles. HCCI engines have the potential to match or exceed the efficiency of diesel-

fuelled CIDI engines without the major challenge of NOx and PM emission control or a major

impact on fuel-refining capability. Also, HCCI engines would probably cost less than CIDI engines

because HCCI engines would likely use lower-pressure fuel-injection equipment, and the combustion

characteristics of HCCI would potentially enable the use of emission control devices that depend less

on scarce and expensive precious metals. In addition, for heavy-duty vehicles, successful

development of the diesel- fuelled HCCI engine is an important alternative strategy in the event that

CIDI engines cannot achieve future NOx and PM emissions standards.

12. REFERENCES


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1. Najt, P. M. and Foster, D. E., "Compression- Ignited Homogeneous Charge Combustion," SAE

paper 830264, 1983.

2. Noguchi, M., Tanaka, Y., Tanaka, T., and Takeuchi, Y., "A Study on Gasoline Engine

Combustion by Observation of Intermediate Reactive Products During Combustion," SAE paper

790840, 1979.

3. Iida, N., "Alternative Fuels and Homogeneous Charge Compression Ignition Combustion

Technology," SAE paper 972071, 1997.

4. Aceves, S. M., Flowers, D. L., Westbrook, C. K., Smith, J. R., Pitz, W., Dibble, R., Christensen,

M., and Johansson, B., "A Multi-Zone Model for Prediction of HCCI Combustion and Emissions,"

SAE paper no. 2000- 01-0327, 2000.

5. Kelly-Zion, P. L., and Dec, J. E. "A Computational Study of the Effect of Fuel Type on Ignition

Time in HCCI Engines," accepted for presentation at and publication in the proceedings of the 2000

International Combustion Symposium.

6. Christensen M., Hultqvist, A. and Johansson, B., "Demonstrating the Multi-Fuel Capability of a

Homogeneous Charge Compression Ignition Engine with Variable Compression Ratio," SAE Paper,

No. 1999-01-3679, 1999.

7. Flynn P. et al., "Premixed Charge Compression Ignition Engine with Optimal CombustionControl," International Patent WO9942718, World Intellectual Property Organization.

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HCCI- A New Concept in Engine Combustion