Homogeneous Charge Compression Ignition (HCCI) Engines

Contents

Need of HCCI HCCI Engine Concept Advantage & Challenges related to HCCI Future Aspects.

Solution• Hybrid Vehicles• Fuel Cells• HCCI Engines• GDI Engine• Low Emissions Technologies• New Materials• Advanced Design Simulations• Efficient Electronics and Electrical Devices

What is an HCCI Engine?

• HCCI is a form of internal combustion in which the fuel and air are compressed to the point of auto ignition.

• That means no spark is required to ignite the fuel/air mixture

• Creates the same amount of power as a traditional engine, but uses less fuel.

Traditional combustion (left) uses a spark to ignite the mixture. HCCI (right) uses piston compression for a more complete ignition.

How Does It Work?

• A given concentration of fuel and air will spontaneously ignite when it reaches its auto-ignition temperature.

• The concentration/temperature can be controlled several ways:– High compression ratio– Preheating of induction gases– Forced induction– Retaining or reintroducing exhaust

gases

Click here for a nice animation of an HCCI engine in action!

The Challenges Facing Us…

• Emission (NOx & Soot)• Fuel Economy

Fuel Consumption is increased by more than 10 % in last 7 years

Urban Urban PollutionPollution

Traditional combustion (left) uses a spark to ignite the mixture. HCCI (right) uses piston compression for a more complete ignition.

• Unlike 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

SI Engine HCCI

WORKING OF HCCI ENGINE

Comparison with other engines

FOUR STROKE ENGINE

Suction Stroke.

Compression Stroke.

Combustion Stroke.

Exhaust Stroke.

SUCTION STROKE:

Fuel air mixture intake take place.

Compression Stroke: Piston moves from bottom dead centre totop dead centre

COMBUSTION STROKE:

EXHAUST STROKE: Removal of exhaust gases takes place.

Advantages

• Can achieve up to 15% fuel savings

• Lower peak temperature leads to cleaner combustion/lower emissions

• Can use gasoline, diesel, or most alternative fuels

HCCI automobiles could reduce greenhouse gas emissions

POTENTIAL

1. High efficiency, no knock limit on compression ratio..

2. Low PM emissions, no need for PM filter.

3. HCCI provides up to a 15-percent fuel savings, while meeting current emissions standards.

4. HCCI engines can operate on gasoline, diesel fuel, and most alternative fuels.

5. In regards to CI engines, the omission of throttle losses improves HCCI efficiency.

Disadvantages

• Higher cylinder peak pressures may damage the engine

• Auto-ignition is difficult to control

• HCCI Engines have a smaller power range

Prototype HCCI car from Saturn

BARRIERS

1. The auto-ignition 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.

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

3. High HC and CO emissions.

The Future of HCCI

• The future of HCCI looks promising

• Major companies such as GM, Mercedes-Benz, Honda, and Volkswagen have invested in HCCI research.

• Preliminary prototype figures show that HCCI cars can achieve in the area of 43 mpg

HCCI CONCEPT

Starting HCCI engines Charge does not readily auto ignite cold

engines. Early proposal was to start in SI mode

and run in HCCI mode. It involves the risk of knocking and

cylinder failure at high compression ratios.

Now intake air pre-heating with HE and burner system allows startup in HCCI mode with conventional starter.

Control methods of HCCI combustion

The spontaneous and simultaneous combustion of fuel-air mixture need to be controlled.

No direct control methods possible as in SI or CI engines.

Various control methods are:

Variable compression ratio

Variable induction temperature

Variable valve actuation

Control methods of HCCI combustion

Variable compression ratio method

The geometric compression ratio can be changed with a movable plunger at the top of the cylinder head. This concept used in “diesel” model aircraft engine.

Variable induction temperature

The simplest method uses resistance heater to vary inlet temperature. But this method is slow

Now FTM (Fast Thermal Management) is used. It is accomplished by rapidly varying the cycle to cycle intake charge temperature by rapid mixing.

FTM system

Rapid mixing of cool and hot intake air takes place achieving optimal temperature as demanded and hence better control.

Control methods of HCCI combustion Variable valve actuation (VVA)

This method gives finer control within combustion chamber

Involves controlling the effective pressure ratio. It controls the point at which the intake valve closes. If the closure is after BDC, the effective volume and hence compression ratio changes.

Control methods of HCCI combustion

Dual mode transitions

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

This restricts engine operation at high loads

Dual mode transitions Practical HCCI engines will need to

switch to a conventional SI or diesel mode at very low and high load conditions due to dilution limits

Two modes: HCCI-DI dual mode HCCI-SI dual mode

SI mode transitions

It equips VVA and spark ignition system Operates in HCCI mode at low to medium

loads and switches into SI mode at higher loads

Transition is not very stable and smooth

DI-HCCI Long ignition delay and rapid mixing are

required to achieve diluted homogeneous mixture.

Combustion noise and NOx emissions were reduced substantially without an increase in PM.

Combustion phasing is controlled by injection timing.

Thus DI-HCCI proves to be promising alternative for conventional HCCI with good range of operation.

Recent developments in HCCI Turbo charging initially proposed to

increase power Challenges for turbo charging1. Exhaust gas temperatures low (300 to

350 °c) because of high compression ratio.

2. Post turbine exhaust gas temperature must be high enough to preheat intake fuel-air mixture in HE.

3. Low available compressor pressure ratio.

The exhaust has dual effects on HCCI combustion. It dilutes the fresh charge, delaying ignition

and reducing the chemical energy and engine work.

Reduce the CO and HC emissions

Recent developments in HCCI

HCCI prototypes General Motors has demonstrated Opel

Vectra and Saturn Aura with modified HCCI engines.

Mercedes-Benz has developed a prototype engine called Dies Otto, with controlled auto ignition. It was displayed in its F 700 concept car at the 2007 Frankfurt Auto Show

Volkswagen are developing two types of engine for HCCI operation. The first, called Combined Combustion System or CCS, is based on the VW Group 2.0-litre diesel engine but uses homogenous intake charge rather than traditional diesel injection. It requires the use of synthetic fuel to achieve maximum benefit. The second is called Gasoline Compression Ignition or GCI; it uses HCCI when cruising and spark ignition when accelerating. Both engines have been demonstrated in Touran prototypes, and the company expects them to be ready for production in about 2015.

Works Cited• “Homogeneous Charge Compression Ignition”

http://en.wikipedia.org/wiki/Homogeneous_Charge_Compression_Ignition November, 2008.

• “New HCCI Engine” http://videos.howstuffworks.com/multivu/3284-new-hcci-engine-video.htm November, 2008

• “GM Takes New Combustion Technology Out of the Lab and Onto the Road” http://www.gm.com/experience/fuel_economy/news/2007/adv_engines/new-combustion-technology-082707.jsp