Advanced combustion methods for simultaneous reduction of emissions and fuel consumption of compression ignition engines

7/23/2019 Advanced combustion methods for simultaneous reduction of emissions and fuel consumption of compression igni

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O R I G I N A L P A P E R

Advanced combustion methods for simultaneous reductionof emissions and fuel consumption of compression ignition engines

P. Brijesh A. Chowdhury S. Sreedhara

Received: 25 February 2014 / Accepted: 27 June 2014 / Published online: 16 July 2014

Springer-Verlag Berlin Heidelberg 2014

Abstract In this work, advanced combustion modes i.e.

improved low-temperature combustion (LTC) and reac-tivity controlled compression ignition (RCCI) have been

achieved in a diesel engine. LTC mode has been improved

using oxidized EGR (OEGR). Studies were carried out for

a pre-optimized set of operating parameters of the engine.

Reduction in NOx and PM, improved LTC, was achieved

with higher OEGR percentages. Higher concentrations of

CO2 and lower concentrations of reacting species with

increased OEGR created higher ignition delays, and hence,

lower PM. Results also showed the importance of catalytic

converter in reduction of tail-pipe HC, CO and PM. RCCI

has been achieved using fuels with different reactivities.

Liquefied petroleum gas (LPG) with low reactivity was

inducted along with air, and diesel with high reactivity was

injected into the cylinder. Percentage of LPG was varied

from 0 to 40 % with step size of 10 %. Results showed that

PM, NOx and CO were reduced with increased LPG. Due

to the possibility of a minor amount of LPG-air mixture

being trapped in crevices during the compression stroke,

HC was increased and BTE was decreased with increased

LPG percentage. The results indicate that RCCI achieved

with lower amount of LPG (*10 %) is more beneficial for

the reduction of PM, NOx and CO with acceptable change

in values of HC and BTE. A reduction in premixed heat

release peak and minor increase in ignition delays were

observed with increased LPG percentage. It indicates that

LPG slows down the reaction rate during premixed

combustion.

Keywords Compression ignition engine

Low-temperature combustion Oxidized EGR Reactivitycontrolled compression ignition Liquefied petroleum gas

Emissions

Introduction

Although diesel engines are more favourable for their

efficiencies over the gasoline engines, the trade-off

between NOx and PM remains a major dilemma. The

adverse impact on human health due to NOx and PM is

increasing rapidly in the metropolitan areas (Ilyas et al.

2010). Hence, legislative bodies impose stringent regula-

tions on these emissions. As a result, various diesel engine

emission control techniques were developed and imple-

mented in diesel vehicles to meet the new regulations

(Bauner et al.2009; Brijesh and Sreedhara2013). NOxcan

be reduced by reducing the peak temperature during

combustion, but PM increases with lower temperatures

(Hill and Smoot 2000; Heywood 1988). In contrast, soot

formation may be reduced by improving homogeneity of

fuelair mixture with equivalence ratios less than one

(Pickett and Siebers2004). Modern combustion techniques

such as premixed charge compression ignition (PCCI),

low-temperature combustion (LTC), homogeneous charge

compression ignition (HCCI), reactivity controlled com-

pression ignition (RCCI), etc. offer promising solutions for

simultaneous reduction of NOxand PM (Dec2009; Brijesh

and Sreedhara2013).

Experimental and numerical studies show that various

parameters such as exhaust gas recirculation (EGR),

compression ratio (CR), spray parameters, airfuel ratio.

etc. play an important role in modern combustion tech-

niques (Brijesh and Sreedhara 2013; Brijesh et al. 2014b;

P. Brijesh (&) A. Chowdhury S. SreedharaI.C. Engines and Combustion Lab, Indian Institute of

Technology Bombay, Mumbai 400076, India

e-mail: [email protected]

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Clean Techn Environ Policy (2015) 17:615625

DOI 10.1007/s10098-014-0811-y


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Dec2009; Kook et al. 2005; Dec et al. 2009; Asad et al.

2008; Brijesh et al. 2013, 2014a). Brijesh et al. (Brijesh

et al. 2013, 2014a) have studied the influence of various

factors on performance, emissions and combustion

parameters. They have achieved LTC mode of combustion

by the combination of retarded injection timing and mod-

erate rate of ultra-cooled EGR (UCEGR). Results indicated

significant reductions in NOx (*90 %) and PM (*50 %)with considerable improvement in brake thermal efficiency

(*12 %) with the optimized operating conditions (Brijesh

et al. 2013). However, the effect of LTC on CO and HC

emissions was found to be insignificant.

Various studies demonstrate the possibility of

improvement in NOx-PM trade-off with treated EGR

(Maiboom et al.2008; Zheng et al. 2004; Fernandez et al.

2009). Improvement in NOx-PM trade-off had been

observed by Maiboom et al. (Maiboom et al. 2008) with

supplemental cooled EGR. Fernandez et al. (Fernandez

et al. 2009) have also achieved simultaneous reduction in

NOx and PM with a minimum penalty in fuel economythrough reformed EGR. Literature also show that reformed

EGR helped in stabilization of the combustion process

(Zheng et al.2002,2007; Asad and Zheng2008). Catalytic

oxidation of exhaust gases in the high-pressure EGR loop

reduced the recycled combustibles, resulting in significant

stabilization of the cycle variations, thereby extending the

limits of EGR applicability (Zheng et al.2002,2007; Asad

and Zheng2008). The effect of treated EGR on the engine

operational stabilities and emissions was investigated by

Asad and Zheng (Asad and Zheng 2008). Results of their

study showed that stabilized LTC mode was achieved

using catalytic EGR (CEGR).

Reduction in NOx and PM can also be achieved with

RCCI mode of operation in diesel engines. Numerous

studies have been carried out to achieve RCCI in diesel

engines (Kokjohn et al. 2009; Pohlkamp and Reitz 2012;

Taniguchi et al. 2012; Dempsey and Reitz 2011; Splitter

et al.2012; Lata et al.2011; Nieman et al.2012). RCCI had

been achieved using fuels with different reactivities. It was

observed that fuel blending creates reactivity gradient in

the cylinder, resulting reduced rate of pressure rise com-

pared to single fuel premixed combustion. Kokjohn et al.

(Kokjohn et al. 2009) had achieved RCCI by injecting

gasoline fuel into the port and diesel fuel directly in the

cylinder. During their study, improvement in efficiencies,

while maintaining low NOx and PM, had been observed.

Pohlkamp and Reitz (Pohlkamp and Reitz 2012) have

realized RCCI mode of combustion with split early direct-

injected diesel fuel and port-fuel-injected gasoline for a

wide operating range. Results indicated that RCCI reduces

NOxand soot, but increases HC and CO emissions. Similar

results were also observed by Taniguchi et al. (Taniguchi

et al.2012). Reduction in PM was observed for a dual fuel

engine running with natural gas and diesel fuel. A signifi-

cant reduction in smoke with introduction of LPG

(*50 %) along with air was also observed by Nazar et al.

(Nazar et al. 2006) during their study with a bio-diesel-

fuelled diesel engine. By carrying out a study on RCCI

operation, Nieman et al. (Nieman et al. 2012) concluded

that due to lower reactivity, natural gas is a better fuel than

gasoline to achieve RCCI mode of combustion. The ana-lysis carried out by Thompson et al. (Thompson et al.

2009) indicates that significant reduction in air pollutant

could be achieved using natural gas as a fuel for on-road

vehicles.

In this work, improved LTC has been achieved with the

help of oxidized EGR (OEGR). Experimental investigation

has also been carried out to achieve RCCI using liquefied

petroleum gas (LPG) fuel. The effect of LPG on engine

performance and emissions has been studied too.

Experimental test rig

A schematic of the experimental setup is shown in Fig. 1.

The test rig consists of a variable compression ratio (VCR)

diesel engine connected with a water-cooled eddy current

dynamometer. An in-cylinder pressure transducer and a

crank angle encoder are mounted with the engine to obtain

p-h diagram. A Labview-based software, ICEngineSoft,

was used to calculate heat release rate (HRR), indicated

mean effective pressure (IMEP), etc. from thep-hdiagram.

Essential instrumentation for measuring air flow rate, diesel

and LPG fuel flow rates, fuel line pressure, temperature at

various locations and load is also integrated into the test

rig. A data acquisition system, NI USB-6210, is provided

for acquiring various relevant parameters from the instru-

ments. Details of instruments are tabulated in Table 1.

Details of the test engine

A single cylinder, four-stroke, direct injection (DI), VCR

diesel engine has been used for this work. The specifica-

tions of the test engine are given in Table 2. The engine has

been converted into diesel dual fuel (DDF) engine by

providing a facility to introduce LPG into the intakemanifold. Table3 shows the specifications of diesel and

LPG fuel injection system.

Details of the LPG and EGR system

As shown in Fig.1, LPG is introduced into the intake

manifold. Proper mixing of LPG with intake charge was

achieved with the help of LPG nozzle. LPG nozzle speci-

fications are provided in Table 3. LPG fuel consumption is

616 P. Brijesh et al.

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described as equivalent of diesel fuel energy. LPG usage

rate is calculated using Eq. (1):

LPG% _mLPG LCVLPG

_mLPG LCVLPG _mdiesel LCVdiesel 100; 1

Fig. 1 Experimental test rig

Table 1 Specifications of measuring instruments and associatedmeasurement uncertainty

Measured

parameters

Instrument; make-model Uncertainty Relative

error

In-cylinder

pressure

Dynamic pressure

transducer; PCB

piezotronics-111A22

1 % 1 %

Fuel line

pressure

Engine speed Encoder; kubler-3700 5 rpm 0.34 %

Fuel mass

flow rate

DP transmitter;

Yokogawa-EJA110A

0.5 % 0.5 %

Air and EGR

mass flowrate

Pressure transmitter;

Wika-SL1

1 % 1 %

LPG mass

flow rate

Rotameter; Eureka

Industrial Equipments-

SSRS-MGS-4E

5 % 5 %

Engine load Load cell; Sensortronics-

60001

0.075 kg 0.625 %

Inlet and

exhaust gas

temperature

Thermocouple (k-type);

Radix-SS316

1 C 0.34 %

Table 2 Specifications of engine

Compression ratio range 18:112:1

Cylinder bore 9 stroke 87.5 mm 9 110 mm

Displacement 661 cc

Max. power 3.5 kW@ 1,500 rpm

Piston bowl shape Hemisphere

Piston bowl diameter 52 mm

Connecting rod length 234 mm

Inlet and exhaust valve diameter 34 mm

Inlet valve opens -364.5 CAD aTDC

Inlet valve closes -144.5 CAD aTDC

Exhaust valve opens 144.5 CAD aTDC

Exhaust valve closes 364.5 CAD aTDC

After treatment system Oxidizing catalytic converter

Reduction of emissions and fuel consumption 617

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where LCV is the lower calorific value of the fuel, _m

denotes the mass flow rate.

An EGR system, suitable for handling various types of

EGR such as UCEGR, OEGR, etc., has been implemented.

An exhaust plenum, as shown in Fig.1, is provided in theexhaust line to diminish the flow pulsations. The inlet

plenum is used to dampen intake line pulsations as well as

to homogeneously mix exhaust gases and fresh air. As

depicted in Fig. 1, a counter flow heat exchanger is used

for achieving UCEGR, capable of reducing the temperature

of the exhaust gas at the exit of the cooler to room tem-

perature. A drain plug is provided in the EGR cooler for

removing condensate from the recirculation line. EGR

temperature was measured at a location just before the inlet

plenum in the EGR line and maintained around 45 C

during the investigation. A two-way (oxidizing) catalytic

converter, as shown in Fig. 1, is used in the exhaust line forachieving OEGR. Tappings for EGR are provided in such a

way that recirculation of exhaust gases can be done from

the front and/or back of the catalytic converter. So, various

OEGR/EGR ratios can be achieved.

The EGR percentage is calculated and adjusted using the

Eq. (2):

EGR% _mairwithoutEGR _mairwithEGR

_mairwithoutEGR 100 2

Details of the test fuels

All experiments were conducted with unblended diesel fuel.

LPG fuel was used along with diesel fuel to achieve the RCCI

mode of combustion. The properties of diesel and LPG were

measured and tabulated in Tables 4 and5. A carbonhydro-

gennitrogensulphur (CHNS) elemental analyser was used

to measure the percentage of carbon, hydrogen, nitrogen and

sulphur in diesel fuel based on the principle of Dumas method

which involves the complete and instantaneous oxidation of

the sample by flash combustion. Thecombustion products are

separated by a chromatographic column and detected by the

thermal conductivity detector (TCD), which gives an output

signal proportional to the concentration of the individual

components of the mixture. Composition and physical prop-

erties of LPG were measured using a gas chromatograph with

high resolution mass spectrometer (GC-HRMS).

Measurement of exhaust gas emissions

Two different tap locations, as shown in Fig. 1, have been

provided in the exhaust line to take exhaust gas samples.

A Kane exhaust gas analyzer was used to measure exhaust

emissions such as NO, NO2, HC, CO, CO2, etc., while the

particulate matter emission was measured using Minivol

tactical air sampler (TAS). Detailed information of

instruments is provided in Table6. Undiluted exhaust gassamples were used for evaluation of exhaust gas emissions.

All the runs were conducted with catalytic converter, as

shown in Fig. 1, in the exhaust line, so emission analysis

was performed for tail-pipe exhaust gases.

Testing methodology

As discussed in our previous work (Brijesh et al. 2013),

significant reduction in NOx and PM has been achieved

Table 4 Diesel fuel properties Measured property Value

Specific gravity @

15 C

0.823

Lower calorific value,

MJ/kg

41.23

Viscosity @ 40 C,

mm2/s

3.6

Autoignition

temperature, C

210

Carbon, wt% 82.68

Hydrogen, wt% 13.83

Nitrogen, wt% 3.49

Sulphur, wt% 0

Table 5 LPG fuel properties Measured property Value

Density @ 25 C,

kg/m31.98

Lower calorific

value, MJ/kg

46.48

Autoignition

temperature, C

452

Ethane, vol% 10.38

Propene, vol% 46.50

Butene, vol% 21.27

i-Butane, vol% 3.39

n-Butane, vol% 17.31

i-Pentane, vol% 0.24

n-Pentane, vol% 0.91

Table 3 Specifications of diesel and LPG fuel injection system

Specification Diesel injection

system

LPG injection

system

Fuel injection pressure

(absolute)

220 bar 1 bar

Number of nozzle holes 3 24

Nozzle hole diameter 0.288 mm 2 mm


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with moderate rate of UCEGR. Attempts are made here to

achieve further reduction in emissions with various meth-

ods as discussed below.

Oxidized EGR (OEGR)

In this work, various runs have been carried out to inves-

tigate the effects of OEGR. The percentage of OEGR wasvaried from 0 to 100 % OEGR from run 1 to 3, with run 2

being executed with 50 % OEGR. All the runs have been

carried out at an optimized set of input parameters i.e. -15

CAD aTDC injection timing, 18 CR, 220 bar injection

pressure and 25 % UCEGR for this engine obtained

through our previous work (Brijesh et al. 2013). Run 1 was

conducted both with and without the catalytic converter in

the exhaust line to study the effect of catalytic converter on

emissions.

Reactivity controlled compression ignition (RCCI)

In this work, RCCI has been achieved using fuels with

varying reactivities. LPG fuel with low reactivity was

inducted along with air, while diesel fuel with high reac-

tivity was injected in the cylinder. Effect of combinations

of these fuels on performance and emissions of the engine

has been studied. Table7 gives the list of experimental

runs carried out to achieve optimized RCCI. All runs, as

mentioned in Table7, were carried out by varying the LPG

percentage from 0 to 40 % with a step size of 10 %. Run 1

was carried out at an optimized set of input parameters i.e.

-15 CAD aTDC injection timing, 18 CR, 220 bar injection

pressure and 25 % UCEGR for this engine obtainedthrough our previous work (Brijesh et al. 2013). The pre-

vious studies also showed encouraging results with retar-

ded injection timing (-10 CAD aTDC) and lower UCEGR

rate (*20 %) (Brijesh et al. 2013, 2014a). Hence, runs 2

and 3, as shown in Table 7, have also been carried out.

Effect of CR on RCCI has been investigated by changing

the CR from 18 to 16 (see run 4 in Table7).

All the tests of OEGR and RCCI were conducted at a

constant speed of 1,500 rpm. The engine is generally

operated at approximately 75 % load in practical applica-

tions. So, all the runs of OEGR and RCCI were carried out

for 75 % load condition (*6.5 bar IMEP). Uncertainty

associated with BTE was found to be 1.80 %. It was

computed using the approach of differential method of

propagating errors based on the Taylor theorem (Kline and

Mcclintock 1953), as discussed in our previous work(Brijesh et al. 2013).

Results and discussion

Effects of OEGR and LPG on engine performance and

emissions have been studied. A detailed analysis of various

outputs such as NOx, PM, HC, CO and BTE has been

executed.

Effect of OEGR on engine performance and emissions

Engine-out and tail-pipe exhaust gases were measured for

run 1 at 75 % load to study the effect of catalytic converter

on emissions and also to know the quantity of exhaust

species present in various OEGR/EGR ratios. The engine-

out values of NOx, PM, HC, CO and CO2for run 1 at 75 %

load are 2.31, 0.96, 0.30, 19.79 and 641 g/kWh, respec-

tively (values are not shown in Fig. 2). The tail-pipe values

of NOx, PM, HC and CO for the same run at 75 % load, as

given in Fig.2, are 2.26, 0.36, 0.26 and 8.63 g/kWh,

0

2

4

6

8

10

0/100 50/50 100/0

NOx,PM,HC,CO,g/kWh

OEGR/EGR, %

CO NOx PM HC

Fig. 2 Effect of OEGR on NOx, PM, HC and CO emissions

Table 6 Specifications of measuring instruments and associated

measurement uncertainty

Measured

parameters

Instrument; make-model Uncertainty

NO Flue gas analyzer; Kane-

KM9106

5 %

NO2 5 %

HC

5 %CO 5 %

Particulate matters MinivolTM

TAS; Airmetrics 5 %

Table 7 Run matrix to study the effects of LPG

Run no. SOI, CAD aTDC UCEGR, % CR

1 -15 25 18

2 -10 25 18

3 -15 20 18

4 -15 25 16


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respectively. The tail-pipe CO2 was increased with cata-

lytic converter in the exhaust line and found to be 667 g/kWh (this value is not shown in Fig. 2). It may be con-

cluded that catalytic converter in exhaust line plays a major

role in oxidization of HC, CO and PM, resulting a signif-

icant reduction in tail-pipe HC (*13 %), CO (*56 %)

and PM (*63 %) was achieved. Temperature of exhaust

gas 40 mm before the catalytic converter was measured

and found to be 225 C for the above-mentioned operating

condition. Amann (Amann 1980) had observed almost

similar conversion efficiency of CO (*57 %) and HC

(*20 %) for oxidizing catalytic converter at the temper-

ature of 235 C during his study with homogeneous charge

passenger car engine. As expected, CO2 was increased byapproximately 4 % as a result of oxidation of reacting

species. Effect of catalytic converter on NOxand BTE was

found to be insignificant.

Effect of various OEGR/EGR ratios on the NOx, PM,

HC and CO emissions is shown in Fig. 2. Results, as shown

in Fig.2, indicate that lower PM and NOx are achieved

with higher OEGR/EGR ratio. Higher concentrations of

CO2 and lower concentrations of reacting species with

increased OEGR lead to higher ignition delays. Higher

ignition delay increases premixed HRR, as a result, lower

PM was observed with increased OEGR. Higher premixed

HRR peaks with increasing ignition delays are, to a certain

extent, common with conventional combustion mode of CI

engines, but not always with advanced modes of combus-

tion. During this study, lower premixed HRR peaks, as

shown in Fig. 3, are observed with increased OEGR indi-

cating sluggish reaction rate during premixed combustion

with increased CO2. This reduces in-cylinder peak tem-

perature, and hence, reduction in NOx was also observed

with increased OEGR/EGR ratio. Figure2 also shows a

significant reduction in CO with increase in OEGR/EGR

ratio, but HC is increased. Two main reasons for reduction

of CO are identified: one is lower concentrations of CO in

the recirculation gases with increased OEGR/EGR ratio,

and the other is too slow oxidation at lean regions to form

significant CO. The later was supported by the observation

of Ekoto et al. (Ekoto et al. 2009). Results of their inves-

tigation showed that the fuel oxidation is too slow to form

considerable amount of CO at lower average cylindertemperature. This slow oxidation also supports the

increasing trend of HC along with decreasing CO with

increased OEGR/EGR ratio. Effect of OEGR on BTE was

found to be insignificant and, hence, is not shown in Fig. 2.

A considerable reduction in CO (*84 %), PM (*42 %)

and NOx (*23 %) has been achieved with OEGR com-

pared to EGR; however, HC was increased by nearly 98 %.

Effect of LPG on engine performance and emissions

Figure4 shows the effects of LPG on PM and NOxfor the

runs described in Table7. Reduction in PM was observedwith increased LPG percentage for each run. Similar trend

was observed by Taniguchi et al. (Taniguchi et al. 2012)

with a natural gas and diesel-fuelled engine. Effect of LPG,

as shown in Fig. 4a, is observed to be significant in runs 1

and 3 (*45 % reduction in PM) compared to runs 2 and 4

(*25 % reduction in PM), indicating that the combination

of LPG with early direct-injected diesel fuel and higher

CR, in the range of study, is effective in reducing PM.

Early injection allows better mixing and, hence, reduces

the formation of PM and higher average cylinder temper-

ature, as a result higher CR, enhances oxidation rate of PM.

The values of NOxagainst LPG percentages for all runs are

plotted in Fig.4b. Minor reduction in NOx emissions are

found for all runs with lower flow rates of LPG. However,

NOx was reduced considerably with higher LPG percent-

age (*43 % reduction with 40 % LPG). The reduction of

NOxand PM with increased LPG is elucidated using HRR

traces in Effect of LPG on combustion characteristics

section. The general trade-off between NOx and PM was

clearly visible in Fig. 4a and b, where runs 1 and 2 (18 CR

and 25 % UCEGR) were found to be the most favourable.

The effects of LPG on HC and CO emissions for various

runs are shown in Fig. 5. Figure5a shows the values of HC

of all runs for various LPG percentages. A fraction of LPG-

air mixture is typically trapped in crevices during the

compression stroke. As a result, higher concentrations of

HC were observed with higher amounts of LPG. Similar

results were observed by Poonia et al. (Poonia et al. 1999)

during their investigation with LPG and diesel-fuelled

engine. Their results showed that HC was reduced with

increasing quantity of pilot diesel fuel i.e. reducing the

quantity of primary LPG fuel. The values of tail-pipe CO

of all runs for various LPG percentages are given in

0

10

20

30

40

50

-10 0 10 20 30

HeatReleaseRate,J/degree

CAD a TDC

0/100 OEGR/EGR%

50/50 OEGR/EGR%

100/0 OEGR/EGR%

TDC

Fig. 3 Effect of OEGR on heat release rate


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Fig.5b. Figure5b shows that a significant reduction in CO

is achieved till approximately 20 and 10 % LPG for runs 2

and 4, respectively. In contrast, as shown in Fig. 5b, asmaller amount of reduction in CO is observed till 20 %

LPG with runs 1 and 3, beyond which CO is reduced

drastically with increasing LPG percentage (approximately

40 and 80 % reduction with 30 and 40 % LPG, respec-

tively). To understand the above results, engine-out CO

emissions were measured for all runs and increasing

amounts of CO were found with increased LPG percentage

for all runs (not shown here). Increasing engine-out CO and

decreasing tail-pipe CO with increased LPG percentage

indicate that the oxidization of CO in catalytic converter is

higher than the formation of CO in the cylinder as LPG

percentage increases. Temperature of exhaust gases 40 mmbefore and after the catalytic converter was measured for

all runs to elucidate the varied rates of reduction of tail-

pipe CO for different runs (Fig.5b), plotted in Fig.6.

Results show that exhaust gas temperature is found to be

higher after the catalytic converter than before, for higher

percentages of LPG in all runs. This was possible only with

secondary burning of large amounts of un-burnt hydro-

carbon in the catalytic converter. As a result, temperature

inside the catalytic converter reaches an effective

temperature (*250 C) and, hence, improves the oxidi-

zation rate of CO. Nearly 70 % CO was reduced in a

similar investigation carried out by Amann (Amann1980).Figure6a shows that temperature after the catalytic con-

verter becomes higher than before the catalytic converter

beyond 30 % LPG for runs 1 and 3. While similar trend is

observed in Fig. 6b for runs 2 and 4 beyond 20 and 10 %

LPG, respectively. It may be concluded that conversion

efficiency of CO reaches close to maximum at 20 and 10 %

LPG for runs 2 and 4, respectively, whereas at 30 % LPG

for runs 1 and 3. As a result, considerable reduction in CO

is achieved till approximately 20 and 10 % LPG for runs 2

and 4, respectively, while CO reduction continued even

beyond 30 % LPG for runs 1 and 3.

Figure7 shows the effect of LPG on BTE, where BTE isreduced with increased LPG percentage. The inducted

LPG-air mixture is trapped in crevices during the com-

pression stroke and increases crevice losses, which in turn

reduces BTE. However, BTE loss may be reduced using

lower percentages of LPG. Negative effect of lower CR on

BTE is clearly observed by comparing the results of runs 1

and 4. The effect of LPG on HC and BTE, as shown in

Figs.5a and7, is observed to be better for run 1 compared

to run 2. Figure8shows that the HRR traces of runs 2 and

0.10

0.16

0.22

0.28

0.34

0.40

0 10 20 30 40

PM,g/kWh

LPG, %

Run 1 Run 2

Run 3 Run 4

a

0

1

2

3

4

5

0 10 20 30 40

NOx,g/kWh

LPG, %

Run 1 Run 2

Run 3 Run 4

b

Fig. 4 Effect of LPG on a PM and b NOx emissions

0.00

0.32

0.64

0.96

1.28

1.60

0 10 20 30 40

HC,g/kWh

LPG, %

Run 1 Run 2

Run 3 Run 4

a

0.0

1.5

3.0

4.5

6.0

7.5

0 10 20 30 40

CO,g

/kWh

LPG, %

Run 1 Run 2

Run 3 Run 4

b

Fig. 5 Effect of LPG on a HC and b CO emissions


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3 are slightly shifted towards the compression stroke, while

for the run 4 it is shifted much towards the expansion

stroke compared to run 1. Thus, the combustion phasing of

run 1 seems to be the optimum for reducing NOx and PM

without altering BTE. Hence, run 1 was chosen to study the

effects of LPG on combustion parameters in details.

Results, as discussed above, indicate that reduction in

PM, NOx and CO is achieved with lower amount of LPG

(*10 %) without altering BTE and with acceptable change

in values of HC. Further increase in LPG percentage

resulted in reduction of PM, CO and NOx

, with consider-able penalty on BTE and HC.

Optimum LPG percentage was also found using multi

response signal-to-noise ratio (MRSN) analysis, as men-

tioned in our previous work (Brijesh et al. 2013). BTE,

NOx, PM, HC and CO were treated as response variables

for optimization. As discussed earlier, HC was increased

and BTE was decreased significantly with increasing LPG

percentage. Hence, higher importance was given to HC and

BTE compared to CO, PM and NOx. Based on the relative

importance of each output variable, weighting factors (wi)

of 0.3, 0.3, 0.15, 0.15 and 0.1 were assigned for BTE, HC,

PM, CO and NOx, respectively. All weighting factors addup to unity. Higher values of MRSN represent more

desirable outcomes. Results, as tabulated in Table8, indi-

cate that the MRSN ratio of run 1 with 10 % LPG (0.976)

is the maximum. Hence, RCCI achieved with lower per-

centage of LPG (*10 %) is more beneficial for overall

reduction in emissions without altering BTE. For under-

standing the results better, a detailed study of heat release

and pressure traces has been carried out.

Effect of LPG on combustion characteristics

The HRR traces, as shown in Fig. 9, corresponding to run 1with various LPG percentages have been studied. Figure9

indicates that HRR traces of run 1 with increasing per-

centages of LPG are shifted towards the expansion stroke.

A reduction in the values of premixed HRR peak and minor

increase in ignition delays are also observed with increased

LPG percentages. It indicates that the presence of LPG

slows down the chemical reaction rate during premixed

combustion. The reaction rates of LPG and diesel fuel have

been calculated using single-step global mechanism

175

200

225

250

275

300

0 10 20 30 40

T

emperature,C

LPG, %

Run1-before cat-con Run1-after cat-con


a

200

235

270

305

340

375

0 10 20 30 40

Temperature,C

LPG, %



b

Fig. 6 Temperature of exhaust gas before and after the catalytic converter for a runs 1 and 3, andb runs 2 and 4 with varying LPG percentages

24

25

26

27

28

29

0 10 20 30 40

BTE

,%

LPG, %

Run 1 Run 2

Run 3 Run 4

Fig. 7 Effect of LPG on brake thermal efficiency

-5

5

15

25

35

45

55

-30 -20 -10 0 10 20 30 40 50 60


CAD aTDC

Run 1 Run 2

Run 3 Run 4

TDC

Fig. 8 HRR curves for various runs at 10 % LPG


1 3


9/11

suggested by Westbrook and Dryer (Westbrook and Dryer

1981) to confirm the observation, and were found to be

5.53 9 108 and 7.91 9 108 gmol/cm3 s, respectively, at

an equivalence ratio of one. The values indicate that LPG

fuel is having lower reaction rate compared to diesel fuel,

and hence, LPG slows down the combustion phenomena

during the premixed stage. This leads to a lower in-cyl-

inder peak temperature and, hence, lower NOx emissionswere observed with higher percentages of LPG. Premixed

to diffusion combustion ratios of run 1 with 0, 10, 20, 30

and 40 % LPG, calculated with the help of cumulative heat

analysis data, were found to be 0.85, 0.97, 1.00, 1.02 and

1.08, respectively. A minor increase in ratio of premixed to

diffusion combustion indicates that premixed part of

combustion is increased with increasing LPG percentage

and, hence, produces lower PM. As a result, as shown in

Fig.4, improvement in NOx-PM trade-off has beenTable8

MRSNanalysisofRun1

withvaryingLPGpercentage

Run1with

LPG%

Lossfunction,

Lij

Normalized

lossfunction,

Sij

LijLavg

Weigh

tednormalized

lossfu

nction,wi

Sij

T

otalloss

function,

P

wiSij

MRSNratio

BTE

NO

x

PM

HC

CO

BTE

NO

x

PM

HC

CO

BTE

NO

x

PM

HC

CO

0

0.0

012

9.7

95

0.1

10

0.0

21

41.4

81

0.9

41

1.622

1.9

15

0.0

32

1.7

84

0.2

82

0.1

62

0.2

87

0.0

10

0.2

68

1

.009

-0.0

39

10

0.0

012

6.9

63

0.0

51

0.0

72

36.9

50

0.9

30

1.153

0.8

94

0.1

07

1.5

89

0.2

79

0.1

15

0.1

34

0.0

32

0.2

38

0

.799

0.9

76

20

0.0

013

5.6

64

0.0

44

0.3

87

25.0

20

0.9

68

0.938

0.7

69

0.5

76

1.0

76

0.2

90

0.0

94

0.1

15

0.1

73

0.1

61

0

.834

0.7

90

30

0.0

014

4.6

26

0.0

44

1.0

13

11.5

82

1.0

56

0.766

0.7

60

1.5

08

0.4

98

0.3

17

0.0

77

0.1

14

0.4

52

0.0

75

1

.034

-0.1

47

40

0.0

015

3.1

43

0.0

38

1.8

65

1.2

55

1.1

05

0.521

0.6

63

2.7

77

0.0

54

0.3

32

0.0

52

0.0

99

0.8

33

0.0

08

1

.324

-1.2

19

Boldvaluessignifyhighlightthebestoperatingrun

-5

5

15

25

35

45

55

-30 -20 -10 0 10 20 30 40 50 60


CAD aTDC

Run1_0%LPG

Run1_10%LPG

Run1_20%LPG

Run1_30%LPG

Run1_40%LPG

TDC

Fig. 9 Heat release rate traces for run 1 with varying LPG percentage

0

10

20

30

40

50

60

70

-30 -20 -10 0 10 20 30 40 50 60

CylinderPressure,bar

CAD aTDC

Run1_0%LPGRun1_10%LPG

Run1_20% LPG

Run1_30%LPG

Run1_40%LPG

TDC

Fig. 10 Pressure traces for run 1 with varying LPG percentage


1 3


10/11

observed for run 1 with increasing LPG percentage com-

pared to optimized LTC i.e. run 1 without LPG.

Variations of in-cylinder pressure, as a function of crank

angle, for run 1 with various LPG percentages are plotted

in Fig.10. The in-cylinder pressure curves are altered

extensively during various runs. In-cylinder pressure traces

of run 1 with LPG were shifted towards the expansion

stroke, thus indicating a shifting of the combustion phase

because of lower reactivity LPG fuel. As discussed earlier,

LPG slows down the reaction rate, and hence, lower peak

pressures were found with increasing amount of LPG. As aresult, reduction in BTE was observed with increased LPG

percentage.

Result evaluation

The values of NOx, PM, HC, CO and BTE for the opti-

mized LTC (-15 CAD aTDC injection timing, 18 CR,

220 bar injection pressure, 25 % UCEGR and 0 % LPG)

and for the optimized RCCI (-15 CAD aTDC injection

timing, 18 CR, 220 bar injection pressure, 25 % UCEGR

and 10 % LPG) runs at 75 % load are compared in Table 9

based on results of Figs. 4,5and7. Table9indicates that aconsiderable reduction in PM (*30 %), NOx (*16 %)

and CO (*6 %) with an acceptable change in value of HC

is achieved with the optimized RCCI run compared to that

for optimized LTC run. An insignificant change in BTE

was observed with the optimized RCCI run.

OEGR and LPG both offer a considerable reduction in

PM, NOxand CO levels with an acceptable change in HC.

OEGR offers better reduction in emissions with simple and

economical modifications in an existing engine compared

to LPG; emerging as an effective method. However,

combination of OEGR and LPG might be useful to achieve

ultra-low emissions level in CI engines.

Conclusions

In this work, effect of OEGR and LPG on engine perfor-

mance, emissions and combustion parameters has been

studied at 75 % load condition. An oxidizing catalytic

converter is used in the exhaust line for achieving OEGR.

Study showed that considerable reduction in NOx and PM

through improved LTC was achieved with increased

OEGR. Higher concentrations of CO2 and lower concen-

trations of reacting species with higher percentage of

OEGR increased the ignition delay and reduced the pre-

mixed HRR peak. Results also demonstrated the impor-

tance of catalytic converter in reduction of tail-pipe PM,

CO and HC.

RCCI has been achieved using commercially available

LPG with the percentage being varied from 0 to 40 %.

Reduction in PM, NOx and CO emissions was observed

with increased LPG percentage, but has an adverse effecton HC and BTE. Improvement in NOx-PM trade-off was

observed with increasing amount of LPG. Result showed

that RCCI achieved with lower amount of LPG (*10 %)

was found to be the optimum for reducing PM, NOx and

CO with the acceptable changes in the values of HC and

BTE.

Combination of OEGR and LPG will be considered as a

scope of future work to achieve ultra-low emissions level

in CI engines. The effect of OEGR and LPG on engine

performance and emissions will also be investigated at

various engine load condition i.e. 10, 25, 50 and 100 % in

near future.

Acknowledgments The authors gratefully acknowledge the Indus-

trial Research and Consultancy Centre (IRCC), IIT Bombay and

Department of Science and Technology (DST), India for funding

towards the VCR engine for research work. The authors are also

thankful to the Sophisticated Analytical Instrument Facility (SAIF),

IIT Bombay for permitting to find the properties of LPG and diesel

fuel.

References

Amann CA (1980) Control of the homogeneouscharge passenger

car enginedefining the problem. SAE-801440Asad U, Zheng M (2008) EGR oxidation and catalytic fuel reforming

for diesel engines. ASME ICE; ICES20081684

Asad U, Zheng M, Han X, Reader GT, Wang M (2008) Fuel injection

strategies to improve emissions and efficiency of high compres-

sion ratio diesel engines. SAE 2008-01-2472

Bauner D, Laestadius S, Iida N (2009) Evolving technological

systems for diesel engine emission control: balancing GHG and

local emissions. Clean Techn Environ Policy 11:339365

Brijesh P, Sreedhara S (2013) Exhaust emissions and its control

methods in compression ignition engines: a review. Int J

Automot Technol 14:195206

Table 9 Comparison of various parameters

Operating run

(Inj. timing, CR, EGR, LPG)

BTE,

%

CO,

g/kWh

HC,

g/kWh

NOx,

g/kWh

PM,

g/kWh

Optimized LTC (-15, 18, 25, 0) 28.41 6.44 0.15 3.13 0.33

Optimized RCCI (-15, 18, 25, 10) 28.58 6.07 0.42 2.63 0.23

% Change (RCCI compared to LTC) 0.60 (:) -5.75 (;) 180.00 (:) -15.97 (;) -30.30 (;)


1 3


11/11

Brijesh P, Chowdhury A, Sreedhara S (2013) Effect of ultra-cooled

EGR and retarded injection timing on low temperature combus-

tion in CI engines. SAE 2013-01-0321

Brijesh P, Chowdhury A, Sreedhara S (2014a) Simultaneous reduc-

tion of NOx and soot using ultra-cooled EGR and retarded

injection timing in a diesel engine. Int J Green Energy. doi:10.

1080/15435075.2013.841164

Brijesh P, Harshvardhan A, Sreedhara S (2014b) A study of

combustion and emissions characteristics of a compression

ignition engine processes using a numerical tool. Int J Adv Eng

Sci Appl Math 6:1730

Dec JE (2009) Advanced compression ignition enginesunderstand-

ing the in-cylinder processes. Proc Combust Inst 32:27272742

Dec JE, Sjoberg M, Hwang W (2009) Isolating the effects of EGR on

HCCI heat-release rates and NOxemissions. SAE 2009-01-2665

Dempsey AB, Reitz RD (2011) Computational optimization of

reactivity controlled compression ignition in a heavy-duty

engine with ultra low compression ratio. SAE 2011-24-0015

Ekoto IW, Colban WF, Miles PC, Park SW, Foster DE, Reitz RD,

Aronsson U, Andersson O (2009) UHC and CO emissions

sources from a light duty diesel engine undergoing dilution

controlled low temperature combustion. SAE 2009-24-0043

Fernandez JR, Tsolakis A, Cracknell RF, Clark RH (2009) Combining

GTL fuel, reformed EGR and HC-SCR after treatment system to

reduce diesel NOx emission-A statistical approach. Int J

Hydrogen Energy 34:27892799

Heywood JB (1988) Internal combustion engine fundamentals.

McGraw-Hill, New York

Hill SC, Smoot LD (2000) Modeling of nitrogen oxides formation and

destruction in combustion systems. Prog Energy Combust Sci

26:417458

Ilyas SZ, Khattak AI, Nasir SM, Qurashi T, Durrani R (2010) Air

pollution assessment in urban areas and its impact on human

health in the city of Quetta, Pakistan. Clean Technol Environ

Policy 12:291299

Kline SJ, Mcclintock FA (1953) Describing the uncertainties in single

sample experiments. Mech Eng 75:38

Kokjohn SL, Hanson RM, Splitter DA, Reitz RD (2009) Experiments

and modeling of dual-fuel HCCI and PCCI combustion using in-

cylinder fuel blending. SAE 2009-01-2647

Kook S, Bae C, Miles P, Choi D, Pickett LM (2005) The influence of

charge dilution and injection timing on low temperature diesel

combustion and emissions. SAE 2005-01-3837

Lata DB, Misra A, Medhekar S (2011) Investigations on the

combustion parameters of a dual fuel diesel engine with

hydrogen and LPG as secondary fuels. Int J Hydrogen Energy

36:1380813819

Maiboom A, Tauzia X, Hetet JF (2008) Influence of high rates of

supplemental cooled EGR on NOx and PM emissions of an

automotive HSDI diesel engine using an LP EGR loop. Int J

Energy Res 32:13831398

Nazar J, Ramesh A, Nagalingam B (2006) Studies on dual fuel

operation of Karanja oil and its bio-diesel with LPG as the

inducted fuel. SAE 2006-01-0237

Nieman DE, Dempsey AD, Reitz RD (2012) Heavy-duty RCCI

operation using natural gas and diesel. SAE 2012-01-0379

Pickett LM, Siebers DL (2004) Soot in diesel fuel jets: effects of

ambient temperature, ambient density, and injection pressure.

Combust Flame 138:114135

Pohlkamp K, Reitz R (2012) Reactivity controlled compression

ignition (RCCI) in a single-cylinder air-cooled HSDI diesel

engine. SAE 2012-32-0074

Poonia MP, Ramesh A, Gaur RR (1999) Experimental investigation

of the factors affecting the performance of a LPGdiesel dual

fuel engine. SAE 1999-01-1123

Splitter D, Wissink M, Kokjohn S, Reitz R (2012) Effect of

compression ratio and piston geometry on RCCI load limits

and efficiency. SAE 2012-01-0383

Taniguchi S, Masubuchi M, Kitano K, Mogi K (2012) Feasibility

study of exhaust emissions in a natural gas diesel dual fuel

(DDF) engine. SAE 2012-01-1649

Thompson T, Kimura Y, Durrenberger C, Webb A, Matias AIT,

Fraser M, Allen DT (2009) Estimates of the air quality benefits

of using natural gas in industrial and transportation applications

in Lima, Peru. Clean Technol Environ Policy 11:409423

Westbrook CK, Dryer FL (1981) Simplified reaction mechanisms for

the oxidation of hydrocarbon fuels in flames. Combust Sci

Technol 27:3143

Zheng M, Irick DK, Hodgson J (2002) Stabilizing excessive EGR

with an oxidation catalyst on a modern diesel engine. ASME ICE

38: 2002-ICE-455

Zheng M, Reader GT, Hawley JG (2004) Diesel engine exhaust gas

recirculationa review on advanced and novel concepts. Energy

Convers Manag 45:883900

Zheng M, Asad U, Kumar R, Reader GT, Mulenga MC, Bombardier

W, Wang M, Tjong J (2007) An investigation of EGR treatment

on the emissions and operating characteristics of modern diesel

engines. SAE 2007-01-1083


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Advanced combustion methods for simultaneous reduction of emissions and fuel consumption of compression ignition engines