Reactivity Controlled Compression Ignition for Simultaneous Reduction of Emissions and Fuel Consumption in Diesel Engines

Brijesh P., Chowdhury A., Sreedhara S.IC Engines and Combustion Laboratory

Indian Institute of Technology Bombay, India

2

Diesel engines are more popular over gasoline engines because of their higher

efficiencies

Simultaneous reduction of NOx and PM becomes a major challenge

Significant reduction in NOx and PM was achieved with

low temperature combustion (LTC) during our previous work*

However, PM and CO for optimized LTC run are still higher than the limit

suggested in standards

In this work, experimental study has been carried out to achieve Reactivity

Controlled Compression Ignition (RCCI) with liquefied petroleum gas (LPG)

LPG fuel with low reactivity was introduced into the intake manifold while diesel

with high reactivity was injected into the cylinder

Effects of LPG on engine performance and emissions have also been studied

Introduction

Brijesh P., Chowdhury A., and Sreedhara S. “Effect of Ultra-Cooled EGR and Retarded Injection Timing on Low Temperature Combustion in CI Engines.” SAE Technical Paper 2013-01-0321, 2013, doi:10.4271/2013-01-0321.

Experimental Test Rig

LPG was introduced into the intake manifold through LPG nozzle (24 holes, 2 mm dia. of each hole)

3

Testing Procedure

4

All runs, as shown in table, were carried out by varying LPG percentage from 0 to

40% with a step size of 10

LPG fuel consumption was described as an equivalent of diesel fuel energy

LPG usage rate was calculated by using the Equation,

Run 1 was carried out at an optimized set of input parameters for this engine

obtained through our previous work

Run no. SOI, CAD aTDC EGR, % CR

1 15 25 18

2 10 25 18

3 15 20 18

4 15 25 16

(%) 100LPG LPG

LPG LPG diesel diesel

m LCVLPG

m LCV m LCV

Testing Procedure (Contd.)

5

Composition and physical properties of LPG was measured by using Gas Chromatograph

with High Resolution Mass Spectrometer (GC-HRMS)

CHNS elemental analyser was used to measure percentage of carbon, hydrogen,

nitrogen and sulphur in diesel

Reaction rates of LPG and diesel were calculated by using single step global mechanism

of Westbrook and Dryer and found to be 5.53×108 and 7.91×108 gmol/cm3.s respectively

Measured property of LPG Value

Density @ NTP, kg/m3 1.98

Lower calorific value, MJ/kg 46.48

Auto ignition temperature, oC 460

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

Measured property of diesel Value

Specific gravity @ 15oC 0.823

Lower calorific value, MJ/kg 41.23

Viscosity @ 40oC, mm2/s 3.6

Auto ignition temperature , oC 210

Carbon, wt% 82.68

Hydrogen, wt% 13.83

Nitrogen, wt% 3.49

Sulphur, wt% 0

Effect of LPG on PM and NOx

6

Reduction in PM was observed with increased LPG percentage

Effect of LPG was observed significant in runs 1 and 3 compared to other runs

Minor changes in NOx were found for all runs with lower flow rates of LPG

However, NOx was reduced considerably with higher LPG percentage

Runs 1 and 2 were found most favourable for improved NOx-PM trade-off

1

2

3

4

5

6

0 10 20 30 40

NO

x, g

/kW

.hr

LPG, %

Run 1 Run 2Run 3 Run 4

b

0.10

0.16

0.22

0.28

0.34

0.40

0 10 20 30 40

PM

, g/k

W.h

r

LPG, %

Run 1 Run 2Run 3 Run 4

aRun no. SOI, CAD aTDC EGR, % CR

1 15 25 18

2 10 25 18

3 15 20 18

4 15 25 16

Effect of LPG on CO and HC

7

CO was reduced significantly with the introduction of LPG fuel

Considerable reduction in CO was achieved till LPG is around 10%

Further reduction in CO was not observed with increasing percentage of LPG

A fraction of LPG-air mixture might have been trapped in crevices during the

compression stroke

As a result, higher HC was observed with higher amount of LPG

0.1

0.2

0.3

0.4

0.5

0.6

0 10 20 30 40

CO

, g/k

W.h

r

LPG, %

Run 1 Run 2Run 3 Run 4

a

0.00

0.32

0.64

0.96

1.28

1.60

0 10 20 30 40

HC

, g/k

W.h

r

LPG, %

Run 1 Run 2Run 3 Run 4

bRun no. SOI, CAD aTDC EGR, % CR

1 15 25 18

2 10 25 18

3 15 20 18

4 15 25 16

Effect of LPG on BTE

8

BTE was reduced with increased LPG percentage

Inducted LPG-air mixture traps in crevices during the compression stroke which in

turn reduces BTE

Effect of LPG on HC and BTE was observed to be better for run 1. Hence, run 1 is

found optimal

RCCI achieved with low LPG (10%) seems to be optimum for reduction of PM and

CO with the acceptable values of HC, NOx and BTE

24

25

26

27

28

29

0 10 20 30 40

BT

E, %

LPG, %

Run 1 Run 2Run 3 Run 4

Run no. SOI, CAD aTDC EGR, % CR

1 15 25 18

2 10 25 18

3 15 20 18

4 15 25 16

The combustion phasing of run 1 seems to be optimum for

reduction of NOx and PM without altering BTE

The HRR traces of runs 2 and 3 are slightly shifted towards the compression stroke

while run 4 is shifted much towards the expansion stroke as compared with run 1

Run 1 was chosen to study the effects of LPG on combustion parameters9

5

15

25

35

45

55

65

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

Cyl

inde

r P

ress

ure,

bar

CAD aTDC

Run 1 Run 2

Run 3 Run 4

TDC

-5

5

15

25

35

45

55

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

Net

Hea

t Rel

ease

, J/d

egre

e

CAD aTDC

Run 1 Run 2

Run 3 Run 4

TDC

Effect of LPG on Combustion Parameters

Run no. SOI, CAD aTDC EGR, % CR

1 15 25 18

2 10 25 18

3 15 20 18

4 15 25 16

A reduction in premixed HRR peak and minor increase in ignition delays are

observed with increased LPG

The presence of LPG slow down the chemical reaction rate during premixed

combustion

Minor changes in ratio of premixed to diffusion combustion were observed with

increased rate of LPG

As a result, wider and flatter HRR traces, improved LTC, were observed

Effect of LPG on Combustion Parameters (Contd.)

10

-5

5

15

25

35

45

55

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

Net

Hea

t Rel

ease

, J/d

egre

e

CAD aTDC

Run1_0%LPG Run1_10%LPGRun1_20%LPG Run1_30%LPGRun1_40%LPG Base run

TDC

Run 1

SOI -15

EGR 25%

CR 18

Similar to the HRR traces, in-cylinder pressure traces of run 1 with LPG were also

shifted towards the expansion

The combustion phases were shifted because of increasing lower reactivity LPG fuel

Lower peak pressures were found with increasing LPG percentage, hence, reduction

in BTE was observed 11

0

10

20

30

40

50

60

70

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

Cyl

inde

r P

ress

ure,

bar

CAD aTDC

Run1_0%LPG Run1_10%LPGRun1_20% LPG Run1_30%LPGRun1_40%LPG Base run

TDC

Effect of LPG on Combustion Parameters (Contd.)

Run 1

SOI -15

EGR 25%

CR 18

Reduction of Emissions with RCCI

12

RCCI with lower amount of LPG (10%) offers significant reduction in PM and CO with

the acceptable values of HC, BTE and NOx

Operating run(Inj. timing, CR, EGR, LPG)

BTE,%

CO,g/kW.hr

HC,g/kW.hr

NOx,g/kW.hr

PM,g/kW.hr

Base run (27, 18, 0 , 0) 26.61 0.68 0.30 19.43 0.58 

Optimized LTC (15, 18, 25, 0) 28.41 0.52 0.15 2.28 0.33

Optimized RCCI (15, 18, 25, 10) 28.58 0.26 0.42 2.51 0.23

% Change (RCCI compared to base)

7.40 () 61.76 () 40.00 () 87.10 () 60.34 ()

% Change (RCCI compared to LTC)

0.60 () 50.00 () 180.00 () 10.10 () 30.30 ()

Conclusions

Reactivity controlled compression ignition (RCCI) achieved with low

LPG (10%) found to be optimum for further reduction of PM and CO

with the acceptable change in values of HC, NOx and BTE

Reduction in premixed HRR peak and minor increase in ignition delays

were observed with increasing percentages of LPG

Improved LTC, flatter and wider HRR traces, were achieved with

optimized RCCI

Reduction in PM, CO and NOx emissions were observed with increased

LPG percentage

HC was increased and BTE was decreased with increasing amount of

LPG

13

Thank You

14

Back Up

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LTC, simultaneous reduction in NOx and PM, was achieved with the optimum operating

parameters

Very low values of NOx and HC are achieved for the optimized run and are falling below

the limits stated in standards

PM and CO for optimized run are still higher than the limit suggested in standards

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Bharat State emission standards

Results of Previous Study

Engine Specifications

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Engine type Four-stroke, water cooled, direct injection VCR engine

Make Kirloskar Oil Engines Ltd.

Number of cylinders 1

Compression ratio 18:1 to 12:1

Cylinder bore stroke 87.5 mm 110 mm

Piston bowl shape Hemisphere

Piston bowl diameter 52 mm

Maximum power 3.5 kW @ 1500 rpm

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

Connecting rod length 234 mm

Fuel injection pressure range 180 to 250 bar

Fuel injection timing variation 27 to 7 CAD aTDC

Number of nozzle holes 3

Nozzle hole diameter 0.288 mm

Nozzle hole L/D ratio 2.78

Specifications of Measuring Devices

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Measured parametersInstrument; Make-Model

Operating range

Uncertainty /Accuracy

Relative error

In-cylinder pressure Dynamic pressure transducer; PCB piezotronics-111A22

0 345.5 bar ± 1% ± 1%Fuel line pressure

Engine speed Encoder; Kubler-3700 0 6000 rpm ± 5 rpm ± 0.34 %

Fuel mass flow rateDP Transmitter; Yokogawa-EJA110A

0 3.5 kg/hr ± 0.5 % ± 0.5 %

Air and EGR mass flow rate

Pressure transmitter; Wika-SL1

0 50 kg/hr ± 1% ± 1%

Engine loadLoad cell; Sensortronics-60001

0 50 kg ± 0.075 kg ± 0.625 %

Intake and exhaust gas temperature

Thermocouple (k type); Radix-SS316

0 1200°C ± 1°C ± 0.34 %

NO

Flue gas analyzer; Kane-KM9106

0 5000 ppm ± 5% ± 5%

NO2 0 1000 ppm ± 5% ± 5%

HC 0 2000 ppm ± 5% ± 5%

CO 0 100000 ppm ± 5% ± 5%

Particulate matters MinivolTM TAS; Airmetrics ± 5% ± 5%

Heat release analysis The first law of Thermodynamics is applied to control volume,

Where, Qhr is the heat released by combustion and Qht is the heat transfer with the chamber walls

dU and W can be calculated by using following equations:

Substituting equation (2) into equation (1) with an incremental angle basis:

.............................................................(1)hr htQ dU W Q

1

and ................................................................(2)

v

v

dU mc dT

mdT pdV Vdp pV mRTRc

dU pdV Vdp W pdVR

1

1 1

1Net heat release,

1 1

hr ht v

hr ht

net

dQ dQ c dV dp dVp V p

d d R d d d

dQ dQ dV dpp V

d d d d

dQ dV dpp V

d d d

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