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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
15
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
16
Bharat State emission standards
Results of Previous Study
Engine Specifications
17
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
18
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
19