Results and Discussion: Neat Palm Biodiesel Run Engine
5.4 Emission Analysis
advancement causes increase in ID for POME and vice versa (Figure 5.9). For the CR studied, the average IDs obtained for IT of 20ºBTDC are 15.33, 14.67, 14.33 and 13.17, whereas at 28ºBTDC, these value are 18.33, 17.67, 16.83 and 16.33. The IT advancement causes an average rise of ID by about 2% and 6% whereas retardation results an average drop of ID by about 12%.
At retarded IT, POME spray takes place at a crank angle closest to the TDC. At that instant, the atmosphere in the cylinder is more pressurized and heated comparable to other ITs. This makes the burn prone POME to ignite faster, locally as well as globally inside the cylinder.
Therefore, the retardation has more effect than advancement. Figure 5.10 show that advancing the IT provide a rise in the peak NHRR points. It is also clear that the curves are shifted towards the compression stroke as the IT advances. Though at an advance IT, the fuel burns for a longer duration and releases more heat, but it does not seem to increase BTHE as obtained at retardation as discussed in Section 5.2.3. This is due to the higher BSFC at advancement as opposed to retardation. The fact is also ascertained from the findings of Devan and Mahalakshmi (2009). The combustion analysis, therefore, reveals the setting of CR=18 and IT=20ºBTDC to be the optimum among all the combinations.
and 4.39%. At low to mid load regions, the CO2 emissions generated by POME are far lower than diesel emissions. However, at higher loads, high combustion temperatures cause additional oxidization of carbons to produce higher CO2 emissions. POME produces overall 17% lower CO2 emission than that of diesel.
(a) (b)
(c) (d)
Figure 5.9 Variation of ID with engine load for different CR and IT for neat POME run engine
(a) (b)
(c) (d)
Figure 5.10 Variation of NHRR with crank angle at 100% load for different CR and IT for neat POME run engine
10 12 14 16 18 20 22
0 20 40 60 80 100 120
Ignition Delay (deg.CA)
Engine Load (%) DIESEL(CR:17.5)
CR(POME):16 CR(POME):17 CR(POME):17.5 CR(POME):18
SPEED:1500 RPM IT(DIESEL):23ºBTDC
IT(POME):20ºBTDC
10 12 14 16 18 20 22
0 20 40 60 80 100 120
Ignition Delay (deg. CA)
Engine Load (%)
SPEED:1500 RPM IT(DIESEL):23ºBTDC
IT(POME):23ºBTDC
10 12 14 16 18 20 22
0 20 40 60 80 100 120
Ignition Delay (deg. CA)
Engine Load (%)
SPEED:1500 RPM IT(DIESEL):23ºBTDC
IT(POME):25ºBTDC
10 12 14 16 18 20 22
0 20 40 60 80 100 120
Ignition Delay (deg. CA)
Engine Load (%)
SPEED:1500 RPM IT(DIESEL):23ºBTDC
IT(POME):28ºBTDC
-10 10 30 50 70 90 110
330 340 350 360 370 380
Net Heat Release Rate (J/deg. CA)
Crank Angle (deg.CA)
DIESEL(CR:17.5) CR(POME):16 CR(POME):17 CR(POME):17.5 CR(POME):18 LOAD:100%
SPEED:1500 RPM IT(DIESEL):23ºBTDC
IT(POME):20ºBTDC
-10 10 30 50 70 90 110
330 340 350 360 370 380
Net Heat Release Rate (J/deg. CA)
Crank Angle (deg.CA) LOAD:100%
SPEED:1500 RPM IT(DIESEL):23ºBTDC
IT(POME):23ºBTDC
-10 10 30 50 70 90 110
330 340 350 360 370 380
Net Heat Release Rate (J/deg. CA)
Crank Angle (deg.CA) LOAD:100%
SPEED:1500 RPM IT(DIESEL):23ºBTDC
IT(POME):25ºBTDC
-10 10 30 50 70 90 110
330 340 350 360 370 380
Net Heat Release Rate (J/deg. CA)
Crank Angle (deg.CA) LOAD:100%
SPEED:1500 RPM IT(DIESEL):23ºBTDC
IT(POME):28ºBTDC
(a) (b)
(c) (d)
Figure 5.11 Variation of CO with engine load for different CR and IT for neat POME run engine
Figure 5.13 describe the variations of NOX emissions with respect to load. From no-load to full-load conditions, the average NOX emissions obtained for POME are 24, 32, 44, 59, 79 and 97 ppm, as opposed to 24, 40, 49, 61, 76 and 92 ppm for the diesel engine. This increasing tendency of NOX emission with respect to load is dependent on combustion temperature that is supported by EGT curves (Figure 5.4). At high load region, the increases in temperature speed up the thermal NOX formation (Heywood, 1988). That is the reason behind the higher NOX emission for POME at higher load region. However, NOX emission for POME is 4% higher than diesel emission in average. Figure 5.14 show that, at lower and higher load regions, HC emissions change with descending and ascending orders. For the POME run engine, the average HC emissions at no-load to full-load regions are 18, 14, 10, 8, 13, 18 ppm, whereas, for the diesel engine, the corresponding values are 30, 22, 17, 14, 15 and 19 ppm. At lower load regions, the combustion temperatures accomplish to a reasonably lower value to enable complete combustion. However, at higher load regions, the quantity of fuel supply increases to produce additional power to take up high load. These facts together are responsible for unburnt HC release (Aziz et al., 2006).
0 25 50 75 100 125
0 20 40 60 80 100 120
Carbon Monoxide (ppm)
Engine Load (%) DIESEL(CR:17.5) CR(POME):16 CR(POME):17 CR(POME):17.5 CR(POME):18
SPEED:1500 RPM IT(DIESEL):23ºBTDC
IT(POME):20ºBTDC
0 25 50 75 100 125
0 20 40 60 80 100 120
Carbon Monoxide (ppm)
Engine Load (%) SPEED:1500 RPM IT(DIESEL):23ºBTDC
IT(POME):23ºBTDC
10 33 56 79 102 125
0 20 40 60 80 100 120
Carbon Monoxide (ppm)
Engine Load (%) SPEED:1500 RPM IT(DIESEL):23ºBTDC
IT(POME):25ºBTDC
0 25 50 75 100 125
0 20 40 60 80 100 120
Carbon Monoxide (ppm)
Engine Load (%) SPEED:1500 RPM IT(DIESEL):23ºBTDC
IT(POME):28ºBTDC
(a) (b)
(c) (d)
Figure 5.12 Variation of CO2 emission with engine load for different CR and IT for neat POME run engine
5.4.2 Effect of Compression Ratio
The average values of CO emissions for POME at CRs of 16, 17, 17.5 and 18 are 53, 41, 41 and 33 ppm (Figure 5.11). The increase in CR reduces the cylinder volume, which in turn, increases the combustion temperature. This fact along with oxygenated biodiesel (POME), reduced the chances of forming fuel-rich zone, which is responsible for 38% reduction of CO emission, for an increase of CR from 16 to 18 (Rakopoulos et al., 2004). The same cause attributes the increase in the CO2 emission with the increase in CR (Figure 5.12). The average CO2 emissions recorded are 2.8, 2.7, 3.0 and 3.3% (by volume) for CR for all four CRs. The overall increase in CO2 emission is 18% with the increase of CR from 16 to 18. As seen in Fig. 5.13, the average NOX emission obtained for the CR of 16, 17, 17.5 and 18 are 73, 57, 51 and 42 ppm. Hence, for the POME run engine, the rise in CR causes an overall reduction of NOX emission by 43%. At high CR, the pressure and temperature during the compression stroke and at the primary stages of combustion increases. In addition, the lower ID of POME causes the combustion to complete a little earlier. As it is evident from Fig. 5.10, the majority of heat release of POME is performed near or before TDC. As a result the combustible products remained comparatively cooler atmosphere comparable to diesel throughout the expansion stroke. This fact slows down the NOX formation. The variations of HC emissions are shown in Fig. 5.14. The average HC emissions obtained are 16, 14, 13 and 10 ppm for POME. Therefore, HC emission drops by 37% via increasing CR from 16 to 18. The high
1 3 4 6 7
0 20 40 60 80 100 120
Carbon Dioxide (%)
Engine Load (%) DIESEL(CR:17.5)
CR(POME):16 CR(POME):17 CR(POME):17.5 CR(POME):18
SPEED:1500 RPM IT(DIESEL):23ºBTDC
IT(POME):20ºBTDC
1 3 4 6 7
0 20 40 60 80 100 120
Carbon Dioxide (%)
Engine Load (%) SPEED:1500 RPM
IT(DIESEL):23ºBTDC IT(POME):23ºBTDC
1 3 4 6 7
0 20 40 60 80 100 120
Carbon Dioxide (%)
Engine Load (%) SPEED:1500 RPM
IT(DIESEL):23ºBTDC IT(POME):25ºBTDC
1 3 4 6 7
0 20 40 60 80 100 120
Carbon Dioxide (%)
Engine Load (%) SPEED:1500 RPM
IT(DIESEL):23ºBTDC IT(POME):28ºBTDC
pressure and temperature in the compression stroke together with lower ID cause rapid burning of oxygenated POME and reduces HC, as reported in the literature too (Schmidt and Van Gerpen, 1996).
(a) (b)
(c) (d)
Figure 5.13 Variation of NOX emission with engine load for different CR and IT for neat POME run engine
(a) (b)
(c) (d)
Figure 5.14 Variation of HC with engine load for different CR and IT for neat POME run engine
0 40 80 120 160
0 20 40 60 80 100 120
Oxides of Nitrogen (ppm)
Engine Load (%) DIESEL(CR:17.5)
CR(POME):16 CR(POME):17 CR(POME):17.5 CR(POME):18
SPEED:1500 RPM IT(DIESEL):23ºBTDC
IT(POME):20ºBTDC
0 40 80 120 160
0 20 40 60 80 100 120
Oxides of Nitrogen (ppm)
Engine Load (%) SPEED:1500 RPM IT(DIESEL):23ºBTDC
IT(POME):23ºBTDC
5 36 67 98 129 160
0 20 40 60 80 100 120
Oxides of Nitrogen (ppm)
Engine Load (%) SPEED:1500 RPM IT(DIESEL):23ºBTDC
IT(POME):25ºBTDC
0 40 80 120 160
0 20 40 60 80 100 120
Oxides of Nitrogen (ppm)
Engine Load (%) SPEED:1500 RPM IT(DIESEL):23ºBTDC
IT(POME):28ºBTDC
5 10 15 20 25 30 35
0 20 40 60 80 100 120
Hydrocarbon (ppm)
Engine Load (%) DIESEL(CR:17.5) CR(POME):16 CR(POME):17 CR(POME):17.5 CR(POME):18 SPEED:1500 RPM
IT(DIESEL):23ºBTDC IT(POME):20ºBTDC
5 10 15 20 25 30 35
0 20 40 60 80 100 120
Hydrocarbon (ppm)
Engine Load (%) SPEED:1500 RPM IT(DIESEL):23ºBTDC
IT(POME):23ºBTDC
5 10 15 20 25 30 35
0 20 40 60 80 100 120
Hydrocarbon (ppm)
Engine Load (%) SPEED:1500 RPM IT(DIESEL):23ºBTDC
IT(POME):25ºBTDC
5 10 15 20 25 30 35
0 20 40 60 80 100 120
Hydrocarbon (ppm)
Engine Load (%) SPEED:1500 RPM IT(DIESEL):23ºBTDC
IT(POME):28ºBTDC
5.4.3 Effect of Injection Timing
The CO emission is the outcome of incomplete combustion of fuels, and hence, it is influenced by BSFC. For POME run engine, retarding (by 3º) and advancing (by 5º) the IT indicates a descent of CO emission by 15% and 26%, respectively (Figure 5.11). The results are clear from the BSFC values obtained at different ITs as particularized in Section 5.2.3 (Sayin et al., 2008). Lower is the BSFC, lesser will be the quantity of unburnt fuel particles and hence lesser will be the probabilities of CO emission. The results illustrate that advancement and retardation of IT cut the CO2 emission by 13% and 16%, respectively (Figure 5.12). The NOX emission study demonstrates that IT advancement causes an enlargement in NOX emission by 17% and 32% than IT retardation (Figure 5.13). As explained in the section 5.3.3, IT advancement increases PCP, which in the end rises peak temperature (Heywood, 1988). This is the reason of increase in NOX concentration through IT advancement.
The HC emission in the exhaust gas is the consequence of the incompletely burnt fuel particles (Figure 5.14). The advancements of IT cause average reductions of HC emissions by 5% and 3% than retardation. The advancement allows an early start of combustion, and the charge being compressed as the piston moves to TDC, has relatively higher temperatures.
Analyzed data show that, IT advancement increases average temperature by around 5%. This causes a reduction in the flame quenching layer thickness, leading to a lower HC emission (AbdAlla et al., 2002).