Results and Discussion: Neat Palm Biodiesel Run Engine
5.3 Combustion Analysis
engine performance using biodiesel and thereby utilizing amount of heat produced in advanced manner. At 20°, 23°, 25° and 28ºBTDC, the mean temperatures at no load conditions are 128.6ºC, 131ºC, 135 ºC and 134ºC whereas 249ºC, 264ºC, 262ºC and 262ºC at full load conditions.
is due to the drop of cylinder volume with the increase in CR. Side-by-side, with the rise of CR, the air inside the cylinder gains more heat during compression stroke and injected fuel starts burning instantly but uniformly. As a result, at higher CR, smoother combustion is obtained for POME than diesel. However, at CR of 16, the clearance volume expands, which lowers the heat of compression, thereby causing local and irregular combustion for POME.
(a) (b)
(c) (d)
Figure 5.7 Variation of cylinder pressure with crank angle at 100% load for different CR and IT for neat POME run engine
It is seen from Fig. 5.8, that the average peak cylinder pressures obtained at CR = 16 are 55, 58, 58 and 61 bar; whereas PCPs observed at CR = 18 are 67, 68, 68 and 75 bar for the four ITs for POME run engine. The average increase in PCP for POME with the increase in CR from 16 to17, 17 to 17.5 and 17.5 to 18 are 5, 6 and 8% respectively. With the rise in CR, the cylinder volume gets reduced, and this increases temperature and pressure in compression stroke. As a result, the fuel burns with far more intensity and elevates the pressure further at TDC. This is also the reason behind the drop of ID for POME with the raise of CR (Figure 5.9). At higher CR, the warmer environment inside cylinder speeds up the commencement of combustion thereby reducing the ID. The average IDs for POME at CR=16 are 15.33, 17.67, 17.67 and 18.33º crank angle (CA) whereas 13.17, 14.67, 15.50 and 16.33ºCA of IDs obtained at CR=18. The average cut of IDs with the rise in CR from 16 to17, 17 to 17.5 and 17.5 to 18 are 4, 3 and 7% respectively.
10 25 40 55 70 85
320 340 360 380 400
Cylinder Pressure (bar)
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 25 40 55 70 85
320 340 360 380 400
Cylinder Pressure (bar)
Crank Angle (deg.CA) LOAD:100%
SPEED:1500 RPM IT(DIESEL):23ºBTDC
IT(POME):23ºBTDC
10 25 40 55 70 85
320 340 360 380 400
Cylinder Pressure (bar)
Crank Angle (deg.CA) LOAD:100%
SPEED:1500 RPM IT(DIESEL):23ºBTDC
IT(POME):25ºBTDC
10 25 40 55 70 85
320 340 360 380 400
Cylinder Pressure (bar)
Crank Angle (deg.CA) LOAD:100%
SPEED:1500 RPM IT(DIESEL):23ºBTDC
IT(POME):28ºBTDC
The CR variation, from 16 to 18 affects NHRR of POME (Figure 5.10). The effects of reduced IDs are more prominent here especially from Fig. 5.10(c) where the comparison with base diesel data is performed by testing POME at 23ºBTDC. The increase in CR results an early start of ignition for POME, which later reduced the premixed combustion phase. The effect is further prominent at full load condition where the NHRR is high because of warmer environment. The reduction of the premixed combustion phase and the increase in the diffused combustion is similarly observed in literature for various blending of waste cooking oil with diesel as compared to neat diesel (Muralidharan et al., 2011).
(a) (b)
(c) (d)
Figure 5.8 Variation of PCP with engine load for different CR and IT for neat POME run engine
5.3.3 Effect of Injection Timing
Figure 5.7 shows that IT advancement causes the fuel to start burning early and gets more time to burn completely. As a result, at higher IT, the P-θ curve spreads more and boosts further by the lower ID of POME. The similar trends are observed at other loads also. This phenomenon has a noticeable effect on the PCP curves too (Figure 5.8). For the four CRs studied, the average PCPs varied from 55, 59, 63 and 67 bar to 61, 65, 69 and 75 bar for 20ºBTDC and 28ºBTDC, respectively. The IT retardation shows a 1% reduction in the PCP whereas advancement causes 2% and 9% increase in PCP. During advancement, the larger combustion period allows the fuel to burn for a longer duration to give higher PCP. The IT
50 60 70 80 90
0 20 40 60 80 100 120
Peak Cylinder Pressure (bar)
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
50 60 70 80 90
0 20 40 60 80 100 120
Peak Cylinder Pressure (bar)
Engine Load (%) SPEED:1500 RPM IT(DIESEL):23ºBTDC
IT(POME):23ºBTDC
50 57 64 71 78 85
0 20 40 60 80 100 120
Peak Cylinder Pressure (bar)
Engine Load (%) SPEED:1500 RPM IT(DIESEL):23ºBTDC
IT(POME):25ºBTDC
50 60 70 80 90
0 20 40 60 80 100 120
Peak Cylinder Pressure (bar)
Engine Load (%) SPEED:1500 RPM IT(DIESEL):23ºBTDC
IT(POME):28ºBTDC
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.