Brake thermal efficiency (B。T。E) variation with load at all C。R is shown in Fig。 3。 Almost similar (slightly lower) values of B。T。E are observed for CB10 and CB20 com- pared to diesel。 Only CB40 has lower B。T。E than others。 Higher B。S。F。C is a result of high fuel consumption at a particular engine load condition。 As brake thermal effi- ciency is the ratio of brake power to the product of fuel consumption and calorific value, higher B。S。F。C can be attributed to the reason of lower B。T。E for higher blends of biodiesel。 B。T。E increased for all blends with increase

Fig。 2 Variation of brake specific fuel consumption with load at compression ratio 15, 16, 17 and 18

Fig。 3 Variation of brake thermal efficiency with load at compression ratio 15, 16, 17 and 18

Fig。 4 Cylinder pressure variation with crank angle at compression ratio 15, 16, 17 and 18

Fig。 5 Variation of hydrocarbon with load at compression ratio 15, 16, 17 and 18

Fig。 6 Variation of carbon monoxide with load at compression ratio 15, 16, 17 and 18

Fig。 7 Variation of carbon dioxide with load at compression ratio 15, 16, 17 and 18

Fig。 8 Variation of oxides of nitrogen as NOx with load at compression ratio 15, 16, 17 and 18

in compression ratio。 Average increase in B。T。E for diesel, CB10, CB20 and CB40 is 14。43, 14。21, 16。44 and 13。56 %

respectively, is recorded when C。R is increased from 15 to 18。 Combustion chamber temperature in a diesel engine lies in the range of 1900–2050 °C。 With increase in compression ratio, temperature inside the cylinder increases。 High combustion temperature due to higher

C。R and increased amount of oxygen content in the fuel along with lower volatility of biodiesel blends may be the result of higher increase in B。T。E for biodiesel blends。 Cylinder pressure variation with crank angle (P-θ dia- gram) under full load@1500 r。p。m at all C。R is shown in Fig。 4。 Higher cylinder peak pressure along with shorter ignitiondelay(intermsofattainmentofpeak pressure

w。r。t crank angle) is observed for CB10 and CB20 than diesel。 This can be attributed to the betterintermixing of air-fuel mixture during the initial stage of combus- tion resulting in higher peak pressure near to T。D。C in the expansion stroke。 At C。R 15 diesel attained a peak pressure of 55。98 bar @ 11° A。T。D。C, whereas CB10 and CB20 attained a peak pressure of 57 and 56。7 bar respec- tively @ 8° A。T。D。C。 As biodiesel is an oxygenated fuel, the combustion reaction takes place at a greater rate due to the presence of excess oxygen, which in turn reduces the ignition delay resulting in early combustion for CB10 and CB20。 Cylinder pressure increased with increase in compression ratio。 Increase in cylinder pressure for diesel, CB10, CB20 and CB40 is 16。75, 17。04, 16。44 and

9。98 % respectively, is recorded when C。R。 is increased from 15 to 18。 At C。R 18 the peak pressure for diesel is attained @ 8° A。T。D。C, whereas for CB10 the peak pressure attained is @ 6° A。T。D。C。 This increase can be attributed to theriseincombustiontemperaturedue to increase in compression ratio resulting in better and early combustion。 For CB40, peak pressure attained in theexpansionstrokeislowerandfurtheraway from