This document summarizes a study on the performance and exhaust emissions of a single cylinder diesel engine fueled with crude mahua oil. The study compared a conventional engine to an engine with a medium grade low heat rejection combustion chamber. The LHR chamber included an air gap insulated piston and liner. Testing was conducted at various injection timings and operating conditions of the crude mahua oil, including normal and preheated temperatures. The engine with the LHR chamber showed improved performance, lower smoke and higher NOx emissions compared to the conventional engine operated on crude mahua oil. The optimum injection timing was found to be 30 degrees bTDC for the LHR chamber compared to 32 degrees for the conventional engine.
5. Fig.2: Variation of brake thermal efficiency (BTE) with brake mean effective pressure (BMEP)
in conventional engine (CE) at different injection timings with crude mahua oil (CMO)
operation
Hence advancing of injection timing helped the initiation of combustion, when the piston was
at TDC. BTE increased at all loads when the injection timing was advanced to 32o bTDC in the CE at
the normal temperature of CMO.
Curves from Fig.3 indicate that engine with LHR combustion chamber with crude vegetable
oil operation at recommended injection timing showed improvement in the performance for the
entire load range compared with CE with pure diesel. High cylinder temperatures helped in better
evaporation and faster combustion of the fuel injected into the combustion chamber. Reduction of
ignition delay of the crude vegetable oil in the hot environment of the engine with LHR combustion
chamber improved heat release rates and efficient energy utilization. The optimum injection timing
was found to be 30o bTDC with engine with LHR combustion chamber with crude vegetable oil.
Further advancing of the injection timing resulted in decrease in thermal efficiency due to longer
ignition delay. Since the hot combustion chamber of engine with LHR combustion chamber reduced
ignition delay and combustion duration and hence the optimum injection timing was obtained earlier
with engine with LHR combustion chamber when compared with CE with the crude vegetable oil
operation.
7. Fig 3: Variation of brake thermal efficiency (BTE) with brake mean effective pressure
(BMEP)in engine with LHR combustion chamber at different injection timings with crude
mahua oil (CMO) operation
From Table.2, it is evident that CE with vegetable oil operation at the recommended injection
timing recorded drastically higher exhaust gas temperature (EGT) at full load operation compared
with CE with pure diesel operation. Lower and retarded heat release associated with high specific
energy consumption caused increase in EGT in CE. Ignition delay in the CE with different operating
conditions of vegetable oil increased the duration of the burning phase. Engine with LHR
combustion chamber recorded lower EGT at full load operation when compared with CE with
vegetable oil operation. This was due to reduction of ignition delay in the hot environment with the
provision of the insulation in the engine with LHR combustion chamber, which caused the gases
expanded in the cylinder giving higher work output and lower heat rejection. This showed that the
performance improved with engine with LHR combustion chamber when compared with CE with
vegetable oil operation. EGT at full load decreased with advancing of injection timing in both
versions of the combustion chamber with vegetable oil operation. Preheating of the vegetable oil
increased EGT marginally compared with normal vegetable oil in CE, while it decreased in engine
with LHR combustion chamber.
Table.2:
Performance Parameters of Peak BTE and EGT at full load operation at an injector opening
pressure of 190 bar
389
Injection
timing
(o bTDC)
Test
Fuel
Peak BTE (%) Exhaust gas temperature (EGT) at
full load operation (oC)
Combustion chamber version Combustion chamber version
CE LHR CE LHR
NT PT NT PT NT PT NT PT
27 DF 28 -- 27 -- 425 -- 475 ---
CMO 26 27.5 29 30 500 525 480 500
30 CMO -- -- 30 30.5 -- --- 400 380
32 CMO 28 28.5 -- -- 430 455 -- --