This study compares combustion of Jet-A in an indirect injection (IDI) compression ignition engine and a direct injection (DI) compression ignition engine at the same load and speed. The Jet-A was blended (75Jet-A): 75% Jet-A and 25% Ultra Low Sulfur Diesel # 2 (ULSD) by mass. Both engines had a load of 4.5 bars Indicated Mean Effective Pressure (IMEP) and were run at 2000 RPM.

The IDI engine configuration was very similar to that used in High Mobility Multipurpose Wheeled Vehicles (HMMWV).

The research showed that combustion pressure in the IDI engine separate combustion chamber was 81 bars versus 71 bars in the main combustion chamber showing high gas-dynamics losses at transfer passages while in the DI engine the peak pressure reached 65 bars.

The Apparent Heat Release Rate (AHRR) in the IDI engine has both the premixed and diffusion stage combined while in the DI classical combustion there are visible both the premixed and diffusion burn stages. The results show that in both engines there is a Low Temperature Heat Release (LTHR) region before top dead center (BTDC). The mass averaged instantaneous temperature reached 1750 K in the direct injection engine being the same for both fuels and for the IDI engines reached 1700 K in main combustion chamber and 1950 K in the separate combustion chamber for both fuels.

The study showed that there are significant differences in the shape of the AHRR between the engines, nevertheless, the Jet-A has very similar combustion characteristics with ULSD in both combustion systems making a viable option as a substitute fuel to use in High Mobility Multipurpose Wheeled Vehicles (HMMWV).

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