Performance of JP-8 in a Small Bore Indirect Injection Diesel Engine for APU Applications

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SAE 2012 World Congress & Exhibition






Recent legislation entitled “The Single Fuel Forward Policy” mandates that all vehicles deployed by the US military be operable with aviation fuel (JP-8). Therefore, the authors are conducting an investigation into the influence of JP-8 on a diesel engine's performance. The injection, combustion, and performance of JP-8, 20-50% by weight in ULSD (diesel no.2) mixtures (J20-J50) produced at room temperature, were investigated in a small indirect injection, high compression ratio (24.5), 77mm separate combustion chamber diesel engine. The effectiveness of JP8 for application in an auxiliary power unit (APU) at continuous operation (100% load) of 4.78bar bmep/2400rpm was investigated. The blends had an ignition delay of approximately 1.02ms that increased slightly in relation to the amount of JP-8 introduced. J50 and diesel no.2 exhibited similar characteristics of heat release, the premixed phase being combined with the diffusion combustion. The maximum combustion pressure remained relatively constant for all blends, 71.7bar for diesel and increased slightly by 0.68bar for J50, with the peak pressure position being delayed by 0.3CAD for the J50. The instantaneous volume-averaged gas combustion temperature reached 2263K for all blends; displaying a 0.8CAD delay in the position of the maximum temperature and retaining the higher temperature for a longer duration for J50. The heat flux in the engine cylinder exhibited comparable maximum values for all blends (diesel: 2.17MW/m2, J50: 2.16MW/m2). The cylinder heat losses were at a minimum during combustion before TDC with increased convection losses at TDC for all fuels and the beginning of the power stroke. The BSFC for diesel no.2 was 257.4(g/kW*hr.) and decreased by 2% for J50. The engine's mechanical efficiency remained relatively constant for all blends at 75.6%. Taking into account each fuel's corresponding density, the engines' overall efficiency increased with the addition of the JP-8 by 3% for J50 vs. diesel. This engine investigation demonstrated that up to 50% JP-8 by weight in diesel fuel can be injected and burnt in this small bore indirect injection diesel engine at a residence time of approximately 5ms from the start of injection, while maintaining the engine's overall efficiency. The study validates JP-8 as a valid source for power generation in a small bore IDI engine based on its combustion characteristics. The next stage of research will be an in depth emissions investigation.