Testing Spark Ignition Engines Converted to Operate on JP-8

Abstract

Testing was performed on commercially available 1 kW spark ignition generators that were modified to operate on JP-8 and other heavy fuels. This approach is motivated by the US Military mandate that only one fuel, JP-8, be taken to the battlefield, and the increased electrical demands at the squad and platoon level. Small units require a portable power source that can meet their energy demands, particularly battery charging. While diesel engines can operate on JP-8, their weight limits their mobility at the platoon level. Spark ignition engines have better power density at the 1 kW level, but must be modified to burn logistically available fuel. Multiple approaches have been pursued to enable these engines to operate on JP-8. In the present study, the longer term effects of three approaches are examined and compared to an unmodified spark ignition generator operating on gasoline. These approaches include A) chemically altering the fuel as it flows to the engine to create a higher octane mixture, B) modifying the carburetor and using ether starter fluid to preheat the cylinder, and C) electrically heating the cylinder while modifying the fuel system for direct injection. The different generators were characterized by oil sampling at 15 hour intervals. Oil testing included flash point, viscosity, wear elements, and additives. Oil quality and emissions vary with load. Different approaches to conversion perform better at different loads. It was determined that multiple start-stop cycles with no load resulted in fuel dilution of the lubricating oil in several of the modified engines. Response varied with some of the modified engines maintaining low fuel dilution similar to the gasoline fueled engine while others indicated 15–20% fuel in the oil. During operation at full load, the modified JP-8 burning generators showed 3–5% fuel dilution in the oil while the unmodified gasoline generator was less than 1%. These experiments illustrate the challenges in developing portable, reliable JP-8 burning power sources. While further research and development is needed in each approach, it was shown that converted spark ignition engines are a promising path to portable logistic power. Oil analysis was shown to identify future research and development efforts to improve this technology.