The US military is looking to bolster fuel efficiency by creating a so-called "super engine" that runs on one type of fuel and can power a number of vehicles, including ground transport, generators, and small unmanned aerial vehicles (UAVs).
The US Army Research Laboratory (ARL) has been working on this task since the Department of Defense established a Single Fuel Forward policy in the late 1980s. The policy supported the use of a kerosene-based fuel called JP-8 to reduce the logistical burden involved in transporting and supplying different sources of energy to vehicles in combat areas and other locations, according to the Army.
Over the years, researchers have faced compatibility issues between the different engines, the Army said. Its research began with the use of turbine engines, but has now moved on to exploring the use of combustion engines.
Two international contractors inspect a sample of JP-8 fuel in Kuwait in 2010. The Army hopes to use the fuel as the basis for a "super engine" that can power a number of ground and air vehicles, as well as generators using this fuel.
(Source: US Army Sgt. David Reardon, 1st Sustainment Brigade Public Affairs, US Army)
Incompatibility issues are chiefly in engine lubrication, large variation in Cetane numbers -- or the measurement between the start of fuel injection and the start of engine ignition or combustion -- and the fact that none of the engines that use JP-8 are designed and calibrated for the fuel, said Dr. Chol-Bum Kweon, acting team lead of the Engines Team of ARL’s Vehicle Technology Directorate, in a press release.
The main reason for these issues is that there is not enough information readily available about the specific combustion characteristics associated with the use of JP-8 in intermittent combustion engines, Kweon added.
The opening of a new lab this summer, the ARL Combustion Research Laboratory, should help speed up this research, particularly with respect to fuel spray and combustion, two critical areas key to the creation of a JP-8 engine. According to Kweon:
Fuel spray liquid penetration, quenching, vaporization, and mixing characteristics must be precisely understood to properly design combustion chambers and fuel injection systems because a fundamental understanding of fuel spray and combustion is essential in optimizing combustion processes of JP-8 -- fueled engines to improve fuel efficiency, engine performance, and reliability.
ARL’s Combustion Research Laboratory is a state-of-the-art, high- temperature and high-pressure combustion chamber that contains a combination of high temperatures up to 1,000 Kelvin and high pressure up to 150 bar. These metrics can simulate the operations of a real engine, minus its fluid motion aspect. The lab gives scientists a realistic proving ground for, in particular, uninterrupted spray and combustion processes that allow for the study necessary to create a JP-8 fuel-injection engine.
In addition to supporting the development of a JP-8 engine, researchers will also use the lab to test the performance of heavy fuel injection systems for diesel, bio, and synthetic fuels, as well as assess the impact of fuel properties on spray and combustion processes on engine performance and efficiency.
Researchers also can determine the impact of older fuel-injection systems on engine performance and fuel efficiency, especially for the Army’s ground vehicles, and evaluate various iterations of JP-8 fuels being developed throughout the DoD, Kweon said, going on to explain: "This laboratory has a unique capability to assess the various JP-8 surrogate fuels and to compare the results with the combustion mechanisms developed by various universities and government lab or atories."
All of this work to develop a universal combustion mechanism for JP-8 supports a trend across the US military to create more energy efficiency, and find alternative and better sources and uses of fuel. Other efforts include the Navy’s development of a biofuel made of seawater; the Air Force’s use of vortex surfing -- or flying planes in tight formation so they can draft off each other -- to conserve fuel; as well as other Army projects such as developing more fuel-efficient electricity generators.