Browse Publications Technical Papers 2018-01-0885

Preliminary Development of a 30 kW Heavy Fueled Compression Ignition Rotary ‘X’ Engine with Target 45% Brake Thermal Efficiency 2018-01-0885

This paper presents initial progress in the development of LiquidPiston’s ‘X4’, a 30 kW heavy-fueled rotary compression ignition engine prototype. The X4 is the newest version of the unique rotary ‘X’ engine architecture. This development is partially funded by the Defense Advanced Research Projects Agency (DARPA), with broad dual-use civilian / military applications including UAVs, generators, and for propulsion. The 30 kW size may be of significant interest in the automotive application as a range extender for Electric Vehicles. The final performance objectives of the program are aggressive: 45% brake thermal efficiency; > 1 hp / lb power-to-weight; and the engine is targeted to fit within a 10”x10”x10” box weighing <40lbs.
A first prototype engine “core” has been designed, analyzed, prototypes, and completed its initial testing. This stage of development has focused on verifying the structural integrity of the main engine components including the shaft, bearing, rotor and gears, as well as the function of the engine’s gas seals, at the high pressures (in excess of 100 bar) expected of a CI engine.
Motoring results from initial testing show reasonable agreement to 1D performance modeling. The engine has exceeded the mechanical verification target, demonstrating stable operation with in-cylinder pressures of 150 bar. This paper will summarize the design and preliminary experimental results achieved in the first year of development, including:
  • 1D thermodynamic Modeling
  • Design considerations of the main engine components including the crank shaft, bearings, gears, combustion system
  • Initial Testing to verify system integrity
With the X4 “core engine” structure and gas seals validated, future work is discussed, which will include performance optimization to achieve power and efficiency objectives.


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