Development of the XMv3 High Efficiency Cycloidal Engine

The demand for lighter, smaller, more efficient, and more powerful engines calls for a rethinking of the traditional internal combustion engine (ICE). This paper describes development progress of LiquidPiston's small rotary engine, the XMv3, which operates on a Spark-Ignited (SI) variant of its patented High Efficiency Hybrid Cycle (HEHC). This thermodynamic cycle, which combines high compression ratio (CR), constant-volume combustion, and overexpansion, has a theoretical efficiency of up to 75 percent using air-standard assumptions and first-law analysis. XMv3 displaces 70cc (23cc per each of three working chambers) and is gasoline fueled. The engine is simple, having only two primary moving parts, which are balanced to prevent vibration. The ‘X’ engine geometry utilized by XMv3 can be considered an inverted ‘Wankel’, retaining the traditional Wankel' rotary advantages of high power density and smooth operation, while also overcoming some of Wankel's inherent performance limitations. These include inflexible combustion chamber shape, and lubrication and emissions challenges. At this stage of development, XMv3 produces 3.2 bhp at 10,000 rpm and weighs 1.7 kg. Indicated mean effective pressure (IMEP) and friction mean effective pressure (FMEP) are 5.0 bar and 1.0 bar respectively. The maximum tested engine speed is 15,000 rpm. Preliminary durability studies show no wear problems after 1 hour of running continuously at full load. This paper details both analytical and experimental studies carried out on the XMV3 prototype, including variation of compression ratio, combustion chamber shape, spark plug type, rotor port geometry, and supercharging. With further development, the engine is expected to produce 5 horsepower at up to 15,000 rpm, weighing in at < 1.5 kg.

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