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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.

From a present perspective, environmental protection occupies a position of supreme importance, especially with regard to pollution levels due to motor vehicles. To reduce environmental pollution, the limits for pollutant emissions from cars have been gradually lowered over the past few decades in the type approval procedure and series inspections. The emissions characteristics of vehicles in use are, however, crucial for the pollution level. To check the emission characteristics of vehicles in actual traffic and to monitor observance of the endurance requirements of the exhaust gas regulations, it is absolutely essential to introduce an informative and practical field inspection system on a legal basis. That means that emission measurements have to be carried out in the complete licensing test on the roller-type tester on the basis of the type approval procedure, and this to be done on vehicles with differing mileages from private customers.

Due to the disturbing increase in forest damages over the last few years in the Federal Republic of Germany, the government decided von 21 July and 10 October 1983 to adopt the U.S. exhaust gas emission regulations for private motor vehicles. These regulations are considerably more stringent than the present European regulations, and it was confirmed on 19 September 1984 that they will come into force on 1 Januar 1989. Purchasers of low polluting cars meeting the existing U.S. standards prior to 1989 will be released from the road tax by two to ten years depending on the vehicle size. For the time being the final step has thus been taken in an environmental politics development which has been going on for fifteen years and has resulted in Germany lagging considerably behind other highly industrialized countries such as Japan and the USA.