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This paper describes the successive stages needed to develop a lean-burn natural gas engine. A wide optimization was undertaken with the view to power commercial medium duty vehicle able to meet the 2005 proposals with the European MVEG cycle. PSA Peugeot Citroen DJ5TED 2.5 Liters displacement Direct Injection Diesel engine was chosen to be converted to natural gas Spark Ignition engine. On the basis of findings from simulation using the KMB computer code, combustion chambers of three different shapes were selected, meeting specific air flow motion criteria. After fitting sparkplug and ignition system providing high-energy required under lean operation, the chamber shape showing the best emissions-consumption trade-off was selected from engine bench tests. Then, after turbocharger matching, optimizations were carried out on lean and stoichiometric mixture in order to ensure excellent exhaust emissions and output performances.

Going from the example of the urban traffic in Europe, where the car use in town areas generally do not exceed 50 km/day, a series hybrid vehicle with light and compact thermal engine as an auxiliary power unit (APU) is demonstrated to be a promising concept. The paper describes such a configuration in base of a developed two-stroke engine with electronically controlled gasoline direct injection. The injection system is characterized by a high-pressure modulation obtained in base of the water hammer effect, which can be accurately adapted for a wide load and speed range of the engine. In this assembly the engine has extremely small dimensions and a dry weight of 8 kg, requiring a place which do not disturb the functions of the basic electric vehicle. The performances are convicting, the CO2 emission being reduced 3 times in comparison with a series four-stroke engine for the same car type, with an autonomy of 340 km and with a maximum speed of 100 km/h.