In a joint project of FEV Motorentechnik and Ruhrgas AG, the design of stoichiometric and lean-burn Otto engines was optimized by selective modifications to the design and operating parameters to accommodate changing methane numbers (LPG addition to CNG). Of particular importance was knock-free engine operation at a low NOx output to meet the requirements of the German Clean Air Code while concurrently achieving both high efficiencies and mean effective pressures. Based upon the results obtained, concepts for the control of Otto-cycle gas engines to accept changing methane numbers were developed. The newly developed gas engine control device allows these concepts to meet the requirement of the German Clean Air Code with economically viable conditions while preventing engine knock. Furthermore, the test results show that dedicated Otto-cycle gas engines can meet the most stringent emission limits for commercial vehicles while maintaining high efficiencies.

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