Gasoline Combustion with Future Fuels

This paper describes the demands and potentials of current and future gasoline combustion systems regarding the fuels gasoline, natural gas, and Hydrogen. At first, fuel specifications that are crucial for the spark ignition process are compared. These are compared with the requirements of the combustion system. Potentials for the compensation of power loss, efficiency improvement and emission reduction using alternative fuels are discussed taking into account fuel-specific properties. While full load drawbacks with natural gas compared with gasoline can be reduced to less than 5% by combustion system tuning, Hydrogen operation with port injection leads to reductions of about 25 to 30%. These drawbacks can be compensated with boosting where both methane and Hydrogen are qualified due to their burning characteristics. Compared with λ=1 operation especially Hydrogen offers efficiency benefits of up to 30% in a wide mapping range due to quality control. Here, the combustion at relative air-fuel ratios of 2 - 2.5 is nearly NOx-free. The combination of lean combustion and boosting permits to achieve indicated mean effective pressures of about 15 bar (peak pressure limited) combined with indicated specific fuel consumption close to 200 g/kWh and indicated NOx emissions lower than 0.5 g/kWh. Direct injection will lead to further improvements in full load performance. The results which are based upon engine tests show the possibility to realize combustion systems that can serve different fuels without or with only minor modifications. An optimum flex-fuel concept, however, can be achieved with Variable Compression Ratio (VCR).