Gasoline compression ignition approach to efficient, clean and affordable future engines

The worldwide demand for transport fuels will increase significantly but will still be met substantially (a share of around 90%) from petroleum-based fuels. This increase in demand will be significantly skewed towards commercial vehicles and hence towards diesel and jet fuels, leading to a probable surplus of lighter low-octane fuels. Current diesel engines are efficient but expensive and complicated because they try to reduce the nitrogen oxide and soot emissions simultaneously while using conventional diesel fuels which ignite very easily. Gasoline compression ignition engines can be run on gasoline-like fuels with a long ignition delay to make low-nitrogen-oxide low-soot combustion very much easier. Moreover, the research octane number of the optimum fuel for gasoline compression ignition engines is likely to be around 70 and hence the surplus low-octane components could be used without much further processing. Also, the final boiling point can be higher than those of current gasolines. The potential advantages of gasoline compression ignition engines are as follows. First, the engine is at least as efficient and clean as current diesel engines but is less complicated and hence could be cheaper (lower injection pressure and after-treatment focus on control of carbon monoxide and hydrocarbon emissions rather than on soot and nitrogen oxide emissions). Second, the optimum fuel requires less processing and hence would be easier to make in comparison with current gasoline or diesel fuel and will have a lower greenhouse-gas footprint. Third, it provides a path to mitigate the global demand imbalance between heavier fuels and lighter fuels that is otherwise projected and improve the sustainability of refineries. The concept has been well demonstrated in research engines but development work is needed to make it feasible on practical vehicles, e.g. on cold start, adequate control of exhaust carbon monoxide and hydrocarbons and control of noise at medium to high loads. Initially, gasoline compression ignition engines technology has to work with current market fuels but, in the longer term, new and simpler fuels need to be supplied to make the transport sector more sustainable.