The conventional internal combustion engine or clones of its mode of working will be with us for quite some time to come. At the same time, the demand for higheroutput efficiencies, greater specific power output, increased reliability, and everreduced emissions will continue to rise in intensity. There is an increased need also, whether for environmental, economic, or resource conservation reasons, to operate on a multitude of natural and processed gaseous fuels. Of course, there is much continuing research and development being expended worldwide to provide further improvements, often through making incremental progress toward achieving the desired goals. It is evident that a main effort needed is through improvements to better understanding and controlling the relatively complex physical and chemical processes of combustion in the engine environment. Many of the remedial technologies that have been successfully developed over the years were, until relatively recently, largely the product of empiricism, with the rate of progress remaining rather insufficient to fulfill the demanding long-term objectives. These, in addition to achieving high efficiency, minimum pollutant emissions, and high specific power output, need to include the capacity to respond automatically to variations in the fuel quality without losses in output, efficiency, or reliability.