Lean-burn combustion systems in spark ignitron engines: advantages and limitations

Spark-ignited internal combustion engines are in the use for over130 years (first example was presented by Otto in 1876). The engine development is directed to more power, better efficiency and lower emissions. Mixture formation and in-cylinder motion are the main parameters of the combustion process improvement. One of the effective methods of engine development is lean combustion. Application of lean-burn combustion systems in spark ignitron engines has been proposed many times. Such systems have several important advantages in comparison with conventional systems. Lean-burn combustion makes possible engine operation at high compression ratio, equivalent to high thermal efficiency and at low emission of toxic components of the combustion gases. Lean-burn combustion is also a subject of serious limitations, requiring remedial steps. General limitations are introduced by a fall of the reaction rate, equivalent to increased time of combustion. Lean-burn combustion introduces also changes to flame structure: it contributes with increased flame thickness and with a rise of quenching distance. These changes influence limit conditions of spark ignition. The only solution omitting this threat might be obtained by replacing of a spark ignition by another ignition system or by application of a spark ignition system with increased distance between electrodes and with much higher ignition energy. Typical solutions rationalizing lean-burn combustion in engines are discussed in the paper and some limit conditions highlighted..