Evaluation of the combustion process of directly injected methane in a rapid compression machine with a laser-based ignition system and an electrical ignition system

In order to reduce exhaust gas emissions, the application of lean operation in internal combustion engines has great potential. Experiments have been carried out in a rapid compression machine with directly injected methane comparing two laser ignition systems based on Nd:YAG lasers with an electrical ignition system. Three stratified extremely lean mixtures are ignited with up to 3 consecutive ignition pulses. This application-oriented investigation with the novel approach of combining laser ignition with a stratified charge in a rapid compression machine provides essential insights into the combustion process. The results highlight the advantages of laser ignition systems. The maximum pressure is increased by up to 9.5 %. The indicated work is increased by up to 16 % and cyclic variations are reduced by up to 35 %. The advantages increase as the mixture becomes leaner. A positive influence of multiple pulses can be observed as the ignition probability and the cyclic variations improve by up to 20 % per pulse and 25 % per pulse, respectively for the laser ignition. The evaluation shows that shorter pulse durations with a higher power achieve improved values for successful ignitions while longer pulses and a higher pulse energy achieve higher ignition probability values.