Effect of ignition condition and fuel octane number on knock intensity in a small 2-stroke engine

The internal combustion engines are widely used on automotive transportation for its high energy storage system efficiency and the economic benefits. The 4-stroke engine has dominated all other forms to date, because the Otto cycle is much simpler to comprehend. However, the significant benefits such as, less pumping work and friction, lighter construction of 2-stroke engine, helped with applications which appreciate the simplicity and power density as well as meet the emission regulations. The disadvantages of the 2-stroke engine mainly caused by the lack of sufficient scavenging process, which limited its trapping efficiency. Also, the overlap of the intake and exhaust phases results in charge short-circuiting, more fuel consumption and high unburned hydrocarbon emissions. For the reason above, it is difficult for 2-stroke engines to realize stoichiometric combustion and unable to use three-way catalyst to control emissions. The residual exhaust gas in the cylinder makes the spark ignition application give rise to incomplete combustion and higher coefficient of variation. Hence, it is imperative to confirm the effect of spark ignition strategies (ignition position, ignition timing conditions) on a portable small 2-stroke engine with complex in-cylinder gas flow distribution. In this study, we discussed the effect of spark ignition strategies on a small 2-stroke engine. Both the in-cylinder combustion characteristics, the emission characteristics and the flame propagation process are observed by an optical 2-stroke engine with loop-scavenging. Also, in terms of the fuel properties, the gasoline, dimethyl carbonate/gasoline blend fuel and the primary reference fuel are used to investigate the influence of ignition method on knock intensity with different octane number. To optimize the ignition position, the computational fluid dynamic (CFD) analysis by using CONVERGE is adopted to predict the fresh air-fuel and residual exhaust gas concentration distributions. Through the experimental and CFD results, the potential possibility of combustion improvement on 2-stroke spark ignition engine is to be realized by the optimization of ignition strategies.