The two-stroke engine, known for its small displacement and high performance, is space-efficient when installed in a vehicle. As such, incorporating two-stroke engines into HEVs is an effective way to reduce vehicle weight and optimize engine space. However, one downside is that the amount of unfired elements in the exhaust gas increases due to the air/fuel mixture being expelled into the exhaust system during the scavenging process. Moreover, combustion can become unstable due to the large volume of residual burned gases in the cylinder. To address these issues, we propose a two-stroke engine equipped with intake and exhaust valves that directly inject fuel into the cylinder.
In our first report, we presented an engine design and method that enable high scavenging efficiency and stable combustion in a two-stroke engine [1]. In this second report, we share the results of our research aimed at improving fuel efficiency and achieving low emissions, all while maintaining the high performance typical of a two-stroke engine.
To enhance fuel efficiency, the amount of burned gas was optimized by adjusting the timing and lifting the intake and exhaust valves. Lean combustion was achieved by leveraging the high temperature in the cylinder, utilizing its excellent ignitability. Additionally, it has been reported that THC emissions—a common issue in two-stroke engines—are reduced by preventing unburned gas from being expelled into the exhaust pipe through the adoption of in-cylinder direct injection.