Search Results

Aiming for improving fuel economy of vehicles, a new two-stroke gasoline engine utilizing stratified-charge auto-ignition has been designed and tested. The engine concept was to switch the combustion mode according to the engine operating load and speed, i.e., homogeneous-charge spark-ignition for the high-load range, homogeneous-charge auto-ignition for the mid- to low-load range, stratified-charge auto-ignition for the low-load low-speed range, and stratified-charge spark-ignition for idling. Using this engine concept, an experimental two-stroke engine was successfully operated free of irregular combustion throughout the range of operating loads. For small motorcycle applications, a great improvement in fuel economy and exhaust emissions was estimated from the experimental data.

The auto-ignition attracts researchers as an ultimate combustion method that could simultaneously reduce fuel consumption and NOx emissions. The authors have studied auto-ignition combustion in the two-stroke gasoline engines aiming at vehicle engine applications. However, our attempts were in an impasse with the onset of irregular combustion in the lower speed and the extremely lower load range. As a solution for this problem, this paper proposes a new auto-ignition concept, i.e. Stratified Charge Auto-Ignition (SCAI), which focuses on the thermal distribution and mixture formation in the combustion chamber. Visualization of the direct injection spray formation was conducted first, and then a combustion chamber design was determined by using a CFD simulation, so as to form a mixture at the hottest spot in the combustion chamber.

As a promising solution for the reduction of CO2 emission, the auto-ignition combustion is being intensively studied due to its potential for simultaneously decreasing CO2 and NOx emissions. On the other hand, Downsizing can also be a general solution for the CO2 emission. In case of four-stroke auto-ignition engines, however, there is a difficulty for the downsizing because of the limitation of specific power output. An auto-ignition two-stroke engine was examined on a scooter frame, for the combined potential of the Downsizing and the auto-ignition. The results are that fuel economy was improved by approximately 70% in ECE40 mode, as compared with the 60% larger, conventional four-stroke engine. An additional small catalyst sufficiently purified the exhaust emissions sufficiently to meet the Euro 3 level.