Improvements in the engine performance, efficiency, scavenging, and emission characteristics of a modified two-stroke-cycle engine with the poppet valves and gaseous-fuel direct-injection system are described. In previous papers, SAE
901664 [
1]
* and
920180 [
2], in which the scavenging characteristics were mainly investigated, the modified two-stroke-cycle engine was based on a production four-stroke-cycle engine. The base engine intake valve was used as scavenging valve, with a shroud installed for preventing the short-circuiting charge loss. As Shown in the previous results, considerable improvement of the scavenging efficiency was obtained. While a gasoline fuel carburetion system was used in the earlier engine [
1], [
2], the present engine used a propane gas direct-injection system, with the purposes of further decreasing fuel short-circuiting loss and also improving combustion preparation characteristics in terms of fuel atomization, vaporization and mixing with air. The gaseous fuel injection system used in the present test is composed of an electromagnetic controlled in-cylinder gas sampling valve and its electronical control system for measuring gas composition converted to the purpose of gaseous fuel injection. With the injection system, the fuel injection timing and duration time, using signal pulses for 360 crank angle degrees Per revolution can be controlled at will.
The results of the experimental test and analysis showed a little higher engine power with the same engine speed and the same scavenging characteristics than values acheved in the previous gasoline-powered engine tests. Also, comparing the measured in-cylinder pressure indicator diagrams between gasoline and gaseous fuel supply, showed possibilities of improvements in terms of smaller combustion pressure variation, higher peak pressure, and faster burning rate. Additionally, improvements in specific fuel Consumption with direct injection were verified over the test and analysis range examined.