Effect of Plasma-Assisted Ignition on Combustion and Emission Characteristics of Two Stroke Engines with Different Fuels

The 2-stroke opposed piston engine(2OPE) is attracting attention for its potential to achieve higher theoretical thermal efficiency due to its unique combustion chamber design. 2OPE has twice stroke/bore ratio compared to that of conventional 2-stroke engines, which reduces cooling losses, thereby enhancing output power density. However, like other 2-stroke engines, the 2OPE faces challenges such as fuel short-circuiting and scavenging loss, which historically limited the development of 2-stroke engines. Due to the insufficient scavenging process, the residual gas remains higher than 4-stroke engine. Although the residual gas helps maintain higher in-cylinder temperature that accelerate the fuel evaporation, the reduced fresh air supply leads to incomplete combustion and increasing carbon monoxide (CO) and hydrocarbon emission (HC). Under that condition, the minimum ignition energy increases sharply and leading to slower combustion. Plasma-assisted ignition (PAI) is considered as a promising solution to enhance the ignition intensity, particularly under conditions such as homogeneous charge compression ignition or the exhaust gas recirculation, where combustion speed is significantly reduced. Non-equilibrium PAI generate active OH radicals that accumulate from pulse to pulse during a train of repetitive pulses. This increased radical production initiate chemical chain reaction, ultimately leading to ignition. Compared to spark ignition, PAI has advantages such as the volumetric ignition and less heat loss. In this study, we investigate the effectiveness of plasma-assist ignition in both a single cylinder 2-stroke engine and a 2OPE. Combustion characteristics, knocking intensity, and CO and HC emissions are evaluated under different ignition and fuel type condition. The findings provide insights into the potential of plasma-assisted ignition application in 2-stroke engines to achieve the enhancement of combustion efficiency.