Abstract
The engines in hybrid-electric vehicles (HEVs) combine the best features of the internal combustion engines with electric motor and can significantly improve fuel economy without sacrificing performance. Albeit HEVs are primarily propelled by ICEs, like conventional vehicles, the electric motors are used to assist the engines in driving conditions where ICEs are least efficient. Since conventional ICEs are usually designed to provide sufficient power for the vehicle´s maximum speed, the ICE in a hybrid vehicle can be of a much smaller size.
This paper focuses on the numerical analysis of a new type of energy converter based on a two-stroke, free-piston compression ignited engine employing uniflow scavenging. The development of numerical model was addressed to the device consisting of a block with a double-end cylinder and four exhaust valves at each end. The air flow was supplied through two belts, each including twelve intake ports. Compression ignited air-fuel mixture at one end pushes the piston assembly towards the other end, where the second piston compresses an air- fuel mixture and the operation cycle continues.
The KIVA-3V code coupled with a detailed chemistry approach was used to evaluate the combustion efficiency and emission formation in this engine. The comprehensive chemical kinetics (70 species, 306 reactions) for diesel oil surrogate was used to achieve efficient lowemissions engine operation in conventional Diesel and HCCI-like combustion modes. Engine design and spray parameters, such as fuel injection timings and spray included angles, were varied to optimize the engine´s operation in terms of indicated efficiency and exhaust mixture composition. Differences between the combustion modes are outlined and explained using parametric (CO and emissions) -T maps.
Keywords:Two-stroke engine, free-piston, detailed chemistry, diesel oil surrogate, CFD modeling