Abstract
Two-stroke engines are light weight, simple construction, high power to weight ratio and low cost to manufacture. The main problems with two-stroke engine are emissions and low fuel-efficiency. This research use a two-stroke engine with crankcase scavenging also adopting an exhaust reed valve and lamellar intake, accommodating a high pressure direct injector as used in the latest 2 stroke gasoline engines. The traditional spark plug is replaced by a jet ignition device. The main chamber fuel is however CNG. The jet ignition device is a pre-chamber accommodating a gasoline GDI injector operated with CNG and an 8 mm racing spark plug. The jet ignition pre-chamber is connected to the main chamber through calibrated orifices. The CNG is injected after the exhaust port closes. The GDI injector operated with CNG introduces a slightly rich amount of fuel in the pre-chamber. The spark plug discharge initiates the pre-chamber combustion that then propagates to the main chamber though multiple jets of high energy partially burned hot combustion products that quickly ignite the main chamber mixtures. Lubrication is performed by selective oil injection where needed rather than oil mixed with fuel. This study has shown good modelling results with efficiencies well in excess of 30% in the area of best engine operation, and reduced energy penalties when changing load and speed. KEYWORDS – Two-stroke engine, direct injection, jet ignition, natural gas, emissions, performances