Effect of Thermal Insulation on the Performance and Emission Characteristics of a CNG-Diesel Dual Fuel Engine

摘要

In recent years, the issues of steadily increasing fuel cost, decreasing petroleum reserves, air pollution and market competitiveness have motivated the search for alternative fuels for diesel engines. Many studies have reported that exhaust emissions from diesel engines can be reduced by applying new combustion methods which are capable of mitigating the formation of combustion regions that are favorable for the generation of harmful emissions. One of the methods to reduce the exhaust emissions in diesel engines is to use the dual fuel combustion (DFC) mode with alternative clean fuels such as compressed natural gas with thermal insulation on the engine components. Diesel-compressed natural gas dual fuel low heat rejection engine (LHR) system is studied for the improved efficiency and for reduced emissions. Engine components, which are exposed to the combustion, are coated with Magnesia stabilized zirconia (MgO-ZrO_2) to make the engine a low heat rejection one. Diesel is used as pilot fuel and is injected into the combustion chamber at a rated opening pressure of 200 bar and at a rated injection timing of 23°bTDC. CNG is supplied to the engine through the intake manifold. Experimental results show that the thermal insulation has a significant impact on the combustion process that led to improvements in performance and emission characteristics of the test engine under dual fuel mode. Peak cylinder pressure at rated load condition for Low Heat Rejection Dual Fuel (LHR DF) is found to be about 5% higher than that of uncoated dual operation (UC DF). Total specific fuel consumption is observed to be about 10% lower for the LHR dual fuel engine along with a significant reduction in carbon monoxide, unburnt hydrocarbon and smoke opacities in the order of 21%, 49% and 44% respectively at rated load and rated rpm of the test engine.