Direct injection diesel engine combustion diagnostics
The demand for the protection of the environment from air pollution and reduction of carbon dioxide has resulted in worldwide exhaust emissions regulations imposed on the diesel engines. Fortunately, diesel engine offers the best fuel economy and low emissions of carbon dioxide of most engines currently available. However, the engine's inherent drawbacks are that the engine is heavy, noisy, and expensive, in addition to producing significant level of particulates and nitrogen oxides emissions. The present research attempts to understand the combustion characteristics and emissions trade-off by experimental investigations of the diesel engine using a production Lister Petter 2.97 litres, four-cylinder, high-speed, direct injection diesel engine. The investigation involved the analysis of the in-cylinder pressure data, heat release rate calculation and exhaust gas measurements of various injectors having different nozzle geometry. The engine experiments cover both the investigation of the fuel injection and the engine operating parameters such as injection rate, nozzle geometry, the engine load and speed. The effects of each parameter on ignition delay, heat release rate, nitrogen oxides emissions, smoke density, and total hydrocarbon levels were investigated. Two complementary diagnostic techniques were employed in order to assist in understanding the injection characteristics. The first technique involved the imaging of the fuel sprays from the different injectors in a constant volume spray chamber using a CCD camera. The images were than process using a dedicated image processing software. The second technique involved the measurements of the fuel injection rates from the injectors using the Bosch Tube meter. A three-zone model was developed to determine the heat release rate of combustion. The cylinder pressure data was used to validate the model written in Matlab computer programme. The model is based on the principles of the First Law of Thermodynamics applied to the three zones, formed due to the fuel injection into the combustion chamber. The heat release rate profiles produced by the model were used to analyse the formation of pollutants that were measured in the exhaust gas. The results showed that injectors with large nozzle hole diameters produced high smoke levels, especially at high engine load conditions with small increase in NOx. These injectors also caused the sprays to impinged on the combustion chamber walls at high load conditions. On the other hand, injectors having small nozzle hole diameters produced high levels of NOx while the smoke emission levels were low. The effect of nozzle geometry has little significant on the emissions of THC.