Experimental Investigations of Combustion Chamber Heat Transfer in a Light-Duty Diesel Engine

Sammanfattning: This work concerned experimental studies of heat transfer in a light-duty diesel engine. Combustion is affected by several parameters, such as pressure, engine speed, mass of injected fuel and in-cylinder gas flow. These parameters are in turn affected by the combustion chamber geometry and fuel spray characteristics. At high load the exhaust heat was increased more than at high engine speed. Swirl was found to speed up the combustion event and increased heat loss to the piston cooling, but had no measurable effect on exhaust heat loss. Exhaust gas recirculation (EGR) diverts part of the exhaust gas and mixes it with intake air. The recirculated gas acts as a heat sink and reduces in-cylinder temperatures and thus, heat losses. The air-fuel ratio is another important factor. More air resulted in faster combustion while also increasing exhaust gas temperature. Altering the combustion chamber geometry affected both in-cylinder gas flow and mixing. A more open and shallow design was found to redistribute heat losses from cooling media to exhaust. The original injectors were proven to have a higher fuel flow than the two other configurations, but faster combustion and less heat in the exhaust was mainly found with the injectors with fewest holes. Hot exhaust gases could be more useful than hot cooling media, because that heat may be extracted and used to improve engine efficiency. This reduces fuel consumption, and consequently emissions of greenhouse gases, which contribute to global warming. The world energy demand is still increasing, and more natural resources are being used. Higher efficiency requires less fuel, and thereby reduces the impact on environment and humanity. The work was performed in a 4-cylinder light-duty diesel engine. Temperatures and mass flow measurements were performed in cooling media and exhaust gas. From these calculations were executed to find out the heat fractions emitted to each medium. Two combustion chamber geometries and three injectors were tested and compared with respect to their impact on combustion and heat losses.