EFFECTS OF USING PHASE CHANGE MATERIALS ON THE COLD START EXHAUST EMİSSİONS CHARACTERİSTİCS OF DIESEL ENGINES
During the last two decades, the diesel engine performance and drivability have significantly improved with the latest technologic developments. Nevertheless, one of the disadvantageous of diesel engines is related to the difficulties for starting at cold conditions, particularly in the conditions where the ambient temperature is near or below 0ºC. Additionally, the harmful exhaust emissions are also at significantly important levels during the cold start conditions. Most of carbon monoxide (CO) emissions from diesel engines are produced during the engine warm-up period. In order to improve cold start characteristics of diesel engines, many measures have been proposed, such as glow plugs and air heaters in air intake lines.
In this study, in order to increase the cold start performance and improve the exhaust emission characteristics of a direct injection diesel engine, phase change materials (PCMs) have been used.
PCMs have high heats of fusion and they can absorb latent energy before melting. During the phase change, temperature of PCMs remains nearly constant. In this study, a PCMs was used with the 45-51ºC melting temperature band in a heat exchanger. Hot water from an external source was circulated in the exchanger to carry out the experiments in the same conditions and was used as heat source in order to melt the PCMs.
Engine intake air has been passed through the exchanger before engine intake manifold. During the engine cooling period, the PCM in the produced heat exchanger have increased the cooling time period of engine intake air.
An experimental setup has been established to observe the cold start characteristics of the two cylinder diesel engine with and without using the produced exchanger. Temperature measurements from different points, CO exhaust emissions, engine speed and in cylinder pressure measurements have been used to evaluate the contribution of exchanger and increasing the intake air temperature by using the PCMs. The experiments have been carried out at different PCMs and ambient temperatures. The increase in the temperature of intake air at low ambient temperatures assists the engine cold start performance, decreases the starting time of engine and improves the engine exhaust emissions characteristics.
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