| Difficulties in the cold starting of diesel engines, particularly at low ambient temperatures, include long cranking periods and the emission of high concentrations of hydrocarbons that appear as white smoke. Such problems are not desirable in commercial engines, and in military engines particularly in the field. The goal of this investigation is to find a strategy to reduce the cranking period and reduce the fuel consumed during the cold start transient. The approach taken in this investigation is mainly experimental, supported by detailed analyses of the thermodynamic, dynamics and combustion processes in subsequent cranking cycles and determine the conditions that result in firing, incomplete combustion and misfiring. The engine used is equipped with a common rail fuel system, variable geometry turbocharger and swirl control mechanism.;The concept, behind the new strategy is to re-circulate the exhaust gases produced from a misfired cycle during cranking into the fresh charge of the next cycle. Since most of these gases are hydrocarbons, this strategy is called Hydrocarbon Recirculation (HCR). The effect of different HCR rates on the number of cranking cycles was determined. The experiments were conducted at 0°C with engine and fuel tank soaked for 8 to 10 hours.;The data collected include in-cylinder pressure, exhaust gas temperature, engine speed, hydrocarbon and oxides of nitrogen emission concentrations, needle lift, exhaust pressures before and after the turbocharger, intake manifold pressure, and common rail pressures. The analysis of data indicated the effect of increasing HCR on the number of cranking cycles at different fuel delivery rates. Increasing HCR at any fuel injection rate reduced the number of cranking cycles. However, it was found that there is an optimum rate of fuel delivery & HCR for reducing the number of cranking cycles. It is recommended that later work be conducted to find the effect of HCR and fuel injection rate on combustion instability. |
