Starting Aid by Inlet Throttling in a Small Diesel Engine

A well-known phenomenon of the temperature rise due to throttling was applied to a starting aid in a small Diesel engine. Theoretical calculation of the charge temperature at the suction end was carried out for the various throttle ratios. The temperature rise above the ambient increases with the decrease in the mean pressure at the suction stroke and the increase in volumetric efficiency, reaching a maximum at a proper throttle ratio which depends upon the cranking speed. Throttling was performed by two means ; i.e., a throttle plate before the inlet valve and a special cam limiting the opening of the inlet valve to the later part of the stroke. The maximum temperature rise reaches theoretically 21°C in the former while 85°C in the latter. In a practical engine the minimum starting temperature was lowered about 15°C by applying the latter method, which shows an effective aid to cold-starting, but has a drawback of complicating the valve mechanism for the practical use.