Some Investigations on Cold-Starting Phenomena in Diesel Engines

Abstract

In this paper are recorded the findings on the more fundamental aspects of cold-starting work carried out in the laboratory at Acton during the past three years. It deals with both the criteria of an ignition under cold-starting conditions and how these criteria may be met by some practical forms of starting aid. From available ignition delay data and measured compression temperature it has been possible to correlate, in order of magnitude, the variation of starting time with both cranking speed and ambient temperature. The increase in compression temperature and pressure during continuous cranking with fuelling is found to be due partly to sealing action of the injected fuel and partly to the increased compression ratio. The effect of the slow oxidation of the fuel carried over from the previous cycle has been investigated and found to be insignificant. From these basic considerations, the effects of engine design and operating variables on cold starting have been discussed. The principles and limitation of intake air heating as a starting aid (both by burner as well as by electrical heating), heater plug, and heating the injected fuel have been investigated. For the engine used, the lowering of minimum starting temperature is about 20°C (for a fixed cranking speed) when using a burner aid, while a further reduction of 2° to 3°C may be expected if electric heating is used. It is found that the main function of a heater plug is to provide a high-temperature ignition source rather than a heat source. The failure of the fuel heating system is due to excessive heat loss both before the fuel enters the chamber and to the chamber wall due to impingement when it enters the chamber.