An Experimental Study on the Factors Affecting Ethanol Ignition Delay Times in a Rapid Compression Machine 2019-01-0576

Ignition delay, using a rapid compression machine (RCM), is defined as the time period between the end of compression and the maximum rate of pressure rise due to combustion, at a given compressed condition of temperature and pressure. The same compressed conditions can be reached by a variety of combinations of compression ratio, initial temperature, initial pressure, diluent gas composition, etc. It has been assumed that the value of ignition delay, for a given fuel and at a given set of compressed conditions, would be the same, irrespective of the variety of the above-mentioned combinations that were used to achieve the compressed conditions. In this study, a range of initial conditions and compression ratios are studied to determine their effect on ignition delay time and to show how ignition delay time can differ even at the same compressed conditions. Experiments were carried out at two compression ratio conditions (11.7 and 17.1) for stoichiometric ethanol-air mixtures over a temperature range of 800 K - 875 K at 20 bar pressure. With the help of optical images, in addition to the pressure traces, the combustion characteristics for the abovementioned conditions were analyzed and compared. Another factor that was determined to be important in consistent ignition delay measurements was the cleanliness of the combustion chamber and some discussion on the suggested protocol is included.