DESIRABLE PROPERTIES OF CI ENGINE FUELS : IKRAM SINGH HARIKA B TECH 6 MAE 1Y A2305408048 DESIRABLE PROPERTIES OF CI ENGINE FUELS Desirable Characteristic: Desirable Characteristic Ignition Quality Volatility Starting Characteristic Smoking and odor Viscosity Corrosion and Wear Handling Ease DIESEL: DIESEL Produced from fractional distillation of crude oil between 200 °C (392 °F) and 350 °C (662 °F) at atmospheric pressure Contains 75 % saturated hydrocarbons and 25 % aromatic hydrocarbons Boiling point – (180 – 300) degree C TWO TYPES Light diesel fuel – molecular wt. 170 approx and low viscocity Heavy Diesel Fuel – molecular wt. 200 approx and high viscocity Diesel Knock: Diesel Knock It is a hammering or pinging sound caused due to higher ignition delay period of the fuel resulting in high pressure differentials and violent gas vibration occurring near the beginning of combustion in CI engines. Slide 6: Diagram illustrating the Effect of Ignition Delay on the Rate of Pressure Rise in CI Engine Ignition Quality: Ignition Quality It is a measure of ability of a fuel to ignite promptly after injection, thus ensuring a progressive smooth burning and easy starting. Measured in terms of delay period. The shorter the delay period, the better the ignition quality. Has influence on cold starting ,engine roughness and compression ratio. CETANE RATING: CETANE RATING Cetane number or CN is actually a measure of a fuel's ignition delay . It is defined as % by volume of normal cetane in a mixture of normal cetane and a- methyl naphthalene which has the same ignition characteristic ( ignition delay ) as the test fuel when the combustion is carried out in standard engine under specified operating conditions. Note – Since ignition delay is the primary factor in controlling the auto ignition in CI engine. It is reasonable to conclude that knock should be directly related to ignition delay of the fuel REGULAR HIGH PERFORMANCE 40 55 41 42 43 44 45 CETANE NUMBER RANGE 50 51 52 53 54 VOLATILITY: VOLATILITY Should be sufficiently volatile in the operating range of temperature to produce good mixing and combustion. Lower range of volatility than SI engine fuels. Lower volatility leads to carbon deposits over the injector orifice. Starting Characteristic: Starting Characteristic Fuel should have high volatility to form a combustible mixture readily Fuel should have a high cetane rating so that the self ignition temperature is low Corrosion and Wear: Corrosion and Wear Should not cause corrosion and wear before and after combustion. Caused due to sulphur , ash and carbon residue. Viscosity : V iscosity Viscosity is "thickness" or "internal friction". More viscous than SI engine fuels. Affects atomization of the fuel and operation of high pressure fuel pumps. High viscosity low atomization (large size droplets) and vice versa. Handling ease: Handling ease Fuel should be a liquid that will readily flow under all conditions that are encountered Measured by pour point and cloud point of the fuel. The fuel should also have high flash and fire point. Flash point – lowest temperature at which it can flow to form a ignitable mixture. Fire point – Defined as the temperature at which the fuel continues to burn after being ignited.