02-06-2015, 03:19 PM
Definition
The physical and combustion properties of vegetable oils are close to petro-diesel fuel and in this context, vegetable oils can stand as an immediate candidate substitute for stored fuels. Vegetable oils are produced from processing of seeds of various plants and thus Renewable in nature. However due to inherent high viscosity and low volatility vegetable oils would pose problems such as fuel flow and poor atomization and constraining their direct use in engines without any modifications.
In the present investigation effect of supercharging is studied on the performance of a Direct Injection Diesel Engine with the use of untreated cottonseed oil. Performance of the engine is evaluated in terms of break specific fuel consumption, exhaust Gas Temperature and smoke Density. It is observed that when cottonseed oil is used as a fuel, there is a reduction in BSFC of about 15% when the engine is run at the recommended injection pressure and supercharging pressure of 0.4 bar g in comparison with the engine operation run under naturally operated condition.
Vegetable oils are mixtures of fatty acids-molecules that contain carbon, hydrogen, and oxygen atoms. The fatty acids present in it may be saturated, mono-unsaturated, or poly-unsaturated. The greater the number of the double bonds, the more easily the compound reacts with oxygen from the air and goes bad, as kitchen fats and oils do after months on the shelfs.
Intensive search is being carried out in developing diesel engine fuels and lubricants based on vegetable oils. Due to high viscosity of vegetable oils, they interfere with fuel jet penetration, atomization and results in higher fuel consumption and leaves gummy deposits on the engine components upon combustion.
Barsic et al. [1] studied the performance and emission characteristics of a DI naturally aspirated diesel engine when operated on 100%sun flower oil, 100%peanut oil and 50% (by vol.) mixtures of either sun flower oil or peanut oil with #2 diesel oil (i.e. diesel fuel with less than 0.01%sulphur by weight) and compared results with base line results obtained using #2 diesel fuel. They adopted a rotary fuel injection pump and with fuel flow adjusted to provide equal fuel energy input and observed that the engine power and thermal efficiency decreased slightly and emissions increased marginally. The attributed reasons were higher densities, higher viscosities, relatively lower heating values and thermal cracking of vegetable oil fuel droplets at elevated temperatures