08-08-2012, 10:50 AM
Non-edible oils and blends in Direct Injection Diesel Engines
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Introduction
Since the calorific value and Cetane number of the non-edible oils in their pure form are comparable to diesel oil, the changeover is considered relatively simple; however, the impediments are their high viscosity. In the light of this, the present study is conducted in order to investigate engine performance and the exhaust emissions using various non-edible oils as fuel, in pure form as well as their blends, in direct injection (DI) diesel engine. The primary aim is to arrive at a basic strategy that can be adopted for reducing emission levels using these fuels.
The basic strategies reported in the literature are: 1) Adaptation of the engine to the fuel by modifying engine to suit fuel properties (particularly its viscosity and Cetane number) by making engine adiabatic, changing lubricant/ coolant, lubrication system, increase injection pressure etc 2) Adaptation of the fuel to the engine by modifying physico-chemical properties by blending or trans-esterification. Utilizing these strategies in an appropriate way can lead to the most practical and economical methodology that can ease the required swift changeover from diesel to bio-derived oils.
Hydrocarbon Emissions
Hydrocarbon emission is low in the case of 100 % oil and its blend as compared to diesel at almost all loads. It decreases with increase in load up to full load indicating better fuel oxidation. At 220 Bar IP, the best performance with respect to HC emission in obtained in the case of all the fuels tested.
The Experiments
In the present investigation, ethanol, a bio-derivative, is used as a blender with various vegetable oils with primary aim of reducing viscosity and emissions. The volume of ethanol was restricted to 5 % in order to prevent expected deterioration of engine performance at peak load because of reduction of fuel heating value and cetane number, caused by addition of ethanol (heating value 22 ~ 25 MJ/kg).
Most pure vegetable oils have kinematic viscosity in the range of 30 to 40 cSt at 30 C, volumetric heating value in the range of 39 to 40 MJ/kg and cetane number in the range of 32 to 40 (Srivastava and Prasad, 2000).