Direct Injection Diesel Engine
Published on Jan 16, 2016
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.  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
Goering et al.  studied properties of different vegetable oils and modified hybrid fuels for automotive applications and reported that vegetable oils have acceptable cetane numbers (35-45), high viscosity (~50cSt), high carbon residue, high flash points (220-2850C) & pourpoints(-6 to 120C) and appreciable heating value (88-94% of diesel fuel), low sulphur content (<0.02% by wt.) and contains gumming impurities. Akor et al.  in their investigations detailed the production and energy balance characteristics of the palm oil system and provided information on the physical and chemical nature of the palm oil and their derivatives. They also observed satisfactory performance of conventional diesel engines and encountered little lower efficiencies with palm oil diesel fuel mixtures.
Bhattacharyya et al.  conducted review on use of vegetable oils as fuels for internal combustion engines. They reported that a the major differences between diesel fuel and vegetable oil included, for the later, the significantly higher viscosities and moderately higher densities, lower heating values, rice in the stoichiometric fuel/air ratio due to the presence of molecular oxygen and the possibility of thermal cracking at the temperatures encountered by the fuel spray in the naturally aspirated diesel engines.
The exhaust emission characteristics of diesel engines operated with vegetable oils have been studied by many researchers. However, review of research papers by Quick , Barsic  and  revealed that with the use of vegetable oil based fuels, the harmful exhaust emissions particularly sulfur related compounds and carbon monoxide are considerably reduced as copperas with diesel operation.
Methanol along with jatropha curcas oil was used in a C.I.engine in dual – fuel mode operation by Ravi et al.  .the methanol was carbureted with different jet openings and observed that rate of pressure rise and peak pressures were high with neat jatropha oil operation. However with methanol induction in the deal-fuel mode operation the rate of pressure rise and peak pressures were reduced considerably. In the literature review carried out by the authors it is observed that no information is available on the performance of a DI diesel employing vegetable oils as fuel under supercharged condition.
It is will known that supercharging improves combustion process of diesel engines . Increase in pressure and temperature of the engine intake reduces ignition delay resulting in a quiet and smooth operation with a lower rate of pressure rise. Thus supercharging encourages the use of low grade4 fuels in diesel engines. The increase in intake air temperatures reduces the unit air charge and also reduces thermal efficiency moderately for the loss and inter-cooling is not necessary except foe highly supercharged engines. Present paper deals with the effect of supercharging on the performance of a DI diesel engine with the use of untreated cottonseed oil.
Direct injection type diesel engine is chosen with the following specifications for experimentation purpose.
Type : A V 1, Vertical cylinder.
Make : Kirloskar
No. of cylinders : One
Cooling : Water Cooling
Charging : Natural
Rated power : 3.68 kw@1500rpm
Bore : 80 mm
Stroke : 110 mm
Following set of experiments are carried out:
1. Constant speed (rated speed) performance tests maintaining steady jacket water temperature of 55C under naturally aspirated conditions at the recommended fuel injection pressure (180 bar) with diesel fuel. This test is chosen as base line test for comparison.
2. Constant speed performance tests maintaining steady jacket water temperature of 55C with cotton seed oil as fuel under naturally aspirated conditions at the recommended fuel injection pressures. Viz., 180 bar.
3. Constant speed performance tests maintaining steady jacket water temperature of 55C under supercharged condition (super charging pressures kept at 0.2, 0.3, & 0.4 (g) at the recommended fuel injection pressure.
4. The physical properties (as detailed below) of cotton seed oil are determined and employed in the experiments:
Sp gr: 0.911
D.C , shunt dynamometer (swinging field) is adopted for loading purpose. A two-stage reciprocating air compressor is used for high-pressure air supply. A suitable surge tank is fabricated to ensure constant of air. Nisalco make (Japan) smoke mater is used to measure smoke density in hertridge smoke units.
RESULTS AND DISCUSSION:
The test results obtained in the above experiments are discussed below.
The recommended fuel injection pressure of the engine under consideration is 180 bar.
Effect of supercharging can be observed in fig. 1, for different supercharging pressures at the recommended fuel injection pressure. It is evident from the fig. That as the supercharging pressure is increased the BSFC is gradually lowered and the lowest values of BSFC are observed for supercharging pressure of 0.4 bar g. variation of exhaust Gas temperature with BMEP is plotted in fig. 2 at an injection pressure of 180 bar for different supercharging pressure. The exhaust temperature are lower at a supercharging pressure of 0.4 bar g indicating lower exhaust gas losses supporting the lower BSFC values observed in fig. 1 with this supercharging pressure.
For comparison purpose BSFC values of the engine run with diesel fuel under naturally aspirated condition employing an injection pressure of 180 bar g and BSFC values of engine with cottonseed oil operation at the same injection pressure and at a supercharging pressure of 0.4 bar g are shown in fig.3. The fig. also includes the variation of BSFC when the engine is run with cottonseed oil without supercharging. It can be observed that the B S G C values in case of cotton oil without supercharging are on the higher side compared to diesel operation under naturally aspirated condition.
Ali et al.  in their review paper also reported similar observation quoting the work of pryor et al.  who conducted the experiments on the 3- cylinder, 2600 series ford tractor engine with 100% crude soybean oil and # 2 diesel fuel (i.e. diesel fuel with less than 0.01 % sulfur by weight). It was observed that the power outputs of the engine running on these two fuels were more or less the same but the BSFC with 100% crude soybean oil was 11-13% greater fig. that the BSFC with cottonseed oil under supercharged operation (supercharge pressure of 0.4 bar g) is very close to that of diesel operation under natural aspiration.
It can therefore be concluded that supercharging is essential when we want to adopt untreated vegetable oils for developing the power with a low specific fuel consumption compared to diesel operation.
1. With increase in supercharging pressure the performance of the engine is gradually improving while maintaining the recommended injection pressure with cottonseed oil as fuel. There is a reduction of about 15% in BSFC at full load with a supercharging pressure of 0.4 bar g compared to naturally operated condition.
2. Supercharging is essential when we want to adopt untreated vegetable oils for developing the power with a low specific fuel consumption compared to diesel operation.
3. Percentage reduction in smoke density is more as the supercharging pressure is increased and engine performance with untreated vegetable oils can be regarded as eco-friendly operation
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