Hawkins et al. [53] have conducted combustion studies on methyl and ethyl esters of degummed sunflower oil, maize oil, cottonseed oil, peanut oil, soybean oil, and castor oil. Fuel properties of the esters were very sim­ilar to each other, except the esters of castor oil which were much more vis­cous. The heating values of ethyl esters were also considerably lower. Engine results indicated that the power output for esters varied from 44.4 to 45.5 kW, with diesel delivering 45.1 kW. The brake thermal efficiencies were also slightly higher than diesel. High esterification yields (around 90%) must be obtained to avoid choking of injector tips. Further, sticking of injec­tor needles after a shutdown time of 48 h has been reported.

Fort and Blumberg [54] have tested a diesel engine with a mixture of cottonseed oil and ME of this oil. Results indicate that viscosity and den­sity increased whereas the heating value and the cetane number decreased, when the percentage of the cottonseed oil was increased in the blend. The durability test with 50-50% cottonseed oil and ME was terminated after 183 h of running the engine, because the engine was noisy. After disassembly, the engine indicated severe wear scouring and

TABLE 6.2 Comparison of Biodiesel Production by Acid, Alkali, and Enzyme

Acid-catalyzed Base-catalyzed

transesterification transesterification

heavy carbon deposits. But specific emissions and visible smoke char­acteristics of diesel fuel and esterified cottonseed oil were comparable.

Ziejewski and Kaufman [55] conducted a long-term test using a 25-75% blend of alkali-refined sunflower oil and diesel fuel in a diesel engine, and compared the results with that of a baseline test on diesel fuel. Engine power output over the tested speed range was slightly higher for this blend. At 2300 rpm, the difference was 25%. At 1800 rpm, the gain in power was 6%. The smoke level increased at a higher engine speed from 1 to 2.2 and decreased at a lower engine speed. Greater exhaust temperature was caused by a higher intake air temperature. The major problems experienced were:

1. Abnormal carbon buildup in the injection nozzle tips.

2. Injector needle sticking.

3. Secondary injection.

4. Carbon buildup in the intake port and exhaust-valve stems.

5. Carbon filling of the compression ring grooves.

6. Abnormal lacquer and varnish buildup.

Tahir [56] has determined the fuel properties of sunflower oil and its ME. The properties were favorable for diesel engine operation, but the problem of high viscosity (14 times higher than diesel at 37°C) of sunflower oil might cause blockage of fuel filters, higher valve-opening pressure, and poor atomization in the combustion chamber. Transesterification of sun­flower oil to its ME has been suggested to reduce viscosity of the fuel. The viscosity of ME at 0°C was closer to that of No. 2 diesel fuel, but below 0°C, it was not possible because of the pour point of — 4°C.

Pryor et al. [57] have conducted a short-term performance test on a small, test diesel engine using crude soybean oil, crude degummed soy­bean oil, and soybean ethyl ester. The engine developed about 3% more power output with crude legume soybean oil, but the development was insignificant with soybean ethyl ester. The fuel flow of soybean oil was 13-30% higher and for the ethyl ester it was 11-15% higher, depending upon the load on the engine. The exhaust temperature throughout the test was 2-5% higher for soybean oil and 2-3% lower for ethyl ester than the diesel fuel.

Clark et al. [58] have tested methyl and ethyl esters of soybean oil as a fuel in CI engine. Esters of soybean oil with commercial diesel fuel additives revealed fuel properties comparable to diesel fuel, with the exception of gum formation which manifested itself in problems with the plugging of fuel filters. Engine performance with esters differed little from the diesel fuel performance. Emissions of nitrous oxides for the esters were similar, or slightly higher than diesel fuel. Measurement of engine wear and the fuel injection test showed no abnormal charac­teristics for any of the fuels after 200 h of testing.

Laforgia et al. [59] has prepared biodiesel from degummed vegetable oil with 99.5% methanol and an alkaline catalyst (KOH). On engine performance, pure biodiesel and blends of biodiesel combined with 10% methanol had a remarkable reduction in smoke emissions. When the injection timing was advanced, better results were obtained.

Pischinger et al. [60] have conducted engine and vehicle tests with ME of soybean oil (MESO) 75-25% gas oil—MESO blend and 68-23-9% gas oil—MESO—ethanol blend. The fuel properties of the blend indi­cated a 6% lower volumetric calorific value of the ester, a drastic reduc­tion in kinematics viscosity, and a greater ethane number than that of gas oil. The engine results indicated about 7% higher BSFC with a mar­ginal difference in power and torque in comparison with gas oil. The smoke emission was much lower with ME.

Ali et al. [61] have observed that engine performance with diesel fuel—methyl soyate blends did not differ to a great extent up to a 70-30% (v/v) from that of diesel-fueled engine performance. There was a slight increase in NOx emissions with increasing methyl soyate con­tent in the blends at higher speeds but at lower speeds there was a quadratic trend with diesel fuel content.

Carbon monoxide emissions were very similar for blends up to 70-30% (v/v) diesel fuel—methyl soyate blends at any speed. Visible smoke decreased with increasing speed and methyl soyate content. More smoke was produced with neat diesel fuel at full load.