Utilisation of vegetable pure plant oil and crude oil in diesel engines

23.2.1 Introduction

Early in the research stage CJO was considered to be suitable as a fuel oil based on its visual properties. The greatest difference between CJO and diesel oil is in viscosity. The high viscosity of CJO may contribute to the formation of carbon deposits in Compression Ignition Engines (CIE). Incomplete fuel combustion results in reduced engine life. Reducing the viscosity of CJO oil by preheating or dilution with diesel fuel was studied in engine tests.6,24 To investigate the suitability of CJO oil as alternative fuel and examine emissions, two tests of performance and exhaust gas emission, and a long-term durability test of CIE in a direct injection (DI) engine were conducted. In performance and exhaust gas emission tests, JO10 (blend of 10% CJO and 90% diesel) was similar to diesel fuel. Its oxygen content is an advantage in improving combustion. Exhaust gas emission increased slightly because its slightly higher viscosity influences fuel atomisation. JO10 is a promising alternative fuel because its performance and exhaust gas emission are similar to diesel fuel. JO100 gave lower performance and higher emission compared to diesel fuel because of its high viscosity. Using JO100 the engine was difficult to operate. The long-term durability test indicated that JO10 resulted in operational problems including increased exhaust gas emission (HC, particulate matter), injector coking, piston and liner erosion. Maintenance frequency would be increased substantially including changing or cleaning of the injector nozzles at 125 hour intervals, thus increasing the cost of operation. Dilution of lubricating oil and friction caused by ring sticking and deposits in the combustion chamber would reduce the lifetime of engine components. The main concern is the fuel quality and composition. The content of phosphorous compounds in JO10 was found to be significant affecting the combustion process and exhaust emission. A degumming process to reduce the phosphorous level is therefore required to improve the fuel quality of CJO.

Diesel engines can be operated on either PPO or biodiesel. The biodiesel process increases the cost of production as many processes are needed, whereas PPO only needs degumming to decrease phosphorous content and deacidification to decrease acid number. Potential resources of PPO in Indonesia include coconut, palm and jatropha as they are tropical plants with a high population throughout the country. Various PPOs have been investigated.7,8 Test fuels include pure coconut oil (PCO), pure palm oil (PPaO), pure jatropha oil (PJO)9 and diesel fuel for comparison. Each PPO was blended with diesel fuel with composition 50%-volume and heated to 60°C, to decrease the viscosity by 1/10. Trials using a small DI diesel engine for 17 hours endurance tests under various operating conditions were conducted according to engine test bed procedures for DI diesel and engine injector nozzle coking test. PPOs are characterised by high viscosity, low volatility and low energy content. All PPOs had higher brake specific fuel consumption (BSFC) before the endurance test by comparison with diesel fuel, but at the end of the test all PPOs had BSFC similar to diesel fuel due to decreased friction between engine components. However combustion of PPOs was not as complete as that of diesel fuel because of poorer spray characteristics, evidenced by low CO2 and high UHC, carbon monoxide (CO), O2 and opacity emissions. The phosphorus content, unsaturated fatty acid content and low combustion quality of PPO result in higher engine deposits than for diesel fuel. Even though the PPOs had been degummed the residual phosphorous content contributed to deposit formation. Deposits from PPOs were between 140% and 290% more than from diesel. However PPOs exhibited anti-wear properties on the plunger and injector due to the lubrication effects of the fatty acid content. PCO had the best anti-wear property of the test fuels.

Further investigation of the combustion and exhaust gas emissions of a DI CIE using Jatropha curcas L. oil as CJO (JO) and PJO/Degummed Jatropha Oil (DJO) was done.10 Of all the tested fuels, DJO10 was found to be closest to diesel fuel in performance, exhaust gas emission and its combustion process (ignition delay).

In addition a study of combustion of Jatropha curcas L. oil (crude, degummed, fatty acid methyl ester) as a fuel in a DI diesel engine was conducted.11,12 The summary of conclusion drawn from the experimental data was as follows:

• JO100 and DJO100 have low cetane indexes and very high viscosity. Lower engine performance and high exhaust gas emission were found. However, these fuels can be used in emergencies.

• Blends of JO10 and DJO10 improve engine performance and reduce exhaust gas emissions at low engine load. However, nitrogen oxides (NOx) emission tends to increase.