Short-term performance tests using crude palm oil (CPO) as fuel for a diesel engine showed CPO to be a suitable substitute, with a peak pressure about 5 per cent higher and an ignition delay about 3degrees shorter compared with diesel. Emissions of NO and CO were about 29 and 9 per cent higher respectively for CPO. However, prolonged use of CPO as fuel caused the engine performance to deteriorate. After 500 h cumulative running with CPO, the maximum power was reduced by about 20 per cent and the minimum brake specific fuel consumption (b.s.f.c.) was increased by about 26 per cent. Examination of the different parts after the engine was dismantled revealed heavy carbon deposits in the combustion chamber; traces of wear on the piston rings, the plunger and the delivery valve of the injection pump; slight scuffing of the cylinder liner; and uneven spray from the nozzles. The affected parts were installed in a new identical engine one by one to evaluate the performance of each respectively. Tests revealed that the main reason for engine performance deterioration was,valve sticking', caused by carbon deposits on the valve seats and stems. This resulted in leakage during the compression and power strokes and a reduced effective compression ratio and subsequently, affected the power and fuel economy. Valve sticking alone contributed about 18 and 23 per cent to the deterioration in maximum power and minimum b.s.f.c. respectively.
