THE OPTIMAL MIXING RATIO OF DIESEL-LPG DUAL FUEL IN A COMMONRAIL DIESEL ENGINE FOR PICK-UP TRUCK

Abstract

The Diesel-LPG dual fuel system is interesting in combustion emission, engine performance, and economic viewpoints. The injection of LPG gas in compensating diesel reduction during engine operation is studied in this research. The 2.5 L four-stroke, four-cylinder diesel commonrail engine, model 4jk1-TC, was modified with a port injection system for LPG so that LPG gas is injected precisely into the intake manifold of the engine. The engine performance test was carried out on the water-brake engine dynamometer to measure the essential parameters for calculating the engine performance with controlled environmental parameters, such as intake air temperature, inlet-outlet cooling water temperature, and cooling water mass flow rate. The experiments were carried out with 100% diesel baseline, 10% diesel reduction, and 30% diesel reduction. Within each diesel reduction condition, the experiment was performed with three variations of LPG gas injection mode G1, G3, and G5 to systematic measurement in constructing LPG injection mapping with engine speeds of 1500, 2000, 2500, and 3000 rpm.

According to the systematic study, the results could be analyzed to acquire optimal conditions for LPG injection with possible diesel reduction to maintain the engine performance varied with engine speed. The normal idle speed of a diesel engine is approximately 750 rpm. In the operating range of an engine speed from idle to 1500 rpm, the engine must be run only by diesel. The engine speed was increased from 1500 to 2000 rpm, and the engine was able to operate with 10% diesel reduction and LPG mode G1 injection. However, in these operating conditions, increasing LPG injection did not obtain any good result, such as engine pinging occurred. The higher engine speed is similar to actual running on the highway, the engine speed from 2200 to 3000 rpm can reduce more diesel obtaining 30% diesel reduction which LPG injection was increased to G3 to maintain the engine performance, and higher power was gained from the engine in comparison to the conventional diesel fuel.