Abstract
Investigations on a dual-fuel compression ignition engine have been carried out for many years in the Department of Internal Combustion Engines and Automobiles in Technical University of Radom. The fuel system was modified to allow combustion of fuels traditionally used in S.I. engines having high octane and low cetane numbers.
Basic investigations were carried out using a stationary one-cylinder 1HC102 engine with direct injection to the combustion chamber located in the piston having cubic capacity Vs = 0,98 dm3, power rating N = 11 kW at n = 2200 rpm, compression ratio = 17. Two fuels were applied in the reported investigations - methanol and propane-butane mixture. In both cases, diesel fuel was used to initiate ignition. Due to low cetane numbers of both fuels, as it was mentioned earlier, author decided to use a pilot quantity of diesel fuel to provide ignition. Such system of fuelling and ignition does not require radical modification of the standard compression ignition engine. In both cases, the modification of fuel system consisted in connecting to the engine a delivery system for main fuel; no other modifications of the standard engine were necessary. Acceptance of diesel fuel pilot ignition conception brings also the combustion system nearer the HCCI (Homogenous Charge Compression Ignition Engine) system, which is believed to be very promising due to benefits resulting from emission reduction and overall efficiency improvement.
At the beginning of investigations, two regulation parameters have been optimised considering: maximum engine torque, maximum overall efficiency and emission of exhaust gases. They have been volume of ignition diesel oil dose and injection timing of this dose. After this, some investigations of standard diesel engine and modified one have been carried out. Test of engines consisted in preparation of load characteristics of specific energy consumption as well as CO, NOx, HC and smoke emissions. The histories of the pressure inside combustion chamber have been registered during this test. These histories let to calculate ignition delay, rate of pressure rise and maximum combustion pressure. The knocking combustion in dual fuelled engine has been described as well. The results of investigations of dual fuel and standard engines have been compared.
The results of investigations show that:
- The dual-fuel C.I. engine for both main fuels can achieve torque values comparable with standard fuelled engine, or even higher, shoving at the same time higher overall efficiency in the range of maximal load.
- The emissions of CO, NOx, HC and level of smoke are lower or very similar to dual fuel engine in comparison with standard fuelling.
- The analysis of combustion parameters shows that elimination of knock combustion in dual fuel engine is possible by retarding of injection timing of the diesel fuel pilot dose.
Keywords:Dual-fuel compression ignition engine, exhaust emission, combustion parameters, knock.