Abstract
Keywords: dual-fuel compression ignition engine, LPG
Investigation on dual-fuel compression ignition engine was carried out for many years in the Department of Internal Combustion Engines and Automobiles in Technical University of Radom. The standard fuel injection system of a compression ignition engine was modified to deliver second fuel into the engine intake manifold. During the inlet and compression strokes, this fuel forms a homogenous mixture with air. Ignition of this mixture is initiated by the injected dose of diesel fuel.
Such combustion system solution is close to the HCCI (homogeneous-charge compression ignition) system that is considered to be the best future solution (Takatsuto et al. 1998). It is worth to mention that the described fuelling conception has many advantages, such as:
easiness of compression ignition engine adaptation to combustion fuels having high octane and low cetane ratings;
easiness of engine starting (using diesel fuel);
improvement of engine overall efficiency;
lower harmful emissions;
possibility of application of various fuels (gasoline, alcohols, LPG, natural gas etc.) that until now were applied to spark ignition engines,
easy way of regulation and control of combustion process beginning.
Pertinence of this approach seems to be reasonable and confirmed by many publications that present results of investigations carried out in Poland and abroad (Kusaka et al. 1998; Ogawa et al. 1998; Furutani et al. 1998; Stelmasiak, 2001; Stelmasiak et al. 2001).
Basic investigation was carried out using a stationary one-cylinder 1HC102 engine having cubic capacity Vs = 0,98 dm3, with direct injection to the combustion chamber located in the piston, compression ratio = 17, power rating N = 11 kW at the engine speed n = 2200 rpm. Till now, the effect of several fuels on basic engine operating parameters and emissions was analysed in investigation. The following fuels were applied:
methanol evaporated in an evaporator and delivered in the gas phase into the intake manifold,
methanol injected into the intake manifold in the liquid phase,
ethanol injected into the intake manifold in the liquid phase,
propane-butane mixture (LPG) evaporated in an evaporator and delivered in the gas phase into the intake manifold.
The paper presents results of preliminary investigation on the engine fuelled with LPG, injected into the intake manifold in the liquid phase, for two versions injection systems for the ignition diesel fuel dose: the first - with traditional injection pump and the second - with a common rail system.
The following is to be said for such conception:
expected improvement of filling the cylinder as a result of cooling the air charge in the process of LPG fuel evaporation,
expected lowering of combustion temperature that favours lower NOx emission and higher engine overall efficiency,
precision of controlling the quantity of LPG dose as well as possibility of synchronisation between the LPG injection process and stages of the inlet valve opening,
expected prevention of self-ignitions occurrence and knock combustion of LPG
- air mixture (as a result of lower circulation temperature).
The paper presents results of investigation on both engine versions obtained from load characteristics for the engine speed n = 1800 rpm. Two values of injection timing of the pilot dose were applied: ai1 = 10°BTDC and ai2 = 20°BTDC. The results were compared with characteristics obtained for standard fuelling.