29-12-2012, 06:40 PM
Performance of direct-injection off-road diesel engine on rapeseed oil
1Performance of direct-injection.pdf (Size: 286.72 KB / Downloads: 60)
Abstract
This article presents the comparative bench testing results of a naturally aspirated, four stroke,
four cylinder, water cooled, direct injection Diesel engine operating on Diesel fuel and cold pressed
rapeseed oil. The purpose of this research is to study rapeseed oil flow through the fuelling system,
the effect of oil as renewable fuel on a high speed Diesel engine performance efficiency and injector
coking under various loading conditions.
Test results show that when fuelling a fully loaded engine with rapeseed oil, the brake specific fuel
consumption at the maximum torque and rated power is correspondingly higher by 12.2 and 12.8%
than that for Diesel fuel. However, the brake thermal efficiency of both fuels does not differ greatly
and its maximum values remain equal to 0.37–0.38 for Diesel fuel and 0.38–0.39 for rapeseed oil.
The smoke opacity at a fully opened throttle for rapeseed oil is lower by about 27–35%, however, at
the easy loads its characteristics can be affected by white coloured vapours.
Oil heating to the temperature of 60 8C diminishes its viscosity to 19.5 mm2 sK1 ensuring a
smooth oil flow through the fuel filter and reducing the brake specific energy consumption at light
loads by 11.7–7.4%. Further heating to the temperature of 90 8C offers no advantages in terms of
performance. Special tests conducted with modified fuel injection pump revealed that coking of the
injector nozzles depends on the engine performance mode. The first and second injector nozzles that
operated on pure oil were more coated by carbonaceous deposits than control injector nozzles that
operated simultaneously on Diesel fuel.
Introduction
In relation with a fast depletion of crude oil resources of the earth and increased
market prices of mineral Diesel fuel (DF), investigations have been intensified over the
last few years in order to examine the technical properties of Vegetable Oils Methyl
Esters (VOME) [1,2] and vegetable oils [3–6], including Rapeseed Oil (RO) [7–10].
The main purpose of the usage of renewable fuels comes from the urgent concern about
rapidly growing ambient air pollution, especially in the urban areas. Polluted air is one
of the reasons for climate changes that provoke frequent hurricanes, heavy rains and
floods having negative impact on the environment and people health. Using vegetablederived
fuels for direct-injection Diesel engine fuelling reduces the carbon monoxide
(CO) and hydrocarbons (HC) emissions by approximately 10% and unburned carbons
© by up to 52% [11]. Therefore, vegetable-based renewable fuels are becoming more
popular in Germany, Austria, France, Italy, Czech Republic and other countries.
Experimental apparatus and methodology of the research
Experiments were conducted on completely commissioned four cylinder, four stroke,
naturally aspirated, water-cooled, 59 kW direct-injection Diesel engine D-243 with splash
volume VlZ4.75 dm3, bore of 110 mm, stroke of 125 mm and compression ratio 3Z16:1.
The fuel was delivered by an in line fuel injection pump through five holes injection units
into a toroidal type compression-ignition combustion chamber in a piston head. The fuel
injection pump was adjusted to the initial fuel delivery start at 258 before top dead centre
(BTDC). The needle valve lifting pressure for all injectors was set to 17.5G0.5 MPa.
To maintain the necessary oil flow the engine fuelling system was modified by means of
installing two joined in parallel fine porous fuel filters, non-return valve and an electrical
thermometer. The non-return valve was installed to reduce fuel pulsations resulting from
overruns of RO and improve measurements accuracy. Fuel was fed to the injection pump
with an electrical rotor transfer pump. The fuel returning from the injection pump line was
connected to the transfer pump, whereas the returning tube from the injection units was
inserted directly into the fuel meter vessel. The oil was heated in the heat exchanger
connected to the engine cooling system. Heating temperature of the oil was handled with
the water tap by changing the flow rate through the heat exchanger.
To obtain the baseline parameters, the engine was operated on Diesel fuel grade C first.
Load characteristics were taken at fixed loading modes and constant crankshaft
revolutions of 1400, 1600, 1800, 2000 and 2200 minK1. After load characteristics were
taken from the engine performance on Diesel fuel, similar experiments with crude
rapeseed oil were conducted over the same range of engine loads and revolution
frequencies.
Test results of fuel delivery system
When operating on pure rapeseed oil, one of the main problems is linked with the
increased oil viscosity that may result in aggravation of fuel flow through the system and
thus lead to a drop in engine power. Because experiments were started with ordinary
fuelling system, the increased flow pressure of viscous RO crashed the filter container and
damaged the paper micro-fiber layer of radial vee-shaped filter element (Fig. 2b). As it
became clear later, such construction of filter container was liable to be fractured because
of a large number of round holes made on its body that apparently affected its strength
(Fig. 2a). Therefore such filters could not withstand increased oil pressures. In order to
eliminate this problem, the only reinforced fuel filters, as shown in Fig. 2c, were used for
further experimentations.
The engine test results and analysis
Because of a considerable number of test results, it was decided to examine the data
obtained at the minimum 1400 minK1 revolutions, the maximum torque regime
1800 minK1 and rated 2200 minK1 speed mainly. Other results that reflect engine
performance characteristics at the intermediate crankshaft revolutions 2000 and
1600 minK1 can be taken into account as supplementary measures for better
interpretation.
Fig. 5 presents the Diesel engine performance map with contours of constant brake
specific fuel consumption (bsfc) as a function of brake mean effective pressure (bmep) and
crankshaft revolution frequency (n) when operating on Diesel fuel and pure rapeseed oil.
As it follows from the analysis of data, application for engine fuelling of crude RO does
not lead to significant changes in general view of the brake specific fuel consumption map.
Typical area of the minimum bsfc values when fuelling the engine with rapeseed oil
locates itself between crankshaft’s revolution frequencies 1600–2000 minK1 and loads of
bmepZ0.53–0.70 MPa, i.e. approximately remains at the same region as it has usually
been monitored during engine operation on conventional fuel. The only feature that clearly
distinguishes the engine performance maps for both fuels tested is the difference in the
brake specific fuel consumption. As it would be expected, the minimum bsfc value for the
engine fuelled with Diesel fuel amounts 225 g kWK1 hK1 whereas when operating on less
calorific oil, the bsfc increases up to 250 g kWK1 hK1 or by 11.1%. During engine
performance on RO at the maximum torque and rated power, the bsfc values in mass were
obtained higher by 12.2 and 12.8%, respectively.