Oilers Give Full Power on Petrol
Page 48
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AS shown by some graphs prepared by Henry Meadows, Ltd., Wolverhampton, a Meadows 6DC630 oil engine. operating on a commercialgrade petrol with 2 per cent, of lubricating oil, develops approximately the output of. the standard engine of 130 b.h.p. at 1,900 r.p.m. when running on normal fuel. Fuel consumption is virtually unaffected over the maximum-torque range.
It is -emphasized by technicians of the company that
the results so far obtained are the outcome of limited experimental work which is regarded as a preliminary to more extensive development tests. This work was started before the advent of fuel rationing in order to obtain data on the ability of the -engine to use the widest range of fuels.
With minor but important modifications to the injection equipment, it has been proved that an engine can be adapted-to give a similar performance with both types of fuel. Preliminary work carried out suggests that a modified combustion chamber may provide the basis of improved flamepropagation characteristics when burning either type of fuel, but, at the present time, the performances shown on the graphs were obtained with a standard combustion chamber.
Pool Petrol Best
When running with pool petrol of approximately 72 octane, results were relatively good,. but it was found that after mixing the standard fuel with a fuel of 80 octane the results were less favourable.
The importance of eliminating vaporization of the petrol in the injector pump and pipes was fully appreciated before the tests were started. A number of Meadows engines employed for industrial purposes has been performing satisfactorily on paraffin and jet oil for a considerable time, and adaptation of these units to operate on the lighter fuels had shown that vaporization could cause erratic running, loss of H14 power and an increase in exhaust temperatures.
Consequently, the injection pump of the test engine was modified to give a continuous flow of fluid through the gallery, and the pipes were arranged at as great a distance as possible from any heat source to redube the effects of radiation. In bench tests witnessed by The Commercial Motor, the engine ran smoothly over the entire load-speed range and the noise level was normal. There appears to be no smoke limit when burning petrol, and it may be possible, by further development work. to increase the power output.
Injection timing has not yet been adjusted in any way, but the company feel that better results may well be obtained by advancing the timing a few degrees before top dead centre. In order to obtain the power shown on the graphs, it was found necessary to advance the rack setting of the fuel pump to compensate for the lighter fuels.
No . change has been made to the nozzles, which are of the four-hole type, hut development continues in order to obtain optimum nozzle characteristics relative to the combustion chamber employed.
It has been found necessary to bleed the fuel system of air far more regularly than when running on oil fuel, and it is believed that this is caused by the tendency of the fuel to leak past the pump plungers, thus allowing air to enter the fuel lines when the engine is standing. On the other hand, when running, the system is self-sustaining, and at no time has the engine stopped because of air or vapour locks.
Provided that the system is fully primed, the starting characteristics of the engine appear to be unaffected. The Meadows engine is an unusually good starter in its standard form.
A standard C.A.V. " B-type fuelinjection pump is employed, and with a lubricating oil content of 2 per cent., trouble has been experienced as the result of inadequate lubrication of the cams, which were badly scored after 25 hours running. The availability of a pressure-lubricated pump, designed for the use of lighter fuels, would greatly facilitate development work.
The assumption of many operators and a number of engine manufacturers that the use of lighter fuels would lead to dilution of the sump lubricating oil, is not confirmed by the Meadows experiments. Previous tests with the lubricating oils of engines operating on paraffin and jet oil have shown that the additional dilution is negligible, but the company state that further tests are to be carried out to ascertain the specific effects of petrol as a fuel. It is agreed that serious dilution might occur when running on a mixture of 90 per cent. fuel and 10 per cent, lubricating oil.
Paraffin and Jet Fuel
Engines already operating on paraffin and jet fuel develop the rated power and torque over the full load-speed range, and wear rates of both the engine and injection-pump plungers are reported to be normal. The proportion of 10 per cent, was specified by. Meadows in order to provide a wide margin of safety for lubrication of the injection equipment, pending the results of more exacting tests to discover the minimum percentage that could be employed.
Two machines are operating extended tests with 4 per cent, lubricating oil in jet fuel, and it is expected that results from these tests will be available within the next 12 months.
In its industrial form the 6D.T630 engine is rated at 100 b.h.p. at 1.600 r.p.m. for continuous duties.