Further Experience with Creosote
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IN the past few days we have had an opportunity for travelling from London to Oxford and back on a Gifford 1680T-type motor coach belonging to South Midland Motor Services, Ltd., which has been converted by J. M. Horne and Co., Ltd., 170, Hornsey Lane, London, N.6, to burn creosote, a home-produced fuel of high anti-knock characteristics, utilizing the Solex hi-fuel system. The cost of conversion is about 155.
The vehicle has a Coventry-Climax engine of 31-in. b2re and 5-in, stroke, the capacity of the six cylinders being 5.9 litres. The original compression ratio was 4.58 to 1, and this has been raised to 6 to 1. As no detonation at all is detected at normal ignition advance, it appears that the ratio may safely be raised to 6.5 to 1, and the Horne concern has subsequently tried this with good results. For our test run on the vehicle, the fully advanced ignition position was 33 degrees before top dead centre, made earlier still to the extent of two teeth on the Simms coupling. The engine had a Bosch magneto and Lodge CV1 plugs.
In place of the original Zenith 4211 carburetter with 27 choke, 110 main jet and 115 compensating jet, a Solex 40 MOHD horizontal carburetter for the creosote has been mounted just below the special manifold and at present has a 28 choke, 195 x 44 main and 50 pilot jet. Below this is a vertical Solex 26 mm. carburetter with slow-running jet, this being used for idling and starting on petrol.
In the riser pipe, between the petrol and the creosote carburetters, is the Solex governor, this being a gas-tight butterfly inter-connected with the throttle of the creosote carburetter; the control is by the accelerator pedal to a fulcrum arm having optional holes to permit of adjustment of the overlap, that is, the period between the commencement of opening of the creosote throttle and the closing of the Solex governor. As the accelerator is depressed, the creosote carburetter is brought into action, the petrol carburetter being afterwards cut completely out
In place of the separate manifold, a combined manifold has been designed by j. M. Horne and Co., Ltd., which ingeniously applies heat to the creosote spray to vaporize the Melt-boiling-point fractions. The oil at present used is supplied by Low Temperature Carbonization, Ltd., 28, Grosvenor Place, London, S.W.1, and is claimed to differ from hightemperature-carbonization fuels in that the solid naphthalenes, which are inclined to crystallize in cold weather, do not form at the low temperatures used in production.
With the 6.5-to-1 head and the same carburetter setting as above, we learn, a gradient of 1 in 16 was climbed at 14 m.p.h. in second gear, the gross weight being 6 tons 17 cwt., whereas with a similar vehicle running on petrol and loaded to 6 tons 2 cwt. 15 m.p.h. is about the minimum speed. With the 6-to-1 compression the power may have been slightly less than on petrol, but superior power would be expected with the higher compression, judging by other Solex experiments.
The regular drivers agree that there is an improved smoothness of running, due, no doubt, to the different flamepropagation characteristics. They agree also that the lowspeed torque of the engine is somewhat better. There is no flat spot at the change-over from petrol to creosote, for accurate adjustment of this control is easily obtained by means of the fulcrum arm, referred to above.
B24 As regards the all-important subject of smoke, we detected no visible exhaust smoke, except momentarily after each deceleration (for traffic, gear-changing, etc.). On these occasions a puff of smoke was emitted, which was gone in a second or two as the engine pulled away under load. • file cause of this appears to be that the gas shock which occurs when the throttle is suddenly closed throws the oil out of suspension. The experiments of other concerns have shown that the addition of a little air at this juncture usually eliminates the smoke puff, for, although the air is cool, it seems to add enough oxygen to the contents of the manifold to burn the remaining fuel.
The Horne concern is now looking into this suggestion. It needs careful handling, for everything depends upon the spring pressure of the automatic air-inlet valve, which must not lift under idling conditions, as that would stall the engine as well as destroy the depression required for vacuum braking. Of course, this smoke puff can often be cured by using a hotter manifold and, in the present case, it is just possible that that may be what is wanted, although an over-hot manifold would naturally mean loss of power. As regards lubricant, on the vehicle in question Wakefield Castrolote, which contains a large proportion of first-pressure castor oil, is being used. We examined a sample from a warm engine after 300 miles of running • it was a light sepia colour, had a fairly strong creosote odour and a good viscosity. The castor-base oil is perhaps over-viscous when fresh and seems to drop quickly to its proper viscosity and to remain at that.
We were, of course, unable in this test to see whether, after a few hundred miles, there was any excessive carbon deposit under the inlet valves, in the inlet pipe or in the cylindere, but from the cleanness of exhaust under load we should not expect this.
The Gifford vehicle is at present doing two London-Oxford return trips (242 miles) on 28 gallons of creosote and 3* gallons of petrol, and the petrol consumption is rendered heavy by rather too much warming up, etc. We are told that the same vehicle, running on petrol, averages about 30 gallons for the 242 miles. The economy arises out of the cost of the creosote, which is about '7d. a gallon for bulk quantities delivered. The converted vehicle has now covered over 1,000 miles in public service, maintaining its regular time schedules.
The engineers of the Horne company do not claim to have reached finality in their efforts and, in addition to trying a 6.5-to-1 compression ratio, expect improvements in carburetter setting, as well as, perhaps, from an air-inlet valve. Also a lead-away from the crankcase breather would doubtless remove the slight creosote odour from the vehicle interior.
In conclusion, research with this bi-fuel system appears to be proceeding on the right lines; it is difficult to see bow any measure of success is obtainable without petrol for slow-running purposes, because, during idling, there is neither velocity nor heat to keep heavy fuels in suspension. It is an important thing to idle the engine for about five minutes on petrol before switching off each night to prevent it being gummy in the morning.