Call for diesels to use methanol
Page 60
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Bill Godwin reports on the latest developments on energy saving from Sweden, Germany and Italy.
MILITARY NEEDS for an engine which did not require a specific grade or type of fuel laid the basis for current development work on adapting diesel engines to run on alternative fuels. That is to say, fuels for which they were not designed in the first place.
The main thrust of such work now is of course to reduce the transport sector's dependence on oil. Already Brazil, for example, is using locally produced methanol in car and cv engines and the city of Vienna is using buses powered by lpg.
Other possibilities include various hybrids such as some diesel/electric prototype buses already in use in Germany and the rediscovered energy recuperative flywheel.
Yet there is no sign that any of these marginal techniques is likely to supplant the automotive power unit as we know it for a long,long time. So any development which prolongs the life of the internal combustion engine by modifying it for another fuel is bound to be worthwhile.
So Volvo's announcement that it is to fit diesel engines "doctoredto run on methanol to articulated Stockholm city buses comes at the right time. As part of the Swedish government's policy to safeguard the operation of the transport sector by reducing its requirement for imported fuels, tests have been under way since 1975 with diesel engines modified to run on a methanol /diesel system.
The experimental programme, under the direction of Svensk Metanol-Utveckling AB (Swedish Methanol Development Board), have included vehicle trials in a Volvo N10
truck. Fitted with a TO 100-A six-cylinder in-line turbocharged 10-litre engine with a second, methanol, injection system the vehicle has so far completed over 10 000 -n in .uei Opc. a contractor to the building industry.
In the field trials, methanol has represented 70 per cent of the fuel used. Methanol has a low cetane rating and will not usually ignite by compression. Diesel oil is therefore used as a "sparking plug" to fire the methanol. The greater the load on the engine, the greater the percentage of methanol which can be used.
This is because the diesel oil feed remains almost constant; in fact at low load only diesel is injected. In the underfloormounted installation for the Stockholm bus, the additional fuel system necessary is catered for by the original pump and fuel lines; the diesel oil has been assigned a new system of its own comprising tank, feed pump, injection pump and injector.
Much of the experimental work has centred on optimising the injection of the igniting fuel with special attention to direction, quantity and timing to provide safe ignition under all conditions.
The method devised of injecting the igniting fuel against the air swirl results in very low emission; it also improves ignition for fuels of a lower cetane number or enables lower compression ratios to be applied in high output diesels.
Another confirmation of faith in the diesel engine as the most appropriate power unit in passenger transport use comes from the current Italian research and development programme under which two alternative hybrid bus proposals retain the diesel as the main power source.
The Italian CNR project and associated work by the Fiat Research Centre is now entering its third year and it is expected that a prototype "energy saving" vehicle will be demonstrated by the end of autumn 1979.
Advantages of the engine/electric hybrid design for commercial and passenger vehicle use include, ia, selection of the most appropriate operating mode for the primary energy source itself.
Much of this work has also been expanded by German manufacturers, viz MercedesBenz, Bosch, etc, but it is the second approach chosen by the Italian team that appears to have considerable potential in bus applications where installation weight and size are more easily accommodated than in a van or truck where the payload factor is the ultimate criterion.
The vehicle now nearing completion is based on a front underfloor-engined Fiat 418 AL 11-metre bus chassis with an hydraulic power-splitter transmission in the driveline to the rear axle. An under-chassis, mounted flywheel is connected to this divider and driven through a clutch and reduction gear by the diesel engine.
Final drive to the axle is by one of three modes. all hydro static, mechanical with power return to the flywheel, power split mechanical /flywheelhydrostatic. The various modes are obtained without discontinuity of velocity (or inertia on the hydro transmission and clutches) by electronic control gear. The main benefit to be derived from this system is a reduction of fuel consumption; initial evaluation under laboratory conditions has placed this as 30 per cent.
Flywheel energy also features in the German project briefly described in Commercial Motor, June 29. It differs, however, from the Italian technology in that the flywheel is only charged — by "feedback" from the roadwheels — when braking and that the energy thus recuperated is used again when accelerating. It follows, therefore, that this method is particularly apposite in the city bus installation with its repeated "stop-gocycles.
Both Daimler-Benz and MAN are building prototype vehicles fitted with the device; thE former is devising a hydrostatic splitter for power transmissior in 16-ton-gross city buses a! well as an alternative for smalle psv in which the splitter func tion is provided by an electri( drive.
Daimler-Benz is also inves tigating modified forms of fly wheel drive to provide full trac tion over short stretches c routes in tunnel where thi method would obviate the prc vision of costly ventilation sy: tems. It may be recalled that
"gyrobussystem, in whic flywheels were recharged E
specially fitted terminal point provided years of public servic in the early 1950s in the Swis town of Yverdon.
In the German developmen weight of the total flywheel drive system equals that of bus with automatic transmis sion since the weight of th flywheel (steel or Kevlar fibre) i partially compensated for b the possibility of fitting a sma er, lighter, engine.