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Alcohol in diesel engines -- Have technology, will travel -- policy permitting

B. S. Murthy

Petroleum fuels are rough and tough

It's time to say enough is enough.

Surely, your cars can go alcoholic,

Unlike man, they run without panic.

Blue flame special is smokeless and sober,

Speeding away from oil sheikhs forever.

IN SPITE of the proven merits of ethanol as an environmentally safe and high-performance renewable motor fuel for nearly three quarters of a century, it is unfortunate that India has not shown the political will towards wide application of alcohol fuels for motor vehicles. It is only after the recent article by Mr Ram Naik, Union Minister for Petroleum and Natural Gas (Business Line, June 21), that new hope has emerged for a revival of interest in this renewable energy source that could gradually replac e petrol, thus greatly benefiting the economy.

In the mid-1930's, petrol/alcohol blends were used in the city bus service of Bangalore as an experimental measure, owing to the vision of the then Dewan of Mysore, Sir Mirza Ismail. And in Brazil, there was a strong political will to implement alcohol f uels as a national policy and be free from the burden of importing petroleum fuels. Mr Ram Naik's timely article has indicated that India too can gradually implement alcohol fuel technology for automobiles -- first, as a blend in petrol cars, and subsequ ently as a sole fuel for both petrol and diesel vehicles.

Alcohol in diesel engines

Alcohol, especially ethanol or ethyl alcohol, has been recognised as a quality motor fuel, as the design of the first automobile (the original Ford Model-T) for the spark-ignition engine because of its high anti-knock value designated by the `octane Numb er' and better performance in terms of power and efficiency. It is only recently (since the 1970s) that interest was shown in the use of ethanol and methanol as diesel fuels.

Alcohols are very difficult to burn by compression-ignition, because of their low ignition quality, usually designated by a low `cetane number'. A high-octane fuel (a virtue for a petrol engine), necessarily has a low cetane value (a curse for the diesel engine). The main research in diesel-alcohol technology was to find ways and means to force alcohol to ignite by compression in the diesel engine.

It is interesting that India was the earliest to recognise the merits of burning ethanol in diesel engines. The bi-fuel system developed by the Prof H. A. Havemann and his colleagues at the Indian Institute of Science (IISc) Bangalore, in the early 1950s , was the subject of the earliest original published work in technical literature regarding alcohol diesels.

Essentially, this method involves giving carburettor benefits to a diesel engine. Part of the fuel-energy is supplied by inducting ethanol through a carburettor, while only a small quantity of diesel fuel is injected in the conventional injection system. Since alcohol and diesel oil (unlike petrol, which can be blended) do not mix, these fuels are sent through two different routes -- by induction and injection.

Injected fuel, which is a smaller quantity, only serves as an ignition source, like millions of distributed spark plugs. By a proper choice of injected fuel, either diesel oil or vegetable oil, a large portion of ethanol -- 40-90 per cent -- can be utili sed by this method. This pioneering technique did not attract widespread application as the availability of petroleum fuels eased up, and there were no environmental constraints on the use of diesel oil in those days.

Similar approaches were concurrently investigated in the US and UK, but they did not use alcohol. Prof Paul Schweitzer of Penn State University ``fumigated'' the induction system of a diesel engine with different volatile fuels, while injecting conventio nal diesel oil to improve the air utilisation of the diesel engine and boost power.

In an impressive SAE publication on ``Hybrid Engines'', Professor Schweitzer referred to the research efforts at Bangalore on the novel attempts to burn a low-cetane fuel like alcohol by ``fumigating'' it to the induction manifold. Pennsylvania State Rai lway also showed interest in applying this technique for using alcohol in diesel locomotives.

The UK experience, in King's College, was aimed at improving combustion characteristics of a diesel engine by introducing small quantities of `Secondary fuels' in the induction manifold and promote smooth pressure rise and low smoke emission. Though diff erent names were adopted, the Indian, US and UK efforts were all directed at improving diesel combustion and promoting the use of alternative fuels. But only the Indian researchers directed their work towards ethanol for the partial substitution of diese l using this bi-fuel approach.

Ethanol-diesel road trials at IIT Madras

The pioneering experience at the IISc promoted many follow-up investigations at various centres in India -- IITs, universities (especially, the College of Engineering, Guindy) and CSIR research laboratories (such as the Indian Institute of Petroleum, Deh radun). There are significant agreement on the advantages of this method -- about 10-15 per cent boost of power because of better air utilisation and improved charge efficiency arising out of the inflow of cooler charge, increased thermal efficiency and lower smoke density only in certain ranges of load and speed.

More significantly, absolute or anhydrous alcohol was not required for fumigation, in contrast to the blending practice for petrol engines. Anhydrous alcohol is expensive. Rectified spirit as it is could be used for diesel engines. Water, indeed, proved a blessing in disguise as the much-blamed nitric oxide emissions characteristic of diesel engine reduced because of water in the alcohol and the low combustion temperatures caused by high latent heat of alcohol.

Vehicle diesel engines are variable-speed engines and, to reap maximum advantage of fumigation, the ethanol must only be fumigated into the induction system in a controlled way after ascertaining the load and speed at which low smoke; high volumetric and thermal efficiencies were possible. In 1980, researchers at IIT Madras embarked on a collaborative project with the erstwhile Standard Motor Company and Carburettors Ltd on the vehicular application of ethanol in diesel vehicle by fumigation and conduct the road trials.

This alcohol-diesel powered vehicle (Standard 20 microbus) was demonstrated at the exhibition held by at Pragati Maidan, New Delhi. The results are briefly results summarised below. (Details are documented in the Special Publication SP-480 of SAE on alte rnative fuels).

The heart of the technique was a special air-alcohol inductor, designed after extensive tests on a laboratory dynamometer. The novelty of this gadget is that under starting and idling conditions, the throttle of the single jet carburettor is closed and t here is no flow of alcohol and the vehicle works on neat diesel oil. The throttle in the air arm is fully open when the throttle in the carburettor arm is fully closed. They are complementarily ganged. Together, they are linked by a flexible coaxial cabl e to the control lever of the diesel injection system which, in turn, is linked to the accelerator pedal.

The relative sizes of the venturi and the carburettor jet, and its position relative to the venturi, are designed such that the jet does not allow any alcohol till the predetermined speed compatible to efficiency and smoke number (as determined by the st atic dynamometer tests) is reached. At speeds higher than this, there is automatic controlled flow of pre-determined alcohol flow conducive to the fuel efficiency and low smoke number. This technique permits complete working on diesel fuel in case of dis ruption in the supply of alcohol.

Road trials with the retrofitted diesel vehicle indicated that unto 45 per cent of diesel oil substitution was possible under transient conditions of driving on our roads. Bi-fuel systems can be introduced without major changes in the vehicle hardware ex cepting that two tanks are needed. Material compatibility with alcohol fuels has already been solved, just as in the case of petrol engines.

This system, while admirably suited to stationary engines, works on maximum alcohol substitution on diesel locomotives, which run at high speeds and constant load for long distances. Rectified spirit instead of anhydrous alcohol can be used. Fueling for fleet vehicles can be done without major changes in fuel supply and distribution infrastructure.

Alcohol-diesel technology: Recent advances

IIT Madras is credited with research on the use of alcohol as a sole fuel. Ignition of alcohol on catalytically activated surfaces in the combustion chamber has enabled its use as a sole fuel. Many results of collaborative work of IIT Madras and Santa Cl ara University as well as the Technical University at Aachen, Germany have become an important source of reference for research. Detroit diesel engines, working on two-stroke principle, used another novel method for force-igniting methanol by hot exhaust gases held back and trapped by partially closing the gate of the turbocharger (recently, this method was also extended to ignite CNG in the diesel engine).

MAN diesel buses were tried on neat methanol by hot surface ignition -- a method favoured by researchers at IIT, Madras. Prof R. K. Pefley, director of Alcohol Energy System, Inc, invited the Indian team to exchange their experiences with the US efforts. The Indian Institute of Petroleum (IIP), Dehradun, took a leading role in exchange of alcohol fuel technology in several workshops conducted by them in collaboration with IIT Madras and the Santa Clara University.

Making emulsions of ethanol in diesel fuel by the use of surfactants is an accepted practice in Sweden. Ethanol with ignition improvers has now become an established bus fuel. The Swedish company, Sekab, works in these areas and manufactures this fuel, c alled Etamax-D, as a sole fuel. Blends of 85 per cent diesel and 15 per cent ethanol under the proprietary name Etamix-D are also made.

In sum, ethanol fuels and ethanol blends are environmentally clean fuels derived from renewable sources such as sugar-cane, molasses and cellulose from bagasse. India can well start diesel-alcohol programmes on fleet buses, locomotives and stationary eng ines using the skills and potential of the IITs, IIP and the universities. Expertise developed in India is already being used in other parts of the world!

(The author, a retired IIT professor, is a former consultant to Alcohol Fuel Systems, Inc., California.)