Modern automotive diesels

THE DIESEL engine was invented at the end of the nineteenth century, nearly a decade after the first petrol engined cars appeared on the roads of Europe. That invention has been variously attributed to the Englishman, Ackroyd-Stuart, and the German, Rudolph Diesel. Modern diesels owe their basic design to slightly different features first put forth by both those gentlemen in their initial descriptions of compression ignition engines, the "correct" technical name for diesel engines. Their inventions were ultimately based on fundamental work by the Frenchmen, Sadi Carnot on thermodynamics and Beau de Rochas on internal combustion engines.

Diesel engines were first introduced for stationary power followed by marine propulsion and railway traction applications. It is said that the pacifist Diesel committed suicide during the First World War when he heard of the carnage caused by ``his" diesel-powered submarines. Automobile application in road going commercial vehicles began in the early 1920's while use in large, and expensive, cars only started in the mid-1930s with diesel taxis quickly becoming a fixture in Europe.

Principal advantage

The diesel engine's low fuel consumption has been its principal advantage from the beginning, but not its noisiness, vibration, high levels of particulate emissions and poor power to weight ratio. The latter is because of the very high pressures encountered in the combustion chamber resulting in the need to make all parts of the engine strong and heavy, enough to resist the consequent stresses. A happy result of this "overdesign" is enhanced durability.

This column carried an introductory article on modern diesel cars in February that described some important developments in diesel engine technology since the mid-1970s. In summary, the revolution began with the innovative 1.5 litre, indirect injection (IDI) diesel engine of the Volkswagen Golf (Rabbit in America) and has continued with turbocharging, intercooling, exhaust gas recirculation, electronic injection control, diesel oxidation catalysts and multivalve cylinder heads.

The Golf engine was also noteworthy because it had a belt driven, distributor type fuel injection pump and because it was designed to be made on the same manufacturing line on which the petrol engine on which it was based was made. This latter point is interesting because Honda, the last ``holdout" against diesels, has just taken the same tack - initial introduction of an Isuzu 1.7 litre, diesel engined Civic followed by a two litre diesel engine, for the Accord, to be manufactured alongside petrol engines.

Entry of direct injection

A major change took place in the 1990s with the introduction of direct injection (DI) technology in small diesels, a revolution that is already almost complete with its virtual takeover of the diesel market and strong inroads into the petrol vehicle market. This is remarkable considering that as late as 1994, in spite of its much lower fuel consumption (up to 20 per cent less compared to the already miserly IDI engines) and higher specific output, even the head of diesel engine development at BMW did not think that DI engine technology had much of a future because it was not expected to meet forthcoming emission standards. Central to this paradigm change is new fuel injection technology - ranging from much higher injection pressures and electronic controls to unit pumps and injectors and the so-called common rail (accumulator) systems.

Electronic control whether applied to in-line, distributor, unit injector or common rail systems gives the ability to control the fuel injection process much more precisely than mechanical systems. This applies equally to the injected quantity and timing of the beginning of injection leading to lower fuel consumption, higher power and, not least, lower toxic emissions and noise. Microprocessor based electronic control also allows the introduction of on-board diagnostics (OBD) to monitor the health of the vehicle and to download that information for convenient maintenance and repair. OBD will soon become a mandatory part of emission legislation for diesel engines.

Electronic controls

For example, the VP 37 electronically controlled, distributor type fuel pumps from MICO, a subsidiary of Bosch, should give Indian commercial vehicle and car manufacturers the ability to easily meet Euro III emission standards using the low sulphur (0.05 per cent), 51 cetane number diesel fuel that is beginning to be available. That, of course, is contingent on operators using clean (unadulterated) fuel, maintaining their vehicles properly and, not least, not overloading them!

Most users are unconcerned with these "technical" issues, but what all users find noticeable with the new engines is the improvement in drivability, which includes improved responsiveness, flexibility under varying loads and speeds, increased range of engine speeds and the like. In short, they feel ``in control" without losing any of the traditional diesel virtues like fuel economy and durability. A not inconsiderable bonus is reduced noise and vibration.

A historical retrospective (from the Diesel Engine Handbook) is illuminating with regard to this ``new" technology: ``A fuel system based on the common rail principle was originally introduced by Vickers in 1913 (that is no misprint!) for the Atlas Imperial Diesel Company. This system employed a multi- cylinder pump and an accumulator operating at an approximate pressure of 350 bar with mechanically controlled injector nozzles. It is interesting to note that electronically controlled injector nozzles were also introduced by the Atlas Imperial Diesel Company. The Vickers common rail system with its accumulator as part of the fuel manifold was an attempt to increase the injection pressure by the expansion of the compressed fuel in the accumulator volume."

This ought to be sobering from the point of view of some Indian vehicle manufacturers who see common rail technology as a kind of magical add-on to transform their current engines to ones meeting Euro 3 or 4 standards virtually overnight. It took eighty years, no less, for common rail technology to become technically reliable and commercially viable and at least sixty years even if we count from the time of the pioneering electronic injection trials. Interestingly an Atlas engineer drove its experimental common rail diesel truck all the way from Los Angeles to New York and back (about 14,000 kilometres) braving the primitive roads of the 1930s. The highly innovative Atlas Company sadly went bankrupt in 1945 - the result of a step too far too soon.

The world's leading engine manufacturers are employing hundreds of experienced engineers and spending thousands of billions of dollars struggling to develop Euro 4 compliant commercial diesel engines by 2005 - and they started at least two years ago. It is not a "simple" matter of fitting a particulate trap to an ultra low sulphur (ULSD) fuelled engine!!

On a very different note, the final testing and certification process for diesel aircraft engines meant for light aircraft has begun in France. It is interesting that this engine, from a Renault subsidiary, is taking up from where Russian (or more precisely Soviet) and German practice left off in the 1940s. At the time the miserliness of diesels was seen as their principal advantage in long-range transports and bombers.

Safety first

Visiting Kolkata (it will always remain Calcutta to me) late last March was a pleasant surprise when I saw hundreds of motorcycle and scooter riders, and their pillion companions, all wearing riding helmets. That too on a warm and muggy day.

It is a pity that in Tamil Nadu, the neurosurgeon, Dr. B. Ramamurthi's efforts proved in vain in this regard. One hopes that supposedly anarchic West Bengal can lead India towards safe riding practices.

C. Manmohan Reddy

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