Midnight Oil

Dieselmania in India is not to be wondered at the fuel is cheap, and will remain cheap even after the imminent price revision. But what impels Europeans to buy diesel-powered cars, given that both fossil fuels cost the same there? Performance, fuel efficiency and eco-friendliness might be some of the answers. Read on for more on the wonder fuel that the world calls oil-burners.

The thought of the sticky dark liquid unfailingly conjures up images of smoke, smog and other assorted means of environment murder. Then theres noise, vibration and harshness the NVH factors that engineers try so hard to eliminate in petrol cars, but comes free with diesel engined ones. Then there is the perception that diesel engines, even though economical, are complicated to maintain and expensive to repair.

Most of this negative imagery stems from the fact that we are uncomfortably familiar with diesel motors sporting designs that date back to World War II days. While our experience with these engines has been more noise and visual pollution, few realise that these are in truth less polluting with regard to toxic emissions such as carbon monoxide even though the particulate emission is understood to be carcinogenic. Most will undoubtedly smirk contemptuously on their way to buying another petrol car at the suggestion that most diesel engines are 30 per cent more fuel efficient than their gasoline brethren! The simple fact that all diesel engines possess a fuel injection system and are therefore bound to waste less fuel is not a thought that suggests itself to those droves of petro heads.

Yes, diesel is a greener fuel than petrol. And the point I am trying to make is that the new generation diesel engines are now challenging the traditional virtues of petrol-powered units such as performance without hurting planet earth. Enter direct injection diesel engines.

The internal combustion diesel engine has no spark plugs and uses a method of squirting fuel into the combustion chamber, compressing it to the point of ignition. All major developments in the field of diesel engines have centred around this critical area where the fuel flow from the tank to the combustion chamber takes place. Using a turbocharger to increase the volumetric efficiency of the engine, and an attempt at direct injection of diesel, are the most notable examples of technology revolutionising the way diesel engines perform.

There is really nothing new about direct fuel injection. After all, Rudolf Diesels original demonstrator engine operated on this principle, although obviously with completely different technology. But to develop turbo-charged diesel engines for cars as comfortable and as sophisticated as todays, another technique called the Pre-chamber (or indirect injection of fuel) was invented. This method involves injecting the diesel oil not directly into the cylinder, but instead into a cavity or a pre-chamber arranged so as to contain very strong turbulence. This permits better mixing of the fuel before combustion, and better control over the acoustics of the combustion process itself.

However, direct fuel injection offers an undeniable advantage that of improved fuel economy precisely because of the absence of a pre-chamber. In effect, the direct injection of fuel into the cylinder does away with the continuous energy-draining gas flow into and out of the pre-chamber.

While Mercedes Benz pioneered the diesel engine technology with passenger cars, Volkswagen and their legendary Golf Diesel can take the credit for truly popularising the concept. Renault was one of the first to work towards the goal of direct injection as early as 1982, as part of the Eve Plus prototype programme. This programme clearly demonstrated the potential of the technology for research on low fuel consumption, but also shed light on the considerable challenges that remained regarding exhaust emissions and noise levels.

Major advances followed Eve Plus. The first came with the adoption of this technology in the Renault Master, which in 1989 was equipped with a 2500CC direct injection turbo diesel engine that was good for 88 bhp, later increased to 96 bhp with an electronic fuel injection pump.

Tech talk

So what makes major European auto magazines compare top of the line performance cars with direct injection diesel rivals from Volkswagen, Renault etc? First comes the cylinder head that is completely new, with work carried out in particular on the inlet ports in order to create an aerodynamic swirl within the cylinders to improve gas distribution. The single overhead camshaft operates directly on the valves with no intervening mechanism, thus reducing friction losses. Fuel is supplied by a Bosch high pressure rotary pump with completely electronic control of injection timing and quantity.

The injectors are a twin-step five hole type for better atomisation of fuel particles. The combustion chamber is notable for taking the form of a bowl in the piston crown. Also, the wedge-topped connecting rods bring a better response to mechanical constraints.

The complete supercharging installation is united with a low-inertia turbo unit operating from the lowest speeds. Its efficiency is increased with an air-to-air intercooler.

The F9Qt engine used by Renault in the Megane Diesel is a classic example. Internal aerodynamics is made possible by creating a swirling airflow pattern within the cylinder while the piston descends on the intake stroke. This air movement then continues during the compression stroke and the atomisation of the fuel within the combustion chamber.

Cost of technology

All the properties mentioned above must be maintained during manufacturing, since variations can materially alter characteristics. And the technology has proved simpler than the traditional route of constructing diesel engines. Add the fact that the built in technology leaves very little to be done by way of engine maintenance and you get the picture.

Controlled fuel injection improves the atomisation of fuel, reduces the level of toxic emissions, carcinogenic particulate emission and smoke, increases fuel efficiency, eliminates tradition diesel clatter (less moving parts and thus less friction). And all this without costing the earth, in more ways than one!

The Megane dTi a first drive

The pretty little four-door hatchback in the picture is the Megane dTi. This is the first ever mass-produced passenger car from Renaults stable to sport the direct injection diesel tech. This hatchback is a very well-built car and the monocoque can handle a wide range of engines, ranging from innocuous 1300CC units to 16 valve screechers. And it should come as no surprise that the diesel powerplant is equally acceptable in the engine bay. The tiny four cylinder unit displaces only 1870CC and has the traditional two valves per cylinder configuration. But output figures are beyond the constraints of such a traditional engine lay out the Megane F9QT engine produces 100 bhp at an ultra low 4000 revolutions and there is enough torque to pull a road-roller 200 Nm at 2000 rpm. That translates into a diesel motor with better torque characteristics and low speed agility than most petrol engines and that, at comparable performance.

The Megane can accelerate to 100 kph in 12.3 km flat, 400m standing start run in 18.3 seconds and a complete kilometre standing start in just about 33 nano-seconds. In motorways and autobahns, diesels of the Megane variety can keep up with the best sports cars, what with maximum achievable speeds of 183 kph. However, the most amazing factor is that the Megane can stretch five litres of diesel to 100 kph, that is 20 kpl...(Controlled conditions and steady driving in overdrive produced comparable figures for our very own Peugeot 309 GLD which is powered by a traditional diesel motor. But the GLD produces only 57 bhp as opposed to the 100bhp we are talking of here and acceleration timing was many seconds off.)

The moral diesel is here to stay, and stretch the life of internal combustion engines way into the next century. All that research and prototypes that use dual-power (electric motors mated with small and efficient diesels) are sure to enhance the chances of the diesel engine. Sorry, oil burners.