• Investment World
• eWorld
• Catalyst
• Mentor
• Life
• Canvas
• Praxis
• Urban Pulse
• Brand Quest

B. S. Murthy

EVs, fuel cell and hybrid vehicles may be the buzz in the auto industry but there is no getting away from conventional gasoline and diesel technologies. The focus now, therefore is to combine the best features of the two systems to develop an engine that is cleaner, more energy-efficient and has omnivorous fuel consumption capability.

NOW with electric vehicles, hybrids, fuel cells and rotating combustion engines (Mazda RX 8 already in the market) on the way, many among the well-informed public may feel that the days of the conventional gasoline/diesel reciprocating engines are numbered.

Panelists of the Society for Automotive Engineering (SAE 2003 World Congress), however, hold a different opinion on IC engine technology. The existing engine technology, which has had no competitors for nearly a century, has now come to face a challenge as there is a lot of room for improving the fuel economy and reducing emissions by the use of improved combustion systems and electronic technology.

The market force is for cost-effective prime movers, for vehicles that can use the existing infrastructure for maintenance, operation and fuel supply requirements. There seems to be no alternative to these requirements excepting the conventional gasoline and diesel technologies, where research efforts have now to be doubled to fulfil the requirements of fuel economy and reduced emissions.

This article, which deals with "the shape of things to come" for gasoline and diesel technologies, is a companion to the one on diesel technology that appeared last month (Business Line, June 16).

The inherent advantage of higher energy efficiency (and, hence, fuel economy), thermodynamically related with a higher compression ratio, is absent in the gasoline engines at all speeds and loads of vehicle. The fuel economy of the gasoline engine is further affected at the part load by the methods of speed and load regulation.

Mixture-controlled regulation by the throttle valve in the gasoline engine does not substantially change the air-fuel ratio in the mixture, thus the advantage of leaning the fuel in the mixture is denied to the gasoline engine. Moreover, the constant fuel-air ratio makes the exhaust temperature of the engine uniformly high, requiring a heavier cooling system.

Consequently, the gasoline engine would benefit by borrowing the features of high compression ratio and the method of load regulation from its diesel counterpart.

This is the origin of the stratified charge concept, which is a gasoline engine designed with a higher compression ratio, using heterogeneous regions of rich mixtures around the spark plug and progressively leaning the mixture in regions remote from the sparkplug in response to load and speed changes.

Whether the diesel and gasoline engine technologies will merge, giving place to a new generation of engine is early to predict, but the stratified charge engine is illustrative of the convergence of this trend towards producing high performance and low emission gasoline engines.

Gasoline injection (multi-point or single point) is another step towards convergence of the two technologies since you are lending injection benefits of the diesel technology to a carburetted engine, although it is manifold injection.

In the direct injection stratified charge (DISC), or gasoline direct injection engines (GDI), the injection is into the cylinder with a broad range for injection timing, starting from the beginning of the intake stroke (unlike the timing of the diesel engine just before the compression stroke) to match the performance and low emission requirements. But the sparkplug is the ignition source, not the heat of high compression ratio.

Other refinements to approach diesel performance is to use variable valve timing with electronic control (VTEC) using double overhead camshafts, actuating four valves per cylinder and exclusively two cams for each valve for low and high speed ranges. Alternatively, the principle of using eccentric sleeves has been developed by the Motive Engineering Company in the US to vary the point of contact between roller follower and cam to achieve continuous valve timing.

To improve the overall performance of the engine, GM is working on the concept of cylinder-displacement on demand where some cylinders are deactivated by closing of both the valves in response to the load changes on the engine.

Only one strong feature that the designer has failed to borrow from diesel technology is full use of the high compression ratio. Very high compression ratio or supercharging of a gasoline engine increases the tendency to knock, whereas the reverse is the case in a diesel engine. This is a big handicap in the petrol engine which can now be overcome by the use of continuous variable compression ratio (VCR) technology.

FEV Engine Technology, Inc., is engaged in this advanced technology and hopes that it can get close to the fuel efficiency of a diesel engine by this development. This concept is based on the eccentric crankshaft bearing.

The rotation of the eccentric by a 36-volt electric motor, in either direction, permits the centre line of the crankshaft with the piston assembly, to move up or down relative to the cylinder head, thus altering the compression ratio.

This is achieved by electronic control, getting feedback from appropriate sensors in the cylinder, which detects the highest useful compression ratio consistent with the continually varying load and speed dictated by the driving cycle.

The gasoline engine and the diesel engines have their individual advantages. The diesel engine provides fuel economy and performance in all driving conditions.

Further, turbo-charging is attractive to diesel technology, and with good design of variable-geometry turbo charging with electronic control, yields higher power weight ratio and added fuel economy with reduced emissions.

The gasoline engine, on the other hand, with its wide range of power and torque and lower maintenance, is cost-effective.

There is a vision among specialists that the cross-fertilisation of the strong points of these technologies will result in a new generation of clean and energy-efficient engines with omnivorous fuel consumption capabilities. The former chief of Volkswagen, Mr Ulrich Eichhorn, called this fusion of technologies "Combined Combustion System (CCS)."

(The author is a former Professor of Mechanical Engineering, IIT Madras)

Article E-Mail :: Comment :: Syndication

Stories in this Section
Secures little

Copyright © 2003, The Hindu Business Line. Republication or redissemination of the contents of this screen are expressly prohibited without the written consent of The Hindu Business Line