Design and Simulation of Two Stroke Engines

Chapter 7
Reduction of Fuel Consumption
and Exhaust Emissions
7.0 Introduction
Throughout the evolution of the internal-combustion engine, there have been phases of
concentration on particular aspects of the development process. In the first major era, from
the beginning of the 20th Century until the 1950s, attention was focused on the production of
ever greater specific power output from the engines, be they two- or four-stroke cycle power
units. To accomplish this, better quality fuels with superior octane ratings were prepared by
the oil companies so that engines could run at higher compression ratios without risk of
detonation. Further enhancements were made to die fund of knowledge on materials for engine
components, ranging from aluminum alloys for pistons to steels for needle roller bearings,
so that high piston speeds could be sustained for longer periods of engine life. This book
thus far has concentrated on the vast expansion of the knowledge base on gas dynamics,
thermodynamics and fluid mechanics which has permitted the design of engines to take advantage
of the improvements in materials and tribology. Each of these developments has
proceeded at an equable pace. For example, if a 1980s racing engine had been capable of
being designed in 1920, it would have been a case of self-destruction within ten seconds of
start-up due to the inadequacies of the fuel, lubricant, and materials from which it would have
been assembled at that time. However, should it have lasted for any length of time, at that
period in the 1920s, the world would have cared little that its fuel consumption rate was
excessively high, or that its emission of unburned hydrocarbons or oxides of nitrogen was
potentially harmful to the environment!
The current era is one where design, research and development is increasingly being
focused on the fuel economy and exhaust emissions of the internal-combustion engine. The
reasons for this are many and varied, but all of them are significant and important.
The world has a limited supply of fossil fuel of the traditional kind, i.e., that which emanates
from prehistorical time and is available in the form of crude oil capable of being refined
into the familiar gasoline or petrol, kerosene or paraffin, diesel oil and lubricants. These are
the traditional fuels of the internal-combustion engine and it behooves the designer, and the
industry which employs him or her, to develop more efficient engines to conserve that dwindling
fossil fuel reserve. Apart from ethical considerations, many governments have enacted
legislation setting limits on fuel consumption for various engine applications.
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