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Physics Behind Modern 4 Stroke Engines Essay

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We've all seen them before, the mysterious chunks of metal under the hoods of our cars. They start when we turn the key and take us where we want to go. But how does an engine work? Internal combustion engines are a very important part of everyday life. We use them in our cars, trucks, airplanes. boats, snowmachines, 4 wheelers, and heavy machinery. These pages will help familiarize you with the basic concepts of how an engine works, an understanding of engine output, and some information on how forced induction or "boost" increases power output.

Engine Basics

A very common variant of the internal combustion engine is the four stroke engine. These engines have four "strokes" for each combustion cycle. These engines are …show more content…

The chemical equation is as follows.

2 C8H18 (gas) + 25 O2 = 16 CO2 + 18H2O

This equation is representative of a stoichiometric air fuel ratio (14.7:1). However under normal driving conditions an engine will encounter lean conditions when cruising on the highway (better milage) and rich conditions when accelerating (better power). The lean condition results in oxide and harmful nitrogen compound production. Rich conditions result in carbon monoxide production. For this reason a catalytic converter is used on most larger engines.

The catalyst material in a cat is in a wire mesh or honeycomb. This allows a high surface area to be exposed to the passing exhaust gasses. The catalyst (typically platinum) converts the harmfull nitrogen oxides and carbon monoxide into nitrogen, carbon dioxide, and oxygen. Catalytic converters work best when warm (as the reaction rate increases with temperature) so some car manufacturers are putting "pre cats" in the exhaust manifold to convert the gasses while the exhaust system is still warming up.

That covers the basic function of an engine fron intake to exhaust. Next we will explore the relationship of Horsepower vs Torque.

Engine output is measured in two ways. The first is a direct measurement of engine output: Torque. Torque is defined as the amount of mass that can be lifted a certain distance from the center of

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