The Combustion Engine

There is no question to the magnitude of the impact that the internal combustion engine (ICE) has had on our civilization. Their application in industry has fueled our worldwide economy, and personal automobiles have become a near necessity. Since the creation of the first successful internal combustion engine in 1860 by a French designer Jean Joseph Etienne Lenoir, many improvements have been made to the original idea. Today’s engines are far more reliable, generating greater amounts of power and torque, utilizing modern computers in the fuel injection

system, producing less pollution, and due to mass production have become more affordable. Although gasoline engines have improved over the years, they are still not very efficient at converting chemical energy into mechanical energy. The overall efficiency of a typical gasoline internal combustion engine is about 30%. The rest of the combustion energy is converted into heat during the cycle. The efficiency of the cycle is lowered by waste that is dissipated to the cooling system, exhaust, and the atmosphere. The question arises as to “why is all this heat energy wasted?” The answer to this question lies in the materials used to construct the engine, and more importantly, the material properties.

Temperatures in the combustion chamber of the engine can reach a scorching 2200C.  If no cooling system is implemented, the metals within the chamber will get hot enough for the pistons to actually weld themselves to the cylinder. The end result is a complete destruction of the engine. Even though the cooling system drastically reduces the efficiency of the ICE, a conventional internal combustion engine could not survive without it. The depletion of natural resources, and concerns for fuel cost, and pollution promote the need for a more efficient engine. Since most of the energy lost in the engine is due to heat dissipation, decreasing heat dissipation increases efficiency.    The solution is to create an adiabatic engine.

The Adibiatic Goal

An adiabatic system is defined as one in which no heat is supplied or rejected by the system. In reality, no true adiabatic system exists, but the idea is to strive towards the theoretical system by reducing the amounts of heat entering and exiting the engine. To meet this goal, typical ICE engines should be redesigned with better materials.  By reducing the weight of the engine and its components, we reduce the amount of work that must be output by the engine. A common rule of thumb is that a 100-lb reduction of weight in a car is an equivalent to a gain of approximately 10 horsepower. To improve the efficiency of the chemical reaction, which takes place during combustion, we need to increase the percentage of fuel combusted per cycle. The biggest improvement to the performance and efficiency of an internal combustion engine will be creating an adiabatic system. It is common knowledge that a warm engine performs better, and more efficiently than a colder one. A redesigned ICE removes the radiator and cooling system entirely.  Thus, 15% of the heat is in effect being reintroduced to the engine.  Thirty percent of this previously removed radiator heat can be used to produce useful work.

Materials Considerations

The combustion chamber comprises: the cylinder heads, cylinder, piston, and valves. Traditionally, carbon or aluminum alloys are the materials of choice for these components.  High heat and increased friction causes pistons to weld themselves to the cylinder lining. New materials are needed to substitute for the aluminum counterparts. Material properties for these new parts include: high strength, low density, low thermal expansion and thermal conductivity, high thermal shock resistance, and extremely low wear. Alloys such as ones that are used in high temperature turbines can be substituted, however, the same degree of heat treatment is not required.