In such an engine, pistons (usually at least four) move up and down and are connected to a crank shaft that translates this into rotational motion. As they move up and down, fuel vapor enters the combustion chamber and is ignited by a spark plug. Then the exhaust must be expelled and the cycle repeats. All of this is controlled by mechanical valves, with each cylinder having at least two. The valves are pushed open and closed rapidly by cams that are driven by the engine. Each valve must make a very tight seal and then reopen in a fraction of a second. All of this, the sparks, the cams and the piston strokes must be perfectly timed.
While all this is happening a separate system continuously pumps oil through the cylinders, keeping their walls coated with oil. The pistons have rings which allow this lubrication to happen while maintaining a seal around the piston. In addition to the oil pump, most internal combustion engines require water cooling, with a separate pump circulating water around the engine and through a radiator.
If that is not complex enough, the torque curve of an internal combustion engine is far less than ideal. Too much load on the engine will make it stall. Too little will mean the engine is not operating efficiently and only slow speeds will be obtainable, despite there being enough power for much higher speeds. Thus, for the engine to operate efficiently, provide good acceleration and for the vehicle to run in reverse, a complex mechanical transmission with multiple gear ratios and a reverse gear is required.
Given the mechanical complexity and the need for such precise timing, it’s amazing these engines operate as well as they do and are as reliable as they are.
A better way?
On its face, a gas turbine seems to be a better solution to the problem of generating rotational motion from the burning of fuel. It natively produces smooth rotational power, with no need for a crank shaft. There are no cams or valves. Although gas turbines require lubrication, the system is simpler. The torque curve is far more favorable. A turbine will not stall in the same way a conventional engine will. If torque load is reduced, it will spin faster, exactly as you would want it to. The transmission is therefore much simpler. It may not even require separate speeds and is only vital as a way of providing reverse capabilities. Gas turbines also are self-cooling, using only the air that flows through them to maintain temperatures.
There are some other, perhaps less important, advantages of a gas turbine. The hot exhaust gas can be used to provide vehicle heat that is nearly instantaneous, with no need to wait for the engine to warm up. The same gas turbine can burn a variety of fuels. So a vehicle powered by a turbine engine could run on diesel, kerosene, gasoline, alcohol or perfume. This is one reason gas turbines are used on the M1 Abrams tank, simplifying the logistics of providing fuel.
It seems logical that an engine that is so mechanically simple, with far fewer moving parts and a near perfect torque curve would be the next big thing in automotive propulsion.
And many tried…
The big three US automakers all spent considerable amounts of money to try to adapt the gas turbine to automotive use, each building a number of prototypes of varying success. GM built a number of futuristic concept cars in the 1950‘s that featured a gas turbine engine.
But no automaker put nearly as much time, money or effort into the gas turbine car as did Chrysler. From the 1950′s until the 1970′s, Chrysler spent millions on programs to deploy gas turbines in cars. They built numerous prototypes, including some which were placed in the hands of various test motorists, who drove them for over a year. Overall, the response from test groups was positive, but there were a number of issues that were never really solved.
The image bellow is of Chrysler’s CR1, arguably the most successful gas turbine car. Fifty five were built and, in 1963, they were given to a group of lucky motorists to evaluate over a year of driving. Although reviews were generally good, the project did not go anywhere. After taking back the cars, Chrysler ended up destroying all but nine of them. Today they are in museums or in Jay Leno’s garage.