Submit an Article

---

Internal Combustion Engines. Article courtesy of http://RacingSecrets.com An internal combustion engine is any engine that operates by burning its fuel inside the engine. In contrast an external combustion engine burns it fuel outside the engine, for example a steam engine. The most common internal combustion engine is the gasoline powered engine. Others include those fueled by diesel, hydrogen, methane, propane, etc. Engines typically can only run on one type of fuel and require adaptations to adjust the air/fuel ratio or mix to use other fuels. In a gasoline engine, a mixture of gasoline and air is sprayed into a cylinder. This is compressed by a piston and at optimal point in the compression stroke, a spark plug creates an electrical spark that ignites the fuel. The combustion of the fuel results in the generation of heat, and the hot gases that are in the cylinder are then at a higher pressure than the fuel-air mixture and so drive the piston back down. These combustion gases are vented and the fuel-air mixture reintroduced to run a second stroke. The outward linear motion of the piston is ordinarily harnessed by a crankshaft to produce circular motion. Valves control the intake of air-fuel mixture and allow exhaust gasses to exit at the appropriate times. The two-stroke type of internal combustion engine is typically used in utility or recreational applications which require relatively small, inexpensive, and mechanically simple motors (chainsaws, jetskis, small motorcycles, etc). The two-stroke engine is simple in construction, but complex dynamics are employed in its operation. There are several features unique to a two-stroke engine. First, there is a reed valve between the air-fuel intake and the crankcase. Air-fuel mixture enters the crankcase and is trapped there by the one-way reed valve. Next, the cylinder has no valves as in a conventional four stroke engine. Intake and exhaust are accomplished by means of ports - special holes cut into the cylinder wall which allow fuel-air mixture to enter from the crankcase, and exhaust to exit the engine. These ports are uncovered when the piston is in the down position. Air-fuel mixture is drawn into the crankcase from the carburetor or fuel injection system through the reed valve. When the piston is forced down, the exhaust port is uncovered first, and hot exhaust gases begin to leave the cylinder. As the piston is now in the down position, the crankcase becomes pressurized, and when the intake port into the cylinder is uncovered, pressurized air-fuel mixture enters the chamber. Both the intake and exhaust ports are open at the same time, which means the timing and air flow dynamics are critical to proper operation. As the piston begins to move up, the ports are closed off, and the air-fuel mixture compresses and is ignited; the hot gases increase in pressure, pushing the piston down with great force and creating work for the engine. The major components of two-stroke engines are tuned so that optimum airflow results. Intake and exhaust tubes are tuned so that resonances in airflow give better flow than a straight tube. The cylinder ports and piston top are shaped so that the intake and exhaust flows do not mix. The four-stroke internal combustion engine is the type most commonly used for automotive and industrial purposes today (cars and trucks, generators, etc). On the first (downward) stroke of the piston, fuel/air is drawn into the cylinder. The following (upward) stroke compresses the fuel-air mixture, which is then ignited - expanding exhaust gases then force the piston downward for the third stroke, and the fourth and final (upward) stroke evacuates the spent exhaust gasses from the cylinder. The four-stroke cycle is more efficient than the two-stroke cycle, but requires considerably more moving parts and manufacturing expertise. The diesel cycle is a type of internal combustion engine in which the burning of the fuel is not triggered by a spark plug but rather by the heat generated in compressing the fuel air mixture. Because diesel engines operate at higher temperatures than four stroke cycle engines, they are more efficient and are therefore preferred for large vehicles such as trucks. Rotary engine is a generic term used to describe an engine that typicaly contains a triangular piston. They are often referred to as Wankel engines after the engine's inventor Felix Wankel. These engines also contain very few moving parts (e.g. no valves), quite the opposite of other internal combustion engines today. Wankel engines tend to be very light weight, quite compact, and very powerful for their small volume. Disadvantages include mediocre fuel economy, difficulty in achieving pollution control, low power at low torque, problemetic low temperature starting, and difficulty in lubricating the rotating seals. The most prominent car manufactured with this engine is the Mazda Rx-7. The term "rotary engine" was also applied to a completely different kind of engine, used especially as engines for aircraft up to about 1920. This was a conventional reciprocating internal combustion engine. The distinguishing feature was the arrangement of the cylinders. Usually there were 7 cylinders, and they were arranged radially about a central crankshaft. See also Radial engine. In the case of a rotary engine, the crankshaft was fixed solidly to the aircraft frame, and the cylinders spun round, attached to the propeller. This was supposed to have two benefits: * With the large rotating mass of the cylinders, there was no need for a flywheel. * With the cylinders spinning rapidly, there was improved air-cooling of the engine. By about 1920 it was obvious that both of these arguments are bogus. * With a large rotating propeller, aircraft engines don't need flywheels anyway. * With the speed that aircraft fly through the air, there is usually plenty of airflow to cool the engine anyway. Rotary engines had some disadvantages too. The need to have 7 cylinders (each in a separate cylinder block) moving at high speed made for extra complexity and weight to hold it all together. This is not good in an aircraft engine. Perhaps more seriously, having such a large weight spinning in an aircraft produces significant gyroscopic effects. Maneuvering an aircraft with this kind of engine required a lot of skill since it didn't always respond to controls as expected. It is said that the Sopwith Camel, powered by a rotary engine required full left rudder to turn left, and full left rudder to turn right, but neutral rudder to fly straight ahead. For all these reasons, rotary engines of this kind became rare as aircraft engines after about 1920. They were never very popular for other uses. Send this article to a friend Submit an Article Sign up for our FREE Racing Tech Newsletter Webmasters: You may freely reprint this article on your website provided the following caption remains intact, along with a working link. This article courtesy of http://RacingSecrets.com , your racing technology resource.