This is an animated computer drawing of one cylinder of the Wright brothers’ 1903 aircraft engine. This engine powered the first, heavier than air, self-propelled, maneuverable, piloted aircraft; the Wright 1903 Flyer. The engine consisted of fourcylinders like the one shown above, with each piston connected to a common crankshaft. The crankshaft was connected to two counter-rotating propellers which produced the thrust necessary to overcome the drag of the aircraft.
The brothers’ design is very simple by today’s standards, so it is a good engine for students to study to learn the fundamentals of engine operation. This type of internal combustion engine is called a four-stroke engine because there are four movements, or strokes, of the piston before the entire engine firing sequence is repeated. The four strokes are described below with some still figures. In the animation and in all the figures, we have colored the fuel/air intake systemred, the electrical system green, and the exhaust system blue. We also represent the fuel/air mixture and the exhaust gases by small colored balls to show how these gases move through the engine. Since we will be referring to the movement of various engine parts, here is a figure showing the names of the parts:
The engine cycle begins with the intake stroke as the piston is pulled towards the crankshaft (to the left in the figure).
Historical note – The opening and closing of the intake valve of the Wright 1903 engine was termed “automatic” by the brothers. It relies on the slightly lower pressure within in the cylinder during the intake stroke to overcome the strength of the spring holding the valve shut. Modern internal combustion engines do not work this way, but use cams and rocker arms like the brothers’ exhaust system. Cams and rocker arms provide better control and timing of the opening and closing of the valves.
With both valves closed, the combination of the cylinder and combustion chamber form a completely closed vessel containing the fuel/air mixture. As the piston is pushed to the right, the volume is reduced and the fuel/air mixture is compressed during the compression stroke.
At the beginning of the power stroke, the electrical contact is opened. The sudden opening of the contact produces a spark in the combustion chamber which ignites the fuel/air mixture. Rapid combustion of the fuel releases heat and produces exhaust gases in the combustion chamber.
During the power stroke, the volume occupied by the gases is increased because of the piston motion and no heat is transferred to the fuel/air mixture. As the volume is increased because of the piston’s motion, the pressure and temperature of the gas are decreased. We have colored the exhaust “molecules” yellow to denote a moderate amount of pressure at the end of the power stroke.
At the end of the power stroke, the piston is located at the far left. Heat that is left over from the power stroke is nowtransferred to the water in the water jacket until the pressure approaches atmospheric pressure. The exhaust valve is then opened by the cam pushing on the rocker arm to begin the exhaust stroke.
Historical note – The exhaust system used by the Wright brothers caused the hot exhaust to exit each cylinder independently … right next to the pilot. This engine was very loud as well. Modern automobiles collect the exhaust from all of the cylinders into an exhaust manifold (just like the intake manifold used by the brothers). The exhaust manifold passes the exhaust to the catalytic converter to remove dangerous gases, and then through the muffler to keep it quiet, and finally out the exhaust pipe.
You should now be able to make some sense from the animation at the top of this page. Notice that the crankshaft makes two revolutions for every one revolution of the cams. This motion is controlled by the timing chain. Also notice how the cam moves the exhaust valve at just the right time and how quickly the intake valve opens after the exhaust valve is closed. In real engine operation, the exhaust stroke can not push all of the exhaust out of the cylinder, so a real engine doesn’t perform as well as the ideal engine described on this page. As the engine runs and heats up, the performance changes. Modern automobile engines adjust the fuel/air ratio with computer controlled fuel injectors to maintain high performance. The brothers just had to watch the horsepower of their engine drop from about 16 horsepower when the engine was first started to about 12 horsepower when it was running hot.