The modern combustion engine is a technological marvel, a mechanical miracle that requires little knowledge of its workings in order to use. Unless you’re a car geek, you probably don’t think all that much about your car’s engine.
Until something goes wrong under the hood, of course. When things go bad, the issues and causes can befuddle many drivers, for whom terms like “piston” and “crankcase” are obscure nomenclature, and “boxer” brings to mind Muhammed Ali, not Ferdinand Porsche.
So in order to provide a little clarity about what’s going on under the hood, we at Gear Patrol have pulled together a quick primer on how a combustion engine works and a rundown of the various types of combustion engines available in mainstream consumer automobiles.
Terms to Know
Carburetor: A device that mixes air and fuel in the proper ratio for combustion. The system is mechanical, not electronic like modern fuel injection or direct injection engines; as such, it’s less efficient.
Crankcase: Part of the engine block that houses the crankshaft. Usually made from a one or two pieces of aluminum or cast iron.
Crankshaft: The engine component connected to the pistons that provides rotational motion when combustion occurs.
Cylinder: The portion of the engine block that houses the piston and connecting rod, and the location where combustion occurs.
Direct Injection: A method by which gasoline is pressurized and injected into the cylinder’s combustion chamber. Unlike fuel injection, where gas is injected into the cylinder’s intake port.
Harmonic Balancer: Also known as a dampener, a circular device made of rubber and metal attached to the front of the crankshaft to absorb vibrations and reduce crankshaft wear. It reduces engine harmonics that occur when multiple cylinders move along the crankshaft.
Piston: A component housed within the cylinder walls and secured by piston rings. It moves up and down during the four-stroke combustion process, providing force when exploding fuel and air moves it.
Rev Matching: Technology in manual transmission cars that utilize sensors on the clutch pedal, gear shift, and transmission, sending signals to the electronic control unit that tell it to rev the engine automatically if revolutions per minute fall too low. Rev matching also occurs during the downshift, bringing rpms higher to match the lower gear. This reduces wear on the engine and smooths the shifting process.
Torsional Vibration: Vibration that occurs due to rotating shafts within a car.
The Combustion Engine
Once you get past the protective plastic engine cover found on most new cars, the vehicle’s heart is laid bare: an engine surrounded by a radiator, fluid reservoirs, airbox, and battery. Regardless of how complicated engines can be—thanks in part to features like direct injection, rev matching, etc.—most vehicles make use of what’s known as a four-stroke combustion cycle to convert fuel into kinetic energy. In a nutshell, your engine 1. draws air and fuel in, 2. compresses it, 3. ignites it, pushing the pistons down and generating the mechanical force that moves the car, and 4. expels the air to make room for the next round of the cycle.
Though the actual process is significantly more complicated, the four stages can basically be summed up as such:
