The Engineering behind Automobile Engines – Explained

(Pictured above is the new Inline 6 engine block concept from Mercedes-Benz that is rumored to revive the so called “dead” I-6 in today’s world.)


What exactly are Car engines?

Well by definition an engine is any device that can take in some form of input (force, energy, etc.) and perform some work to produce output energy. And car engines live and breath on that exact principle. More specifically the engine in your daily commuter is called an Internal Combustion engine (IC engine), which means the “work” preformed is a chemical reaction involving heat. And heat is a very ideal form of energy since it means that the molecules have a lot of kinetic energy and hence means that they can produce a LOT of force over a lever arm (piston) to produce usable torque to turn a crankshaft to rotate the wheels for propulsion.

The 4- stroke engine cycle:

At the heart of car engines is a device called a Piston, that moves up and down in a hollow cylinder opened at the the top and bottom. The head of the piston, as shown to the right, is always perfectly lined with the inner wall of the cylinder which leads to a vacuum in there below the head. The “tail” of the piston is connected via links to a universal shaft called the crankshaft, based on its shape. This shaft is connected to all the pistons in the block and helps to convert the linear motion of the cylinders to rotational motion, that in turn is fed to your wheels.



Now the magic happens in the cause of up and down movement of the pistons. Little explosions of air-fuel mixtures occur above the pistons to push them back down and keep the crankshaft rotating. Gasoline mixes well with air and once sparked up, it explodes, releasing a lot of energy.

  1. The first “step” is the INTAKE, where a valve above the pistons opens and allows an air-fuel mixture to come into the cylinder
  2. The second “step” is the COMPRESSION stroke, where the momentum of the piston makes it move up and compress the air-fuel mixture against the ceiling wall. The idea is that as volume decreases, pressure increases and hence if the air is more pressurized, the effect of combustion will be greater.
  3. The third “step” is POWER and includes the explosion, using sensors, a spark plug ignited the mixture and hence forces the piston back down.
  4. The final “step” is EXHAUST, where the products produced by the reaction (CO2, NO2, CO) are sent out through a valve that opens in the top, expelled out the car through the tail pipe.


This process takes place takes hundreds of thousands of times (rpm) and all the rotational momentum is sent out through the flywheel (the big disc connected to the crankshaft) and out to the transmission.

The camshafts at the top of the engine block are shafts that open and close the aforementioned valves, to let in/out air. They are connected with a timing belt with the crankshaft and move at half its speed. The cam has profiled lobes that rotate and accordingly press down on their respective valves when the time comes. Well then through all this, the very big question that arises is that how do you start up a car? Since the whole system is self-dependent? Well the engineers have thought that out as well, with a starter motor that receives a signal from the battery (when you turn the key) uses a small gear and spins up the flywheel (the disc). From here the sensors in the ECU (engine control unit) do their job and get the 4-stroke cycle to life.










Thanks to:

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