Before we go into another discussion about cars, I think we should go back to basics and discuss how certain parts of a car works. Let’s start with the engine.
An engine is basically an air pump. It sucks in air, compresses it and pumps it out. But the main difference is, as air is sucked in, fuel is added, compressed, then a spark is initiated… then we have combustion. Then the burnt gases are forced out and the cycle is repeated again and again. Think of it like a self-sustaining pump.
Now, your basic engine has a carburetor, which controls the amount of air and fuel entering the engine. It mounted on a manifold that directs the air and fuel mixture to the cylinder head (intake port/s). The cylinder-head is the top part of the engine which houses the intake valve/s and exhaust valve/s, valve spring/s, rocker arm/s, camshaft/s and combustion chamber/s. This is where the air and fuel mixture enters the engine through the intake port/s into the combustion chamber and out through the exhaust port/s. The intake and exhaust valves are the ones that allow the mixture to enter and to exit. The camshaft dictates the when and how long the valve stay open or closed. The rocker arm/s relay the movement of the camshaft to the valves. To help remove the burnt mixture, from the exhaust port another manifold, the exhaust manifold, helps direct the burnt gases to the exhaust pipe on the way to the muffler.
Now we go the engine block… inside the block you have cylindrical hole where the piston is housed. This is where the piston moves up and down. Attached to it is a connecting rod—which in turn, is connected to the crankshaft. The gases, when ignited, causes and explosion; which pushed the piston downwards. Each cylinder explodes in a sequential order forcing the pistons to move up and down. The upward/downward motion of the piston converts into the rotating motion of the crankshaft. The front end of the crankshaft is where the pulley is mounted to drive the alternator, air conditioning compressor, water pump and the power steering pump. Behind the pulley is a gear which drives the oil pump and a fuel pump. At the rear end, this is where the flywheel is mounted. The clutch assembly or the torque converter is mounted on the flywheel to transmit rotational motion to the drive train.
Now, where does the spark come from?
For a gasoline engine, you have an ignition coil which steps up the 12 DC volts of the electrical system to around 30,000 DC volts. The electrical current goes through a distributor, which distributes the current to the required cylinder. Each cylinder has a spark plug. This in turn creates a spark inside the combustion chamber. At almost the same time this is happening, air/fuel mixture is being drawn from the carburetor, through the intake valves as the piston goes down. As the piston reaches the bottom, intake valve will start to close. The piston goes up and the air and fuel mixture is being compressed. Note: the amount of air has a certain ration to the amount fuel needed to ignite. By compressing the mixture you also get a stronger combustion. At the exact moment the piston reaches its peak inside the chamber (top dead center), a spark is introduced. Then combustion occurs. The force of the burning mixture forces the piston down and rotates the crankshaft. After it bottoms out, the piston moves up and the exhaust valve opens letting the burnt gasses escape.
In diesel engines, there is no carburetor. No distributor, ignition coil nor spark plug. A mechanical injection pump is the one that delivers the fuel to the cylinders at the proper time. Before starting the engine, a heater plug heats up the cylinder to help with the combustion. It will only stay on for a few seconds. As the piston goes down it draws air into the chamber. Then the piston goes up, the intake valve closes and the air is compressed—about 20 times it’s former volume. In a gasoline engine it is compressed nine times its former volume; 10 for some engines. This makes the air very hot and at the point where the piston is at its highest point. A certain amount of atomized diesel fuel is injected into the chamber. This creates an explosion pushing the piston down turning the crankshaft… as it goes up the exhaust valves open to allow the burn gasses to exit. Both are what can be called four-stroke engines. Because it takes four strokes to complete one power cycle… intake, compression, ignition and exhaust stroke.
Now, for those who may think that I did not cover all the basics of how an engine works… my apologies. We don’t have the luxury of space to discuss things in full detail. But I will try and give more details next time. That’s it for now. Untill next time.
(Dave Siytangco is our resident “car doctor” who will give buying advice and expert solutions for your car troubles. Dave is certified motorhead and runs his very own car repair shop. For questions about your vehicle, please email Doc Dave at firstname.lastname@example.org.)