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Now that we have learnt about engine classification let's now try and understand Engine Timing and associated Terminology.
What is meant by Engine Timing?
Engine timing is the determination of what happens when inside an engine cylinder i.e at what position and at what instance we have Induction, Compression, Ignition and Exhaust. If all these strokes don't happen at the prescribed/designed time and instance than the engine will not work as it should.
Lets take a simple example.
If we are not experiencing ignition of fuel at a position of piston where it normally occurs than we are likely to experience unfavorable combustion and poor engine performance. As a result it becomes very important for us to understand as to what is happening when inside an engine cylinder so that we can troubleshoot accordingly.
So what all timing cycles are we looking at?
Universally all the engines have 5 cycles i.e. INDUCTION, COMPRESSION, IGNITION, EXPANSION and EXHAUST . Let it be 4 stroke engine or 2 stroke engine, both of hem have to undergo these 5 cycles.
So what's the meaning of these 4 cycles?
INDUCTION - The induction system provides the engine with an adequate supply of clean air for good combustion (and for scavenging cylinders on two and four stroke-cycle engines) for all operating speeds, loads, and operating conditions.
COMPONENTS WHICH ARE LIKELY TO BE FITTED IN AN INDUCTION SYSTEM
- On a naturally aspirated four-stroke-cycle engine, the system includes the air cleaner, a precleaner (if used), the intake manifold, and the connecting tubing and pipes
- On the two-stroke cycle engine, the system also includes a blower for scavenging air and for combustion. A four stroke engine may also have a blower.
- On a turbocharged engine, additional air is supplied by means of a turbocharger, which is exhaust gas–driven.
- On a supercharged engine a mechanically driven blower is used to supply additional air. An air shutdown valve may be included to allow engine intake air to be shut off completely for emergency engine shutdown.
- An intercooler or after cooler may also be included in the induction system. Since cooler air is more dense, a greater amount of air is in fact supplied if the air is cooled.
- The intercooler is mounted to cool the intake air after it leaves the discharge side of the turbocharger and before it enters the engine (before it enters the blower on two-stroke-cycle diesels).
- The after cooler is mounted in the two stroke- cycle diesel engine block so that it will cool intake air before it enters the cylinder ports. Air-to air aftercoolers are mounted in front of the radiator.
At this point it becomes important for us to understand the meaning of these 5 terms:
- INTER COOLER - Is an air cooling device which is placed between the Engine turbocharger or Supercharger and the engines air intake manifold.
- AFTER COOLER - Is an air cooling device which is placed between the LAST Engine turbocharger or Supercharger in series and engines air intake manifold. After Cooler is the last cooling stage before the engine. We can only say that intercooler is connected between the turbochargers/superchargers in series and the last intercooler which is connected to the engines manifold is called the After Cooler. Therefore Intercooler is After cooler.
- RADIATOR - Radiators are heat exchangers which can be used for heating as well as cooling. Radiators are mainly used in cars and are used for cooling the water which circulates around the engine.
- SUPERCHARGERS - Supercharger is typically driven by a belt or a gear powered by the engine. superchargers are good because the horsepower boost is available immediately however supercharger takes the power away from the engine.
- TURBOCHARGERS - The turbocharger creates pressure using the already-burnt exhaust gas that is coming out of the engine to turn the blades of a fan that forces the air into the engine. Turbocharger takes a moment to "spool up" from the exhaust gas. Turbocharger does not take power away from the engine.