Internal Combustion Engine in Aviation
This section we are going to understand the power plant of an aircraft. The power plant by its name tells us it generates power and how does it derive it? The normal aspirated engine and propeller, in training aircrafts and in bigger planes its gas turbine engines. This chapter deals with the normal aspirated or the internal combustion engine. But before we go on how would you define power plant? I would define it, as that essential component of the aircraft that produces thrust.
The internal combustion engine is a reciprocating engine, its called so because it uses the up – down or to and fro motion of the piston, the mechanical motion of the piston is used to accomplish work. I have noticed many times while talking to people, they are extremely confused and have messed up concepts about the internal combustion engine.
The internal combustion engine combusts fuel with an oxidizer in a combustion chamber, which basically means that the fuel is burnt in a combustion chamber. The components of a normal aspirated engine are :
1. Piston : cylindrical in shape and moves up and down to generate mechanical energy.
2. Cylinder : casing around the piston. It is air-tight.
3. Piston Rings : attached to the piston and because of these rings the cylinder remains air tight.
4. Connecting Rod : its a rod that is connected to the piston and the crank shaft.
5. Crankshaft : It converts reciprocating linear into rotation, its connected to the connecting rod. The crankshaft has “crank throws” or “crank pins”, additional bearing surfaces whose axes are offset from that of the crank, to which the “big ends” of the connecting rods from each cylinder attach.
6. Spark Plug : it generates a spark in the cylinder that com-busts the fuel air mixture. Note that in a diesel engine there are no spark plugs.
7. Intake and Exhaust Valves : usually a poppet valve, these valves let the fuel air mixture in (intake valve) or show the exhaust gases the way out of the cylinder.
8. Intake and Exhaust Cam Shaft : is a shaft that a cam is attached to. This basically means that it controls the valve timings for the cylinder. It tells which valve to open and when to close.
These are the basic parts that you would find in a four-stroke cycle. Now, its also important to remember what is dead center. Dead center is the position of the piston in which it is farthest to or nearest to the crankshaft. The former is called Top Dead Center (TDC)and the latter is known as Bottom Dead Center (BDC).
The Four-Stroke cycle refers to four distinctive strokes. There is a two-stroke cycle not usually used in an aircraft. So, we are going to be looking at the 4 stroke cycle. The 4 stroke cycle begins at TDC -
1. Intake Stroke : here the piston is at the top dead center and is travelling down to the bottom of the cylinder, as it does the pressure reduces in the cylinder and the intake valve is open at this time forcing the fuel-air mixture (charge) into the cylinder. Then the intake valve closes.
2. Compression Stroke : now, the piston is at the bottom dead center, with both valves closed and the charge is in the cylinder. The piston moves upwards, compressing the charge, increasing the pressure thus also increasing the temperature of the charge.
3. Power Stroke : in this stroke the piston at the top dead center and the fuel-air mixture is compressed. Its pressure and temperature are both high, at this point the spark plug ignites and there is a controlled burning of the charge, forcing the piston downwards.
4. Exhaust Stroke : at this point the cylinder is filled with carbon dioxide and the piston is at the bottom dead center. The piston begins to move upwards and the exhaust valve is open. Forcing the exhaust out of the cylinder.
This is how an internal combustion engine works. We will be discussing about it in detail, we will also look at how the four stroke engine is made efficient. We are open to any sort of questions, just leave us a comment and we will get back to you as soon as possible.
