Aim- The aim of this experiment is to set up an Internal Combustion Engine and measure the different energy contributions to it. The engine itself can be treated as a thermodynamic system. The energy contribution which are not possible to measure can be estimated using a basic steady flow energy equation. The type of internal combustion engine used for the experiment was a Petter four stroke diesel engine.
Objectives- Using the measurements of the different energy contributions to find out how the energy put into a diesel engine is used and where in the engine it is used. Using this information I can come to conclusions on how an engine of this engine can be improved to increase its efficiency.
Background- A diesel engine just like the one used in the experiment are typically used in cars and are manufactured to turn chemical energy (burning diesel), into mechanical energy. This energy is consequently used to move the engines pistons up and down, and as the piston is connected to a crankshaft, the up and down motion of the piston makes the crankshaft rotate. This rotation is what is used to make wheels of cars, motorbike etc rotate.
Petter four-stroke diesel Engine
Stoke 1 (The intake stroke)-The piston (the metal component which moves up and down a cylinder) starts at the top of the cylinder. Then intake valve opens and allows air to enter, and therefore the piston moves down, until the cylinder is filled with air.
Stroke 2 (The compression stroke)- The piston moves back up the cylinder to compress the air inside it. Compression increases the air pressure and therefore the temperature increases to approximately 400 degrees.
Stroke 3 (The combustion stroke)-When the piston reaches the top and the air is fully compressed, the fuel is injected it. This is enough for the fuel to be combusted and the energy created by this combustion moves the piston back down the cylinder, this movement produces the power to drive the machine the engine is connected to.
Stroke 4 (The exhaust stroke)- After the piston gets to the bottom of its movement dow the cylinder, the exhaust valve opens and the exhaust escapes to go out the exhaust pipe.
The results taken in the experiment would be useless on their own and they would have to be put into the basic steady flow energy equation. Qr-Wrx = -ṁf *CV + (ṁa + ṁf) * ( h’pc + ha)
However in order to include the possibility of fuel not being fully combusted, its ideal to change -ṁf *CV with -ṁf *(CV-FL). With FL representing the proportion of unburnt fuel energy is not been applied due to incomplete combustion.
Also as Qr represents the total energy that is lost to the cooling water and the engines surroundings due to the components heating up, we can have; Qr = -ṁw*Cpw* (Tout – Tin) + Qrn
Also ‘( h’pc + ha)’ can; = Cpe*(Te – Tin)
Taking all of this into consideration, and taking the unmeasurable units ( Qrn - ṁf*FL = ṁf *CV – (ṁw*Cpw* (Tout – Tin) + Wrx + (ṁa + ṁf) * Cpe*(Te – Tin))) to one side, you get a final energy equation of; Qrn - ṁf*FL = ṁf *CV – (ṁw*Cpw* (Tout – Tin) + Wrx + (ṁa + ṁf) * Cpe*(Te – Tin))
The four different parts of the right hand side of the equation has to be calculated separately and the pulled backed together at the end.
List of Symbol Definitions
Qr- the amount of energy which is transferred to the cooling water and lost to the surroundings.
Qrn- the rate at which heat energy is lost from hot engine components.
Wrx- the rate at which work is done within the engine (power). ṁf- the rate at which the fuel is burnt at by the engine ṁw- the cooling mass flow rate ṁa-the air used for combustion mass flow rate
CV- the fuels lower calorific value
FL- the proportion fuel energy which is accounted for due to incomplete combustion h’pc- specific enthalpy of the products being combusted. h’a- specific enthalpy