Explain in detail, the differing operating cycles inherent in two unrelated i.c (internal combustion) engines
An internal combustion engine differs in operation depending on which fuel it is being run of because petrol and diesel have different properties.
Diesel And Its Properties
- Diesel is obtained from crude oil via 3 processes separation, upgrading and conversion
- The initial boiling point for diesel is around 125 degrees (c)and its final boiling point around 400 degrees (c)
- Diesel also contains sulphur the more sulphur it contains the more electricity it can conduct insufficient electric conductivity is potentially a safety hazard as it could lead to a build up of static charge during the bulk transfer of fuel however it’s not very high risk in a motor vehicle because of the low velocity of fuel that gets transferred
- Needs to be inject in to the combustion chamber at high pressure so that the amount of diesel is always the same and so that the correct amount of diesel reaches each combustion chamber at the correct time
- Diesel is not flammable this is why a glow plug is required to heat the diesel up on a cold start this is also another reason why diesel had to be forced into the combustion chamber under high pressure
Petrol And Its Properties
- Has and lower boiling point than diesel
- Petrol is flammable and there for can be ignited using a spark unlike diesel
- Petrol is not as dense as diesel they both are produced from crude oil but is more refined than diesel
- Reasons for differences in an ic engine running on petrol in oppose to diesel
Because of the different properties in petrol and diesel the parts and configuration of ic engines and the way they are run varies. For instance a modern diesel will have a fuel rail located on top of the combustion chamber which depending on how many cylinders will have a row of high pressure injectors for instance a 4 cylinder would have 4 injectors one per cylinder. Now this would be the case in a petrol engine but the injectors would operate under much lower pressures and therefore the pipes that go to each injector are different. Often the pipes leading from the fuel pump to the injector on a diesel engine are made out of copper as it is a material that handles well under pressure but in a petrol engine the pipes are usually just rubber or PVC depending on the requirements they need to meet. A diesel engine only take in air, and shortly before the peak amount of compression, a small quantity of diesel fuel is sprayed into the cylinder via a fuel injector at high pressure that allows the fuel to instantly ignite due to higher pressures and heat. A petrol engine uses a different method to ignite the fuel source because petrol is flammable it can be ignited using a spark the petrol is injected into the combustion chamber under relatively low pressure but before it reaches the chamber it becomes in contact with a spark plug which ignites the fuel forcing the piston down this causes compression which forces the piston back up creating the stroke in this case a 4 stroke cycle. Both ic engines in this case use the 4 stroke cycle the only difference being the way the fuel is ignited, which in turn gives u the combustion stroke which starts the 4 stroke cycle.
Task 2- Evaluate the vehicle design, and therefore the performance implications of a particular choice of engine configuration and layout
Ferrari use a dry sump system in appose to a baffled sump system which is more commonly found on an ic engine. This is because a baffled sump takes up a lot of space and has a large depth this is because in a baffled sump system all the oil is stored in one place. A dry sump works by having a separate oil reservoir. There is a shallow oil reservoir usually mounted on the underneath of the engine and then a separate oil tank is located somewhere else in the engine bay. A pump helps supply the reservoir tank with oil from the main oil tank and then a scavenge pump helps to reticulate the oil back to the oil tank via pipes ensuring a constant flow of oil gets supplied to the engine at all times.
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The main advantage of the dry sump system is that it means an engine can be mounted lower to the ground as meaning the car can have a lower centre of gravity improving the cars overall performance and handling this is why dry sump systems are most commonly found on race cars and performance cars. There are downfalls to dry sump systems they require more piping and to oil reservoirs meaning the manufacturing costs are higher than they would be if a baffled sump system. Ferrari also mount their engines primarily in the middle of their cars the main reason for this being that you can achieve a perfect 50 50 weight distribution meaning that the cars handling is as good as it can be as all the weight is shared across the chassis evenly. It also means that under heavy breaking the car wont nose dive because there isn’t more weight in the front of the car than the rear. The main downfall to having a middle mounted engine is that u can only really fit 2 seats into a car and that you lose a lot of the practically of the vehicle but the gain in the performance of a vehicle with a middle mounted engine more than makes up the practicality lost.
task 3- explain the function, operational and construction of the main internal components/ assemblies of a particular type of I.C engine
In an ic engine there are several different components which are critical for the running of the engine here I am going to name and explain what the main internal components do and there functions.
Valves- in a common 4 cylinder 16valve engine there is 4 valves per cylinder mean 4valves times 4 cylinders 16 valves. 2 of these valves are inlet valves and the other 2 valves are outlet valves, the inlet valves allow the injected petrol or diesel to enter the combustion chamber at regular intervals these intervals are determined by the cam shaft. The outlet valve does the opposite of the inlet valve when the outlet valve opens it gets rid of the gases and deposits created from the 4 stroke cycle.
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Pistons-the function of the piston is to compress the mix that enters the combustion chamber this happens because as the mix of fuel enters that enters the chamber when ignited forces the piston from tdc down to bdc then as the piston starts to rise from bdc back up to tdc this creates compression then as the piston rises the outlet valves open and the gases causes from the combustion stroke exit through the valves under pressure and are exited from the car via the exhaust
Drive belt- A belt is a loop of flexible material used to link the 2 shafts of an engine together mechanically. In an ic engine the belt has to be timed so that both the cam shaft and the crack shaft are turning at the exact rite time so they can carry out their function efficiently.
Cam shaft- The cam shaft only function is to ensure that the valves open and close at the correct time it is essentially a metal shaft that has metal pear shaped components placed along it at regular intervals the reason for these pear shaped metal components is that when the cam shaft is turning via the drive belt each pear shaped component corresponds with the rocker cover of the a valves the pear shaped component pushes one side of the rocker cover down which compresses a spring located underneath the rocker cover which in turn pushes the inlet valves open. The cam shaft then continues to turn allowing the inlet valves to close. Then the other pear shaped components correspond with the other side of the rockers cover then when they come in contact with the rocker cover push down the outlet valves this is all done to a precise timing which is determined from the drive belt.
Crank shaft- The crank shaft is what determines the movement of the pistons the shaft is usually driven from the drive belt and the big end of the cam rod connects the piston to the shaft this shaft converts the rotational motion of the shaft into a vertical motion so that the pistons can move up and down in the cylinders.
Cam rod- the cam rod is the rod that connects the piston to the crack shaft it does this via a big end and a small end the big end connects to the crank shaft and the little end connects the head of the piston to the rod the piston heads are usually connect to the cam rod using a pin.
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