Combustion Heat And Mass Transfer Combustion Engine Engineering Essay

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Engine is an important part for a car. The essential process that causes the engine obtains the mechanical energy is the chemical energy of fuel burned in a combustion chamber. In this report, we will research and discuss the basic concept behind an engine and furthermore into detail about types of combustion engines and types of fuel which are used in a sport car.

Nowadays, combustion engine can be divide into two categories which is internal combustion engine and external combustion engine.

An internal combustion engine is the engine that operates by burning its fuel inside the engine or we can say that combustion process take place internally. Normally, there are few types of internal combustion engines are used in general, which are:

Reciprocating engines - normally known as piston engine; two strokes or four strokes engine.

Rotary engines - such as the Wankel engine, do not have piston.

Sustained combustion engines - which included gas turbine and jet engine.

External combustion engine

An external combustion engine is the engine that operates by heating a working fluid with combustion of an external source through the engine wall or a heat exchanger then the fluid is expanding and acting on the mechanism of the engine to produce motion and usable work in the engine. There are few types of external engines are being used which are Stirling engines and Steam engines.

Nowadays, the combustion engine that used in the sport car is an internal combustion engine like the photo shown at below.

Basic Concept of Combustion Engines

The basic concept of a combustion engine is using the exothermic chemical process of combustion in the engine to produce mechanical energy and motion. During the process, the fuel will reacted with oxygen from the air; of course it will produce other oxidizers such as nitrous oxide. The result of combustion process will produce a great quantity of heat, as well as the production of steam and carbon dioxide and other chemicals at very high temperature.

The combustion process can be converted into a simple word equation:

Fuel + Air → Heat + Water + Carbon dioxide + Nitrogen

Therefore, in case of the expansion of high temperature and pressure of gases those are produced by the combustion in the cylinder of the engine, it will apply a force to the movable component of the engine (pistons or turbine blades). Normally an internal combustion engines must achieve ignition in their cylinders to create combustion, so the engines will use either a spark ignition (SI) method or a compression ignition (CI) system.

Typically, sport cars are using the four stroke engine, which is an internal combustion engine. There have four steps in this process:

Intake stroke

The piston starts at the top in the cylinder, and the intake valve opens, then the piston will moves down, because of the expansion of volume and reducing of pressure in the cylinder, a mixture of air and fuel is forced to fill in the cylinder through the intake valve. This is the intake stroke.

Compression stroke

Then the intake valve closed and the piston moves back up to compress this air-fuel mixture. This process will make the explosion more powerful.

Combustion stroke / Power stroke

When the piston is near the top of its stroke, the spark plug emits a spark to ignite the air-fuel mixture or the mixture will ignited by the heat and pressure of compression in a compression ignition system. The mixture in the cylinder explodes, then the pressure of burning gases drive the piston down.

Exhaust stroke

Once the piston hits the bottom of its stroke, the exhaust valve opens and the piston push the product of combustion leaves the cylinder through the exhaust valve.

Starting position intake stroke compression stroke

Ignition of fuel power stroke exhaust stroke

Types of the engines

There are a few types of internal combustion engines, as shown at below:

Reciprocating engines

E & I - Exhaust camshaft & intake camshaft

V - Valves

S - Spark plug

P - Piston

R - Connecting rod

C - Crankshaft

W - Water jacket for coolant flow

In the type of reciprocating engines, there have two designs are used generally, which are:

Four stroke engine: The four stroke engine was first demonstrated by Nikolaus Otto in 1876, so it also known as an Otto- cycle. The four-stroke internal combustion engine is the type that most widely used in engine, especially used for automotive, truck and aircraft today. In this design, the four steps of engine process take place within four stroked, or two cycles of piston motion.

Two stroke engine: The two stroke engine has a similarly function to the four stroke engine. It is simple in construction, but complex mechanical ideas are used in its process, which uses both the crankcase and the cylinder to achieve the ideas of the Otto cycle by using only two strokes of the piston. This type of engine is used in recreational applications or which only require a small, inexpensive, and simple mechanically motors like chainsaws, jet skis, small motorcycles, and etc.  In this design, the steps of engine process just take place within two stroked, or one cycles of piston motion.

Intake

The air- fuel mixture is forced to drawn into the crankcase, because of the low pressure that is created by the piston move upward to the stroke.

Crankcase compression

During the downward stroke, the poppet valve is forced to close by the increased of crankcase pressure. The air- fuel mixture is compressed in the crankcase.

Transfer/Exhaust

Toward the end of the stroke, the piston exposes the intake port, allowing the compressed fuel/air mixture in the crankcase to escape around the piston into the main cylinder. This expels the exhaust gasses out the exhaust port, usually located on the opposite side of the cylinder. Unfortunately, some of the fresh fuel mixture is usually expelled as well.

Compression

The piston then moves upward, and compresses the air- fuel mixture. At the same time, another intake stroke is happening below the piston.

Power

Near the top of the stroke, the spark plug ignites the air- fuel mixture. The burning fuel expands, driving the piston downward, to complete the cycle.

Rotary engines

This concept of internal combustion engine was first developed by a German engineer Felix Wankel in 1950, so the rotary engines can also known as Wankel engine. This kind of engine is classified as "four phase" engine but not "four stroke engine", because it does not have pistons, in which the piston and cylinder were replaced by a triangular rotor turning in a roughly ovoid chamber. The engine phases occur in the spaces between the rotor surfaces and the housing. This engine provides three power 'strokes' per revolution per rotor and giving it a greater power-to-weight ratio than piston engines.

Intake

The air- fuel mixture is drawn in the intake port during this phase of the rotation.

Compression

The mixture is compressed here.

Power

The mixture ignited here, driving the rotor around.

Exhaust

And the exhaust gases are expelled here.

Sustained combustion engines

Gas turbine and jet engine

It follows the theory of Brayton cycle. Gas turbine and jet engine is a rotary engine that works out energy from the flow of the combustion gases. Firstly, a mixture of air and fuel are added into a combustor and ignited. The combustion process that take place in the combustor will increase the temperature, velocity, pressure and volume of the combustion gases, then the gases will flow through a nozzle and hit on the turbine's blade and turning the turbine directly. By the way, the turbine will work out energy due to the turning of turbine. Normally, they are using in air travel industrial.

Diagram of gas turbine process

Diagram of Brayton cycle

Here, we are discussing about the external combustion engine:

Stirling engine

Beta type Stirling engine (known as one cylinder Stirling engine)

A Stirling engine is an engine that using alternately compressing and expanding of a fixed quantity of air or other gas at different temperatures to convert the heat energy to mechanical energy and motion.

Expansion

Heating the end of the cylinder, the gases or working liquid will expand and drive the piston outward.

Transfer

Flywheels that connect to the crankshaft provide a momentum carries the crankshaft the next quarter turn. The gas is transferred around the displacer (shown in blue) to the cool end of the cylinder.

Contraction

The hot expanded gas has shifted to the cool end. Then the gas is cooled and contracted and draws the piston inward.

Transfer

Flywheel momentum carries the crank another quarter turn, moving the displacer and transferring the gas back to the hot end of the cylinder.

There have another one type of Stirling engine. It used the same idea but different in its structure and arrangement.

Alpha Cylinder Stirling Engine (known as two cylinder Stirling engine)

It was developed by Rev. Robert Stirling of Scotland in 1816. The Stirling is a very simple engine, and was often operate at a safety condition, because there's less risk of a boiler explosion when compare with other combustion engine.

Diagram of Alpha Cylinder Engine

Comparison of the combustion engines

Capabilities

Four stroke engine

Two stroke engine

Wankel engine

Gas turbine and jet engine

Stirling engine

Combustion process takes place

Internally in the engine

Internally in the engine

Internally in the engine

Internally in the combustor

Externally of the engine

Kind of fuel use in

pure, high-quality liquid or gaseous fuel

pure, high-quality liquid or gaseous fuel

pure, high-quality liquid or gaseous fuel

pure, high-quality liquid or gaseous fuel

Any fuel that can burned

Byproduct

Carbon dioxide, nitrogen, nitrous oxide

Carbon dioxide, nitrogen, nitrous oxide, carbon monoxide, unburnt hydrocarbon

Carbon dioxide, nitrogen, nitrous oxide, carbon monoxide, unburnt hydrocarbon

Carbon dioxide, nitrogen, nitrous oxide

Depend on the fuel used, normally it used as heat pump, so no byproduct will be produced

Engine cycle

Otto cycle

Otto cycle

Otto cycle

Brayton cycle

none

Cost

Expensive of manufacture but fuel efficiency

Less expensive in manufacture but fuel inefficiency

Less expensive due to simply design

Most expensive due to the stronger and more heat resistant

High capital cost but low maintenance cost

Power to weight ratio

High

Very high

Very high

Very high

Low

Safety

Non- safety because of the explosion in piston

Non- safety because of the explosion in piston

Non- safety because of the explosion in piston

Non- safety because of the explosion in combustor

Safety, there's no risk of a boiler explosion

Application

Automobile, truck, aircraft, and etc

recreational applications or application require a small and simple mechanically motors

Automobile, aircraft, and etc

Rocket, tank, naval, commercial use and etc

Stirling cryocoolers, Heat pump, Low temperature difference engines and etc.

After comparison of few different types of engine, we can have some conclusion about choosing the suitable engine for the sport car.

Firstly, we will disqualify the Stirling engine. Not only it is an external combustion engine, but also it cannot provide enough power to sport car.

Secondly, we will not consider about the two stroke engine. The reason is a two stroke engine cannot supply the enough energy and power for a sport car. Although the two stroke engine has the high power to weight ratio and less expensive in manufacture the engine, but it is fuel inefficiency and cannot supply enough engine power to create an efficient sport car.

Thirdly, we look for the gas turbine. Although gas turbine can provide the power needed but due to its engine need a strong and more heat resistant material and it will affect the speed of the sport car, so we will draw out the gas turbine engine.

After that, we only have the left two types of engine, which are four stroke engine and Wankel engine. Both of the engines are usually used as a sport engine today. Their capabilities are most suitable for running a sport car engine. But after the comparison, we found that there was some disadvantage for using the Wankel engine. Firstly, an Wankel engine provide a high rpm power, so it need a large amount of fuel to go on the combustion process and it will cause the poor fuel efficiency and exhaust emissions. Secondly, the design of the Wankel engine requires several sliding seals and a housing that is built in different degrees. These materials inside the engine lead to a very high incidence of loss of sealing, when the engine works through the heating and cooling cycles at a high speed of rotating.

So, we choose the four stroke engine as a sport car engine, because it can make up the whole limitation from others type of engine.

Types of fuels

The propellants that most automobiles used today are gasoline or diesel combustion engine. And we know that those are the headstream that causes the air pollution or global warming today. So we do a lot of effort to improve or exchange the existing propulsion technologies like development of hybrid vehicles, and electric and hydrogen vehicles, which do not release the pollution to the air. Nowadays, there are some fuel used mostly, which are:

Petroleum fuel

Bio-fuel

Hydrogen

Electric

Solar

Steam

Petroleum Fuel

Gasoline

Gasoline is a petroleum-derived liquid mixture.It is a natural by-product of the petroleum industry, which is produced by distillation. Gasoline engines have the advantage over diesel, because it is lighter and able to work at higher rotation speeds, so they always are the first choice for using in high-performance sports cars. Under the continuous development of gasoline engines for many years, it has been produced improvements in efficiency and reducing pollution.

Diesel

Diesel is a hydrocarbon mixture. It is produces from petroleum by the fractional distillation of crude oil. Diesel engines are heavier, noisier, and more powerful at lower speeds than gasoline engines. They are also more fuel-efficient and are used in heavy road vehicles, some automobiles, ships, railway locomotives, and light aircraft.

Diesel is unmixed with water

Bio - fuel

Bio-fuel has widespread use as an automotive fuel. Most bio-fuel has less energy than gasoline so it was usually blended with gasoline. The reason is to increase octane in the gasoline, to improve emissions and used as a substitute to petroleum based fuel, because it can be made from agricultural crops. The examples for bio-fuel are bio-butane (replace gasoline), biodiesel (replaces petro diesel), bio-ethanol, bio-methanol and biogas.

Bio-fuel is less expensive than diesel

Hydrogen

This kind of car used the hydrogen in one of two methods: combustion or fuel-cell conversion. In combustion, the hydrogen is going through the same method as traditional gasoline cars in engine. In fuel-cell conversion, the hydrogen is turned into electricity through fuel cells which then powers electric motors. If the technology of using hydrogen fuel cell becomes widespread, the technology of internal combustion engine will be eliminated. The disadvantage of hydrogen is the problem of storage. Liquid hydrogen has a very low density (14 times lower than water) and requires heavy tankage. But the advantage is there have the only one byproduct from the spent hydrogen which is water.

Hydrogen fueling

Battery-electric power

Battery-electric vehicle is the electric car which main energy storage is in the chemical energy of battery. The first electric cars were built around 1832 that is appeared early before internal combustion engine cars. It is a type of car that utilizes electric motors and motor controllers instead of an internal combustion engine. Electrics were considered superior that time because of the silent nature of electric motors when compare with the internal combustion engine. Currently, electrical power is stored in a battery packs which carried by vehicle. Another method of storage that may use in the future includes the use of ultra capacitors, or stores the energy in a flywheel.

Solar power

A solar car is an electric vehicle powered by solar energy obtained from solar panels on the car. Solar cars are not a practical form of transportation, because the energy that absorb from the surface is insufficiency compare to the sized and shaped vehicle. The advantage is a solar car is using a type of renewable energy, and it can solve the problem of pollution and global warming.

Solar vehicle design

Capabilities

Petroleum

Bio - fuel

Hydrogen

Electric

Solar

Energy produce

High energy produced

High energy produced

High energy produced

Moderate energy produced

Low energy produced

Byproduct

Carbon dioxide, nitrogen, nitrous oxide

Carbon dioxide, nitrogen, nitrous oxide

Water

none

none

Cost

Inexpensive for overall

Inexpensive

Expensive for the part of instrument

Moderate

Expensive to built the solar panel

Renewable

Non-renewable

Renewable

Renewable

Rechargeable but not renewable

Renewable

Density

800 - 1000 kg/m3

Depend on the biofuel that used

0.090 grams/liter at 0 °C and regular atmospheric pressure

--

--

Power to weight ratio

High

High

Highest

Low

Low

Safety

Non- safety, because it is flammable

Non- safety, because it is flammable

Non- safety, a liquid hydrogen is cold enough to freeze air

Safety

Safety

Storage

Normal petroleum storage tank

Normal storage tank

Three times the size of a normal petroleum storage tank

Electric battery

Solar panelComparison of the fuel

We are totally agreed with petroleum or bio-fuel to be a fuel for sport car.

Firstly, we will not consider the solar energy to be the fuel for a sport car, because it needs a large area of solar panel to absorb energy and this will increase the weight of sport car and affect the speed directly. For another reason is solar energy cannot provide the efficient energy for a sport car.

Secondly, we will forget about the electric power and hydrogen power. Both of them need a large storage to store the energy or fuel. Another reason for abandon electric power is because it cannot work for a long time. For hydrogen power, because the insulator cannot be perfect in actual, the hydrogen will evaporate gradually when using for a long term.

Lastly, the reason why we choose petroleum and bio- fuel is they overcome the disadvantages of others fuel. People would say that these two kind of fuel are the headstream that cause the global warming and pollution, but there have some group of professional people working to improve the capability and performance of the fuels and it seems that the pollutions are under control.

Conclusions and Future Works

Conclusion

In the engine system, there are two categories which are internal combustion engine and external combustion engine. Although there are two categories of engine, but their concepts that apply to the engine are the same, which is combustion process.

There are few types of engine in the category of internal combustion engine. Maybe there will have some engines we are not mention here, but what we have mention is the most usually used engine and the basic idea of those engine.

In the report and research, we can get that the propeller engine for a sport car is an internal combustion engine. It overcome the problem of others type of engine and we can found that four stroke engine is the most usually engine used for sport car in our life.

In the fuel discussion, there are lots of fuels using today, but the most we seen is petroleum, which becomes a common fuel that we use today. Although the capabilities of others fuel will more efficient to apply but due to the politics' issues and the customer need in the market, there is something hard to change. And because of the improvement of petroleum, people are more confident with it and using it.

We want to specify that there is a complex system for the sport car and we are just discussing two factor here, which is type of engine and type of fuel only, and it is not enough for develop a nice and efficient sport car. There still have a lot of factor that will affect the performance of sport car like type of type, the design of car, air flow and etc.

Future Works

Nothing will faster than the future. Now, the trend of fuel is tending to improve the petroleum. Beside the way, people are looking for something that can substitute the petroleum and reliable, something that can solve the pollution issue, and something that can renewable and low-costing.

A few years before, there was nobody realizes that hydrogen can provide energy to move the car, but now, it already applied in our life. People always looking for the fuel which is exhaustless, renewable and clean, this is one of the natures of human.

Now, nuclear power technology is already occurs in our life. It just needed a small amount of uranium and after nuclear fission; it can come out with a large amount of energy. It can always satisfy a great deal of demand of human. Maybe this kind of fuel will apply to the vehicle in the future. And it still has a lot of work need to do.

There is a kind of car called "hybrid" or "dual-drive". This kind of car applied two different type of engine in a car. The vehicle can be driven by the engine or an electric motor or both at the same time. It lets the automobile not to depend on an internal combustion engine at all. And we are looking for more creative and reliable engine will come in the future to overcome the barriers and disadvantage of engine used today.

Future vehicle, illustration by Ian Whadcock

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