Two Stroke Engines And An Internal Combustion Engineering Essay

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An internal combustion which aid to achieve mechanical work can also be characterised as "TWO-STROKE ENGINE" that utilizes Trapping Valves in the production of mechanical work. It's a project where trapping valves are to be integrated in a two-stroke engine of lotus in order to achieve a high efficiency and reduced carbon emissions as per the required British Standards. The idea of including the valves in a two stroke engine arises from the valves which function in four stroke engine to provide lesser carbon emissions. The trapping valves function in the engine to allow the fresh charge to enter the engine in order to produce energy which in turn pushes the piston up and down which further produces mechanical work after releasing the burnt gases in the engine via the exhaust valves. It was discovered by a Scottish engineer named DUGALD CLERK in 1881, which comprised of a design that had a separate charging cylinder. The two stroke engine cycle is different from the four stroke cycle as the two stroke cycle completes in two strokes whereas the four stroke as the name suggests get completed in four strokes. Basically, four stroke engines is the basis of a two stroke engine. Thus, the advantages of the two-stroke engine over a four-stroke engine can be explained as follows:- (Reference - Kingston University [Internet], Available at: http://www.wisegeek.com/what-is-the-difference-between-a-two-stroke-and-four-stroke-engine.htm ).

Has more get-up-and-go because it fires once every revolution, giving it twice the power of a four stroke, which only fires once every other revolution.

Packs a higher weight-to-power ratio because it is much lighter.

Is less expensive because of its simpler design.

Can be operated in any orientation because it lacks the oil sump of a four stroke engine, which has limited orientation if oil is to be retained in the sump.

The disadvantages of the two-stroke engine can be observed as follows:-

Faster wear and shorter engine life than a four stroke due to the lack of a dedicated lubricating system.

Requires special two stroke oil ("premix") with every tank of gas, adding expense and at least a minimal amount of hassle.

Heavily pollutes because of the simpler design and the gas/oil mixture that is released prior to, and in the exhaust (also creates an unpleasant smell).

Is fuel-inefficient because of the simpler design, resulting in poorer mileage than a four stroke engine.

Has a high-decibel whine that may exceed legal noise limits in some areas, depending on the product and local applicable laws.

Thus, consequently the following report regarding the Design of Trapping Valve would aid to comprehend the design and mechanism of the trapping valve and the function of the two-stroke engine. Moreover, the emissions from the exhaust manifold would decrease from the two-stroke engine as compared to four-stroke engine. Thus, it helps in acquiring the requisite outcomes for designing the trapping valve.

AIMS AND OBJECTIVES

The principal goal of the project is to manipulate the influence of trapping valve in the two-stroke lotus engine via undertaking various calculations and considering the ANSYS (CFX) results. By means of Ansys discrete results can be obtained regarding the performance of the valve in the engine. The key calculations regarding the design of the valve are mandatory. It serves to find the angle and the thickness of the valve which would adequately justify the position in the engine. Also, understanding about various components of the two stroke engine would aid to gain knowledge about the precise working mechanism of the engine. Considering all the factors as mentioned above help in successful accomplishment of the target set in the project and even would help to conclude by identifying the efficiency of the engine.

PERSONAL ROLE AND ACHIEVEMENT

The accomplishment achieved until now is the understanding of the mechanism of the two stroke engine which is as follows:-

Two-stroke engine

The two-stroke engine works as its name suggests in two-strokes. The ignition of the spark takes place in every one revolution whereas comparing it to the four-stroke engine which ignites every two revolution.

The sectional diagram below shows the number of parts of the engine.

They consist of:-

Spark plug

Reed valve

Connecting rod

Crank shaft

Spark plug

''A device containing two Electrodes across which electricity jumps to produce a Spark to fire the fuels charge.'' The centre of the electrode is insulated by insulator to separate it from the ground electrode. There is a gap set between the centre and the side electrode as current is passed spark is generated in the gap and the compressed air-fuel mixture in the combustion chamber ignites. The spark plug is located on the top of the engine.

http://www.auto-repair-help.com/images/articles/articles_0808/spark_plug.gif

Reed valve

Reed valve is located at the intake port of the engine which open and closed under pressure controlling the flow of the air fuel mixture in the crank casing. They are widely used in two stroke engines. When the piston moves up in vacuum is created in the crank casing at this point the reed valve is closed, later with the downwards movement of the piston the difference in pressure the mixture in a crank case moves to combustion chamber. The reed valve opens to give passage to mixture to enter the crank case.

http://www.midwestscooters.com/images/2_STROKE_REED_VALVE_16.95_XGP2S_0440.JPG

Connecting rod

The connecting rod transmits motion from the piston to the crankshaft. The connecting rod is mostly made of steel. It rotates at both the end which allows transmitting motion to the piston at any required angle.

http://img.auctiva.com/imgdata/1/9/3/4/0/5/webimg/149301562_tp.jpg

Crank shaft

Crankshaft is used to transmit linear motion of the piston coming through the connecting rod to rotational moment to the flywheel. The reason to connect the crankshaft to the flywheel is to reduce the pulsating and vibrating effect caused by the connecting rod.

http://www.sschapterpsa.com/ramblings/OB%20images/bad%20crankshaft.JPG

Working

We begin with the compression of the air-fuel mixture in the cylinder. The mixture is compressed by the piston till it moves to top dead centre (TDC).

As the piston reaches the TDC the spark plug ignited the mixture with a spark at the same time a fresh mixture is stored in the crank casing of the engine; with the ignition expands pushing the piston downwards, as the piston moves down the exhaust port is uncovered and the burn gases begin to escape. At the same time the mixture in the crank casing is getting compressed. When the piston moves to bottom dead centre (BDC) the compressed mixture from the crank case of the engine moves to the combustion chamber. When the piston begins the moment from BDC again towards the TDC reed valve open's to allow the fresh mixture to enter the crank casing. On the way when the piston is returning back to the TDC it closed the intake port and then the exhaust port compressing the mixture where again the spark plug ignites it. This repetition of cycle form a chain and a continuous process is from.

http://static.howstuffworks.com/gif/two-stroke-exhaust.gif

http://static.howstuffworks.com/gif/two-stroke-compress.gif http://static.howstuffworks.com/gif/two-stroke-intake.gif

Tuned pipe

A tuned pipe is used as a part of the exhaust system. Tuned pipe is an essential part in the designing of the working of the engine, though they are not part of the engine but are essential to have more fuel efficiency. Mufflers are considered different from these as they are only used to reduce sound. The piston moving up with inertia covers the intake port but still the exhaust port is open. When the piston moves further the fresh mixture in the chamber is also pushed out. This would result in low compression stroke and will affect the performance of the engine and so they are fitted with tuned pipes.

The exhaust port opens up immediately after the ignition and along with the piston moving down the exhaust gases rush out of the exhaust port. During the return of the piston fresh mixture again escapes the combustion chamber. The pipe expands gradually for easy escaping of the gases whereas the end of the pipe has a similar construction facing the other way around continued by a smaller diameter hole to let the exhaust gases out the pipe. As the gases escape from the exhaust port they enter the pipe and explained; moving towards the end back pressure is created as see in the diagram. This back pressure forces back the fresh mixture coming out the exhaust port.

Gantt chart

The following Gantt chart was produced after the satisfaction of the whole group:-

GANTT CHART - The Gantt chart that follows on the next page reviews the tasks which are concluded until this stage as well as the objectives that are yet to be attained.

It commences on the 28th September 2009 with the induction of the project. The project plan reviews the start and finish dates to carry out a particular task which would also operate as an allusion for the advancement of the project. In addition to it, research plays a vital role in the project which purposes an outline which includes: -Research on trapping valves of a two stroke engine, Calculations regarding the design of valves is accomplished and some is thus, far in progress.

Research requires minimum 40 days of the project time commencing 5th October 2009 until 14th December 2009. Furthermore, design knowledge relevant to the project which comprises of:-CFX Analysis (with valve), CFX Analysis (without valve)

Thus, the Gantt chart is as follows:-

DISCUSSION

It can be perceived from the above fragments of the report that for acquiring of the productive outcomes of the trapping valve in two stroke engine, huge amount of research has been performed. The main aim of the project is the introduction of trapping valve in the engine such that more power to weight ratio is obtained and hence, less emissions are observed after combustion of gases in the engine. To begin with, knowledge about two stroke engines is gained and then for the introduction of valves in the engine knowledge about various components forming the engine is gained in order to observe their adjustment with the valves. In addition, ANSYS software is also employed in order to study the effect of trapping valves. This helps in learning about the fluid flow mechanism in the engine and the stresses that are introduced due to the valves. Thus, for obtaining the final outcome of the project that is DESIGN OF TRAPPING VALVE, a Gantt chart is needed to be followed which would hence, help in producing the requisite result.

CONCLUSION

Lastly, it can be concluded by describing about the research work that has been achieved until this phase of the project. It is evident that after intense study about the trapping valves that comprised of essence of trapping valves in working of two stroke engines, discrete components of two stroke engine which together with the valves increase the efficiency of the engine, the research comprises of huge amounts of facts which strengthens the understanding about the project. Subsequently, research about the lotus engine was carried out which comprised of manufacturing of engines (as a group) and finally the structural layout of the engine was scrutinized. Next, the Ansys (CFX) was carried on with and hence, familiarization with the software has been accomplished.

Thus, for the final word for the report it can be said that for the successful achievement of the project Ansys (CFX) is required for the finite element analysis and to study about the fluid flow initiated by the trapping valve in the two-stroke engine. A reasonably fair experience would be gained and a wide understanding can be achieved in creating this engine for future utilization.

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