Dynamic Analysis Of A Petrol Engine


Dynamic Analysis of a Petrol Engine as the name suggest, is the analysis of the pressure and the crank angle of the petrol engine according, to the processes going on in the combustion chamber. Petrol engines are those Internal Combustion Engines via which combustion of fuels (generally fossil fuel) is possible with the help of an oxidizer such as air. The process that goes on inside the combustion engine is that after the expansion (reaction) of the fuel with the air, the expansion of the gases produces large amount of force which in turn moves the moveable component in the engine such as piston which further helps in the production of useful mechanical energy. It was in 1876 that Nikolaus Otto working with Gottlieb Daimler and Wilhelm Maybach developed a practical four stroke petrol engine (REFERENCE Kingston University [Internet], Available at: http://en.wikipedia.org/wiki/History_of_the_internal_combustion_engine). Also, the engine comprises of discrete components which build up the complete engine. Subsequently, the elements can be described as follows:-


The four stroke petrol engine has predominantly four fundamental phases that replicate every two revolutions. Thus, the elementary processes are as follows:-

  1. INTAKE The foremost stage from the four phases of the functioning of the petrol engine is the consumption of the air-fuel mixture from the environment via the intake manifold. Thenceforth, transfer the mixture to the combustion chamber. The combustion chamber comprises of the piston and the connecting rod (also known as con-rod) which facilitates the second stroke of the process termed as Compression.
  2. COMPRESSION The succeeding stage of compression that comprises of pressurising the air-fuel mixture. This helps in decrement of the volume of the mixture thereby increasing the temperature and bringing the mixture to a point of bursting and hence, producing energy. In addition, the piston moves upwards where the spark plug at the top ignites the compressed mixture which in turn makes the piston move downwards again giving rise to power stroke.
  3. POWER STROKE Subsequently, the power stroke arise as a result of compression of the air-fuel mixture. During the power stroke the expansion of the gases take place and henceforth, deflagration (expression used to describe subsonic combustion going on in the combustion chamber and propagating through thermal conductivity) occurs. (Reference Kingston University [Internet], Available at: http://en.wikipedia.org/wiki/Deflagration).
  4. EXHAUST Finally, the exhaust phase of the process come into play via which the combustion products are expelled out of the exhaust manifold and latter through the tailpipe of the car.

Thus, the following report facilitates brief understanding of the operation and components of petrol engine and enlightens about the effective management of the project. In addition, the graph between the pressure and crank angle would also be deliberated. Also, the designing of petrol engine is discussed. Thus, the following report would facilitate in productively acquiring the aim of the project (Dynamic Analysis of Petrol Engine).


The chief goal of the project is to produce the dual combustion cycle plot which comprises of a graph between the gas pressure inside the combustion chamber and the crankshaft angle. Moreover, in order to create this graph knowledge about engine design is required. Thus, for designing the engine assembly awareness of the Engine Mechanism Analysis is mandatory which is carried out via originating an excel spread-sheet program. This program requires the understanding of indicator diagram for an Internal Combustion Engine (Petrol Engine). Furthermore, information concerning the indicator diagram for the pressure-crank angle is essential. Moreover, a CAD model is also mandatory after the possible outcomes that are obtained from the engine design calculations. Consequently, the subsequent report would assist in getting through the course of procedures essential for the successful completion of the project.


The progress that has been carried out until this stage is that reasonably fair amount of research work has been accomplished. Research comprises of the knowledge about the functioning of the petrol engine and its diverse constituents that it is made out of. In addition, the Indicator Diagram for the Internal Combustion Engine had also been looked through. Corresponding, to the amount of data gathered so far a reasonable amount of work has also been done for the excel spread-sheet. Moreover, a Gantt chart has also been sketched which aid to execute the tasks in precise amount of time and hence, achieve the vital aim. The progress done thus far is as underneath:

  • Research To approach the required aim of the project, the project was initiated via intensely exploring the four stroke engine cycle. Followed by the four stroke engine cycle data, information was expanded on different components of the engine.

Thus, the detailed four stroke cycle is rationalized as below:-

FOUR STROKE ENGINE CYCLE The four stroke cycle is described below:

Prior to the functioning of the four stroke engine discrete components of the engine are ought to be elaborated. The adjacent illustration, aids to understand the constituents of the four stroke engine in much more in detail. (Reference of illustration Kingston University [Internet], Available at: http://autoclub.rso.siuc.edu/frange.html ). The intake valve initiates and permits the mixture to enter the combustion chamber. Next, the exhaust valve opens up to allow the mixture of burnt gases leave the combustion chamber. During the process of combustion the spark plug ignites the mixture which creates excessive pressure on the piston head and hence, it is forced to move downwards. The piston (as shown in the illustration) moves up and down in a to and fro motion. The force exerted on the piston head is transferred to the connecting rod which is attached between the piston and the crankshaft. Thus, the crankshaft is responsible for the rotating motion of the piston and the connecting rod.

INTAKE STROKE During the intake stroke of the piston the air-fuel mixture is forced into the combustion chamber by the atmospheric pressure. The intake valve opens for a precise period of time to let the mixture pass through the intake valve. As the piston begins moving from the TDC (Top Dead Centre) in the downward direction during the intake stroke a vacuum is created above the piston head which is simultaneously occupied by the air-fuel mixture entering through the intake port via the intake valve. The figure shown besides justifies the explanation above evidently. (Illustration below and data referred from Kingston University [Internet], Available at: http://autoclub.rso.siuc.edu/frange.html ).

COMPRESSION STROKE As a result, of the Intake Stroke, Compression Stroke comes into play. The outcome of the intake stroke forces the piston to attain a position at BDC (Bottom Dead Centre), but during the compression stroke the piston commences to move in upward direction towards TDC. At this very stage, both the intake and the exhaust valve are shut and hence, the air-fuel mixture is set off for compressing. Consequently, the pressure of the mixture is increased and the volume of the original mixture is declined to nearly one-tenth of the original which thereby, increased the temperature of the mixture. The figure besides describes the compression stroke. (Illustration below and data referred from Kingston University [Internet], Available at: http://autoclub.rso.siuc.edu/frange.html ).

POWER STROKE Subsequently, after the piston attains a position at TDC back again after travelling from the BDC and compresses the mixture completely, the spark plug situated at the top of the combustion chamber ignites the compresses air-fuel mixture via a spark after getting a high voltage wave from the ignition mechanism. The mixture then burns instantaneously and a pressure of approximately 600 psi is attained inside the cylinder. Yet again, the piston is pushed back down from TDC towards BDC because of the forces generated due to combustion of the gases via spark plug. Also, this power is transmitted to the connecting rod and further to the crankshaft which in turn brings mechanical outcome and hence, makes the car move. The following image rationalizes the above explanation. (Illustration besides and data referred from Kingston University [Internet], Available at: http://autoclub.rso.siuc.edu/frange.html ).

EXHAUST STROKE As soon as the BDC is approached via the piston due to the power stroke, the exhaust stroke initiates which further brings the exhaust valve into operation. Thus, during the exhaust stroke again the piston moves towards the TDC, expelling the combustion products obtained as a result of the power stroke via the exhaust valve which further travels through the exhaust manifold and leaves the engine. In addition, the exhaust valve open for a precise period of time within which the all the exhaust gases are expelled and a vacuum is created again in the combustion chamber after the piston reaches TDC travelling from BDC. Thus, the cycle again recurs with the initiation of the intake stroke. The adjoining figure justifies above data. (Illustration alongside and data referred from Kingston University [Internet], Available at: http://autoclub.rso.siuc.edu/frange.html ).


CAMSHAFT The location of the camshaft in the engine depends on the position of the crankshaft. Particularly there are two modes of placement of camshaft. One is on the top of the cylinders and the other is via making use of pushrods and rockers. Camshaft can be constructed via utilizing either forged steel or cast steel. The image is alongside (Camshaft image Reference- Kingston University [Internet], Available at: http://www.kennedysdynotune.com/images/Camshaft3.jpg ).

PISTONS The piston is situated in the combustion chamber and is a cup-shaped cylindrical element capable of moving up and down in the combustion chamber via connecting rod. In addition, it consists of rings which help in preventing the escaping of gas on top of piston head and also, helps in distributing the requisite amount of lubricant on the cylinder wall. The figure alongside shows pistons (Reference - Kingston University [Internet], Available at: http://www.allproducts.com/manufacture100/shangdeautopart/product1.jpg ).

CONNECTING ROD It is also known as "Con-rod. It forms a link between piston and crankshaft and even helps in converting the force created over cylinder head into rotational motion of crankshaft via transferring the energy. It is made of forged steel and is connected to the piston through a gudgeon pin and is assembled with the crankshaft as shown in the figure alongside. (Reference Kingston University [Internet], Available at: http://www.metaldyne.com/metaldyne/images/sections/engine/products/connecting_rod_270.jpg )

CRANKSHAFT Crankshaft is situated at the bottom of the connecting rod and helps in converting the linear piston motion into rotational motion. It is made out of cast steel or forged steel due to compact dimensions and better damping characteristics. Also, carbon steel is utilized for building a crankshaft. It also helps in driving the camshaft with the help of timing belts. A picture of crankshaft is shown alongside. (Reference Kingston University [Internet], Available at: http://www.tinindianperformance.com/images/forged_pontiac_crankshaft_b.jpg ).


Hand Calculations


Gantt Chart

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 12th October 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 dynamics analysis of petrol engine
  • Calculations regarding the project are accomplished and some is thus, far in progress.

Research requires minimum 40 days of the project time commencing 15th October 2009 to date inclusive of examinations dates. Furthermore, calculations relevant to the project which comprises of:-

  • Displacement of piston
  • Crank angle versus pressure plot

Last but not the least, a dissertation which will include the entire evident endeavor made in the course of the year on order to meet the desired results and aims commences of the April 2010 to 16th May 2010.


It can be noticed from the above progress that for the smooth advancement of the project the Gantt chart is obligatory to be followed. According, to the present circumstances targets regarding the research work have been accomplished. Consequently, the research involves the operation of the four-stroke cycle of the petrol engine, the numerous different components that the petrol engine comprises off. Also, the indicator diagram for the internal combustion engine (petrol engine) has been scrutinized and has been described in the appendix of the report. Though part of calculations have also been performed for achieving the indicator diagram for mathematical modeling purpose yet the calculations aren't complete. They involve computation of piston displacement by hand and via excel spread-sheet program for the required engine with specification of crank radius as 28.50 mm and con-rod length of 112 mm. In addition, quantities such as pressure and volume inside the cylinder for a given crank angle, gas force acting on piston crown, con-rod force, torque acting on the crankshaft and power being developed in an engine for a given engine speed can also be predicted whilst the completion of the calculations. These calculations would further help to explain various graphs between gas pressure & crank angle, gas force & crank angle, con-rod force & crank angle, engine torque & crank angle and power versus the crank angle.

Thus, for the effective outcome of the project the Gantt chart and the knowledge about the project would be the important keys. Additionally, the final pressure versus crank angle plot that is vital for the project and yet to be approached is as follows:


To conclude with the report, it can be perceived that from the research carried out until this stage the functioning of the engine has been justified. Also, the knowledge about various components helps in understanding the construction of the petrol engine. The indicator diagram for petrol engine (Otto Cycle) makes the research more rationalized by providing information about the pressure and temperature at discrete points in the T-S plot that is temperature versus entropy plot or the P-V plot that is the pressure versus volume plot. In addition, the hand calculations so far carried out help in identifying the relative position of piston when the forces are acting on the crown of the piston. The excel spread-sheet program is an evidence of verifying the hand calculations carried out so far.

Thus, it can be finally concluded by saying that the final target of achieving the plot between pressure and crank angle is to be approached via the phases as predicted in the Gantt chart. Therefore, via this project that is DYNAMIC ANALYSIS OF PETROL ENGINE an experience regarding the designing of the engine and managing the vital details for making necessary modifications for improving the efficiency of the petrol engine are gained.


  1. http://en.wikipedia.org/wiki/History_of_the_internal_combustion_engine)
  2. http://en.wikipedia.org/wiki/Deflagration
  3. http://autoclub.rso.siuc.edu/frange.html
  4. http://autoclub.rso.siuc.edu/frange.html
  5. http://autoclub.rso.siuc.edu/frange.html
  6. http://autoclub.rso.siuc.edu/frange.html
  7. http://autoclub.rso.siuc.edu/frange.html
  8. http://www.kennedysdynotune.com/images/Camshaft3.jpg
  9. http://www.allproducts.com/manufacture100/shangdeautopart/product1.jpg
  10. http://www.metaldyne.com/metaldyne/images/sections/engine/products/connecting_rod_270.jpg
  11. http://www.tinindianperformance.com/images/forged_pontiac_crankshaft_b.jpg ).

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