PART1 (a) Internal Gas Flows
Anairflow bench testis a process used for testing the aerodynamic properties o fan enginecomponent. It is related to or less similar to the wind tunnel, andit uses an air flow bench. This air flow-bench makes it possible totest inlet manifolds, valve profiles, exhaust systems, air cleaners,etc. (Vizard, 2012, p.12). The main objective of flow bench testingis finding the actual airflow figures by circulating air undercontrolled conditions. With this, it is possible to study airflowcharacteristics such as velocity, turbulence, tumble, swirl, anddistribution
ThePrinciple of Flow Bench Test
Aflow bench is made up of an air pump, means of metering, Instrumentsfor measuring pressure and temperature such as manometers, andseveral controls. The test piece is placed on the surface and somepressure, usually called test pressure applied, from which theresulting airflow is measured. Pressure drops across an orifice witha known characteristic determine the air flow rate (Gilles, 2011,p.23). Greater air flow rate causes a greater pressure drop. Watercolumn manometer measures the flow rate while the test pressure. Theprocess does not depend on the conditions of the atmosphere such asair temperature and pressure. Various parameters are varied on thetest piece and the corresponding measurements taken. For a fullrange of accurate testing, several orifices are used.
Theapparatus used in this test include Air flow box, Vertical andInclined Manometers, Orificeholes and a bench
Carryingout a Test
Inthe Flow bench, air flows via the engine cylinder head to flow benchset up. This air passes in an air pump exiting via the vents on theflow bench sides. This air flow measurement is in Cubic foot perminute (CFM).The pressure is the difference that occurs over an adjustable airflow orifice mounted on the flow bench (Gilles, 2011, p.31). Severalranges are taken using a flow meter to achieve high accuracy over. Inthe bench, it is possible to vary full-scale flow measurement from 25CFM to 1000 CFM.
CylinderAdaptors mount the cylinder heads to the air flow bench. The adaptorsare made of the 4-inch long tubes and have the same bore as that ofthe engine. The tubes have a flange on each of the ends. The lowerflange fixes on the flow tester while the upper one is mounts on theengine cylinder head. There are gaskets between the flanges to makethe union air tight. It is sometimes convenient to make the adaptorflange 20% wider than the test cylinder. It ensures that the there issupport for the head when it is offset to check the end cylinders(Vizard, 2012, p.31).
Toachieve various valves test positions desired, a threaded mount isattached to a rocker arm stud. It makes the end of the bolt is incontact with the end of the valve stem. On the cylinder head intakeside, a curved entrance guide is installed so that it leads the airinto to the head. This guide has a thickness equivalent to one portwidth. An alternative to this is the intake manifold (Gilles, 2011,p. 33).
Resultsof a Bench Test
Thevolume of air flowing through the port in a given time is measuredusing cubic feet per minute (CFM) or sometimes cubic meters persecond. Valve lift is expressed as an actual dimension in decimalinches or mm. The lift is also expressed as a ratio between acharacteristic diameter and the lift Length/Depth.In most cases, engines have a Length/DepthRatio of 0 to 0.35. For instance, a valve of1-inch-diameter wouldlift to a maximum of 0.35 inch. When carrying out the testing,the valve is set at Length/Depthsratios, from0.05 to 0.3 and the corresponding readings notedsuccessively (Vizard, 2012, p.16). From this, it is possible tocompare the efficiencies of the intake ports with other sizes of thevalve, because the valve lift is proportional rather than complete.For evaluation with tests by others, the original diameter used todetermine lift must be the same.
Calculationof Air flow: V (m/s) = L * N/30000 * (D /d)2
Presentingthe results graphically
Fig.1 Graph of Air Flow Vs RPM
Thereare three types of metering elements that flow benches can use. Theseare an orifice plate, Venturi meter, and pitot/static tube. All ofthese achieve similar accuracy. Most industrial machines make use oforifice plates because they are simple in construction, and theyeasily provide multiple flow ranges. The Venturi offers somesubstantial improvements in metering efficiency, but its cost isquite high.
Airflow bench is one of the basic high-performance tools that enginedesigners and builders should have.
Commenton Differing Valve Seat Angles
Multiplevalve angles and fully curved valve seats achieve good airflow. Atypical competition intake valve seat will consist of a 30° top cut100" wide, a 450seat, 40" wide, and a 70° inside cut 180" wide. An exhaustvalve will blend well with a 15° top cut 60" wide, followed bya 45° seat 60" wide, and a 75° inside cut 100" wide. TheFlow-bench test will in most cases reveal a superior shape for anyspecified head (Shi, Ge& Reitz, 2011).
PART1 (b) Literature Review
Oneway of optimizing the power of an engine is by increasing thepressure, and hence force applied on the piston, during the powerstroke. The amount of work that the power stroke delivers depends onthe air-fuel mixture inside the combustion chamber. The combustion atthe end of the compression stroke and during the power stroke dependson how much air mixes with the fuel. Compressing the air increasesits density but its volume decreases. Compressing air at thebeginning of an engine cycle, therefore, increases the power outputby increasing the volume of air that is mixed with the fuel. This isbecause the total volume of the space occupied in the cylinderdecreases when compressing air and more air is used to burn the fuel.
Theprocess described above is achieved by superchargers andturbochargers. They increase the pressure hence the density of theair, increasing the power developed by the engine. The most commonsuper-chargers are mechanical superchargers. The supercharger has acompressor that is driven using power from the engine. Aturbocharger, on the other hand, is a combination of a compressor anda turbine. These mechanisms require the use of another shaft.However, they do not use the engine power to provide the workrequired to run the compressor. The exhaust gasses run the turbines,which uses their energy content to drive the shaft that runs thecompressor.
Anothermethod of obtaining optimum engine power output is by improving thecapacity of airflow in the engine or improving the burning efficiencyof the air-fuel charge. Most engine manufacturers focus primarily onincreasing the airflow (Ganesan, 2012, p.41). The carburetor’s flowresistance, intake manifold, and cylinder head are reduced to ensurethat there is more air passing through the engine. As a result, thereare many after-market carburetors, intake manifolds, and cylinderheads that are ported out and all are designed to increase airflowthrough the engine.
Thevolumetric efficiency of the engine, swirl ratio and characteristicsof combustion depend on the geometry of the intake port (Ferguson&Kirkpatrick, 2015, p.32). Studies have been carried on a differentconfiguration of the port that gives optimal swirl ratio useful forvarious engine applications and conditions of operation and henceoptimal combustion.
Themain function of the air supply system is to deliver the correctamount of clean air to the engine that is required for burning in themanifold chamber. The efficiency of air flow in the air intake systemdirectly affects the power produced by the engine. The key task of anintake port is to supply air equally to the cylinders. The equalsupply of air to cylinders is very critical for the optimal operationof the engine (Gupta, 2013, p.22). Uneven distribution of air to thecylinders leads to non-uniform volumetric efficiency in cylinders,loss in power and increased fuel intake. When an Internal Combustionengine is running, pressure waves occur because of pressure drop incylinders in intake strokes.
Thereis high turbulence in the cylinders during the intake stroke. Theturbulence then drops as the flow rate declines towards the engine’sbottom dead center. The turbulence increases again during thecompression stroke. During this time, swirl, squish, and tumbleincrease towards the engine’s top dead center (Gupta, 2013, p.20).The increased turbulence at the top during starting is highlyimportant for the process of combustion in the engine. It breaks andspreads the burning flame front very fast compared to a laminarflame. The air-fuel mixture is completely burned within a fraction ofthe time, avoiding self- igniting and knocking. To increase theturbulence, engine cylinder is designed to expand during thecombustion process.
Inthe design and development of the engines, it is important to ensureoptimal as flow through intake ports. Optimum gas flow ensures thatthe movement of air-fuel charge produced during the intake flow has aconsiderable effect on the quality of air-fuel mixture and theburning process. The patterns of the flow fields in the combustionchamber when the fuel is injected, and the resulting interactionswith the jets of the fuel, and combustion process are dominantelements of the engine performance and determine the levels ofexhaust emissions in the engine.
Theliterature reviewed has shown that the designing of the inletmanifold arrangement is very significant in an internal combustionengine (IC). The Horsepower of an IC engine varies proportionally tothe quantity of air drawn into the cylinder and retained untilignition takes place. By reducing the resistance of the air flowingthrough the intakes and exhaust tract, the filling of the cylinderimproves and, therefore the engine power increases proportionally.
Optimumengine power output is achieved by improving the capacity of airflowof the engine and improving the burning efficiency of the air-fuelcharge. One of the ways of achieving this is by reducing the flowresistance in the carburetor, air intake manifold, and cylinder headto ensure that there is more air passing through the engine. Enginemanufacturers should, therefore, optimize the gas inflow throughintake ports because the movement of charge produced by the intakeflow considerably affects the quality of air-fuel mixture andcombustion. Other important factors to consider in optimal enginedesign include the exact matching of the engine, parameters of fuelinjection, the shape of the bowl, compression ratio, andcharacteristics of scavenging and recirculation of exhaust gas(Agrawal, 2006, p.41).
Designersand manufacturers of engines should also consider the following. Achange in direction of flow such as bends and expansion causes a lossin flow and decreases air velocity. The Port area should range from65% to 100% of the valve area. Materials are primarily removed fromthe outside of port bends and not in the inside. By doing this, theflow improves by increasing the radius of the bend. Port length andsurface finish do not affect the flow. The valve seat shapesubstantially affects the flow (Agrawal, 2006).
SECTION2: Chassis Analytical design
Calculationof Various Force Components
=DragxVelocity = 9.07KNM/s (KW)
=Dragx Height of CoG = 77.55Nm @33.33m/s
Toobtain weight, mass is multiplied by the gravitational acceleration(W = mg). Because the weight is being pulled towards the core of theearth by the force of gravity, it is regarded as force and thereforemeasured in Newton (N)
TotalWeight, WT= 1,519.4 x 9.81 =14,905.31N
FrontWeight, WF= 14,905.31 x 40/100 = 5,962.13N
RearWeight WR= 14,905.31 x 60/100 = 8943.19N
Takingmoments about the front:
WF.0 +WT. a – WR. LWB = 0
Toobtain equilibrium state, the sum of all moments is equal to zero.
Therefore,WT.a = WR.LWB
Thisgives a= WR.LWB/WT =1.389m
Andb = LWB– a =0.932m
Calculationof Front Forces with 40% load
Sideforce = 10.53×40/100 =4.21Nm
Pitchingmoment = 81.28×40/100 =32.51Nm
Rollingmoment = 40.64×40/100 =16.26Nm
Yawingmoment = 365.75×40/100 =146.30Nm.
Calculationof Rear forces with 60% Load
Sideforce = 10.53×60/100 =6.32Nm
Pitchingmoment = 81.28×60/100 =48.77Nm
Rollingmoment = 40.64×60/100 =24.38Nm
Yawingmoment = 365.75×60/100 =219.45N
Applicationin Design of Chassis
InAutomotive aerodynamics, drag force consists primarily of two forces.One is theFrontal pressure that resultsfrom the air when it flows on the front of the vehicle.Another component is the Rear vacuum, which occursas a result of an apparent hole created in the air as the vehiclepasses through it. The vacuum results from the fact that the airmolecules do not close the hole as quickly as the vehicle makes.Because of this vacuum, there is a sucking effect on the oppositedirection. Drag foIt is because the force that results from thevacuum is much more than that created by frontal pressure. Using thisknowledge, it is possible to optimize the whole length of the chassisto ensure there are minimum turbulence and maximum speed.
Pitch,Yaw and Roll Moments
TheRoll, pitch and yaw refer to the rotations that occur about the x, yand z-axes, starting from a steady and a defined equilibrium state.Conventionally, the rolling moment acts about the longitudinal axisthe yaw moment acts about the vertical body axis while the Pitchmoment acts around an axis that is vertical to the longitudinalsymmetry of the vehicle (Genta & Morello, 2008).
InAutomotive industry, designers use these moments to build controlmechanisms for the orientation of the vehicle about its center ofmass. In a proper design, these mechanisms of control apply forces insome of the directions and produce moments about the aerodynamiccenter of the vehicle. The vehicle, therefore, can rotate in pitch,roll, or yaw. For instance, a pitch moment is a vertical force thatacts at a distance forward or backward from the aerodynamic center ofthe vehicle. The vehicle thus to pitches up or down. The knowledgeof these forces (Roll, Pitch, and Yaw moments) is, therefore,important to vehicle designers because it helps attain vehiclestability in the design (Genta & Morello, 2008).
Agrawal,S. K. (2006). Internalcombustion engines.New Delhi: New Age International (P) Ltd. Publishers.
Ferguson,C. R., & Kirkpatrick, A. (2015). Internalcombustion engines: Applied them sciences.
Ganesan,V. (2012). ICengines.New Delhi: Tata McGraw-Hill.
Genta,G., & Morello, L. (2008). Theautomotive chassis: Vol. 1.Dordrecht: Springer.
Gilles,T. (2011). AutomotiveEngines: Diagnosis, Repair, and Rebuilding.Clifton Park, NY: Delmar/Cengage Learning.
Gupta,H. N. (2013). Fundamentalsof internal combustion engine.Delhi: PHI Learning.
Ling,F. F., Genta, G., & Morello, L. (2009). TheAutomotive Chassis: Vol. 2: System Design.Dordrecht: Springer Netherlands
Vizard,D. (2012). DavidVizard`s how to port & flow test cylinder heads.North Branch, MN: CarTech.