INTAKE RESTRICTOR1. Objectives of this research is to optimize a venturi type design to allow maximum possible mass flow rate to the engine from 20 mm restrictor buy reducing the difference in pressure across venturi at all speeds.2. Analytical calculations are done based on standard results to get maximum mass flow rate and CFD tool is used to calculate minimum pressure drop across the restrictor buy varying converging and diverging angles of venturi.3. The aims therefore are Maximum Mass Flow Rate with Minimum Pressure Drop.4. At high engine speeds, engine requires much more air for combustion and thus mass flow rate should increase, but due to restrictor area being less air has to pass with very high velocity to compensate or fill the engine with required amount of air.5. Thus air tries to achieve maximum velocity through restrictor which gives rise to critical flow conditions, where in air reaches its maximum speed of Mach 1 at the restrictor.6. In a nozzle or other constriction, the discharge coefficient (also known as coefficient of discharge) is the ratio of the actual discharge to the theoretical discharge, i.e., the ratio of the mass flow rate at the discharge end of the nozzle to that of an ideal nozzle which expands an identical working fluid from the same initial conditions to the same exit pressures.7. With some basic calculations for throttle body diameter for an engine with 600 cc of displacement and for revolutions per minute of 13000, the diameter of throttle body comes out to be 38 mm, and the same is widely used in competition. This dimension will be the diameter of venturi at inlet and outlet.8. We have two dimensions which are fixed, so we have two dimensions on which the venturi will perform and these are converging diverging angles and length of venturi. Thus we have defined two known and two unknown physical parameters for design of venturi.9. We also know that temperature at inlet is ambient and pressure at inlet is atmospheric.10. For boundary conditions at outlet of venturi we can have either pressure, velocity or mass flow rate. Calculating pressure and velocity at outlet of venturi involves complex procedures and thus gives rise to some errors. Mass flow rate at outlet can be easily calculated by using choked flow equation.11. Mass Flow Rate is maximum when M=1.At these conditions flow is choked.12. The most important parameter in compressible flows is Mach number Ma=V/C where V is flow velocity and C is speed of sound. If Mach number is less than 0.3, compressibility effects can be neglected as there is around 3 % change in density. Whereas if Mach number is from 0.3 to 1 flow is called subsonic and if Ma>1 flow is supersonic, in this regions compressibility increases and its effects are considerable.13. A venturi in itself can allow a maximum of 0.0703 kg/s of air flow to engine, considering no losses in friction and turbulence. the aim is to allow the engine to achieve the maximum mass flow with minimal pull from the engine.14. The optimum solution to achieve maximum possible mass flow rate of air as quickly as possible is to minimize the pressure loss through the flow restriction device.Different CFD Analysis were made for different converging and diverging angles. The one with the least pressure drop was selected. 15. In many documented studies and literature, the recommended shape for the convergent part of the restrictor is an elliptical curve leading to the minimum diameter point, while a 3 to 7 taper on the divergent end of the restrictor would allow the air to regain the pressure lost as air flows into the constriction16. The phenomenon of a choked flow system is one pertaining to compressible flow, such as that of air in the atmospheric environment flowing through the air intake system, and into the engines cylinders. In the FSAE context, the main location in which choked flow is likely to develop would be at the air intake restrictor. It is formed when air flows across a path with a decreasing cross-sectional area.

INTAKE RUNNERS

17. The intake runners are the parts of the air intake system which delivers air from the intake manifold to the cylinders (see Figure 3). In each runner, the dominant phenomenon that governs its performance is actually the effect of acoustic waves.18. 19. The objective of a tuned intake runner would be to manipulate this reflected wave (while the engine is running at a desired RPM) to make sure that a high-pressure region coincides with a subsequent Valve opening, improving air-flow into the cylinder, improving volumetric efficiency, hence achieving peak torque at the required RPM.20. The calculation for the length of the tuned intake runners is based upon the duration between two events of the intake valves operation: the first being the closing of the intake valve, and the second being the re-opening of the intake valve on the next cycle.21. While the tuning of runner lengths give the engine the capacity to improve its volumetric efficiency by timing a higher-pressure air column into the cylinder when the intake valves open, it would be necessary to note that the length of the runner is only tuned for a particular RPM, and that at other RPMs, particularly those at which the reflected waves position a lower-pressured air column at the intake valves as it open, will suffer a decrease in volumetric efficiencies as a result.22. RunnerLength= ((EVCD 0.25 V 2) (rpm RV)) - DEVCD=Effective Valve Close DurationReflective Value-RV ReflectiveValueisthereflectedwave(1,2,3,n)V-Pressure Wave Speed

http://auto.howstuffworks.com/question517.htm (How do tuned Intake Runners Work On your Car)23. http://www.rbracing-rsr.com/runnertorquecalc.html (Peak Torque And Runner Dimensions Calculator)24. In general a longer runner is used to maximize low speed torque and larger runner is used to maximize high speed torque.

PLENUM DESIGN1. Some relatively common practices in performance air systems are the use of baffles to change the effective length of the runner and moving internals to change the effective volume of the plenum at different rpms.2. Many papers suggest that the plenum chamber should be 1 to 4 times as large as the engine displacement. However, there are sometrade-offsto consider. If the plenum is too small, the restrictor could end up choking flow, which would result in a significant loss of power. If the plenum is too large, there is a decrease in throttle response, which is very important for a race car3. Large Plenums can often compensate for the restrictor since the air comes from the plenum resulting in greater volumetric efficiency and thus greater power.4.