Intake System.docx

Intake System As per Rule of Formula Bharat air intake to engine must pass through 20mm restrictor to limit the engine power and torque. Aim of this intake system is to optimise the air flow to restrictor and to maximize engine power and torque. Engine Specifications Made: KTM 390 Displacement: 373.3cc Clearance Volume: 22.5cc Compression Ratio: 12.88:1 Bore*Stroke: 89mm*60mm

(Intake System) This intake system consist of following * Venturi type restrictor * Plenum * Runner * Throttle body 1. Restrictor As per Formula Bharat rule the flow to engine must pass through a 20mm restriction. For Restriction there are two methods 1. By Orifice 2. By Venturi. While orifice has a lower coefficient of discharge than venturi , a venturi type restrictor is used.

Venturi is a tube with a convergent ,throat and divergent section based on Bernoulli’s law , the velocity of fluid will increase with decrease in area results in a decreased pressure. To optimise a venturi type restrictor we have to minimize the pressure difference between the inlet and outlet section of venturi, which depends on the angle of convergent and divergent section calculated by Reynolds Transport Theorem taking area as linear function with inlet and outlet diameter 28mm and throat diameter to solve and minimize the pressure difference between the inlet and outlet to get angle of convergent and divergent section to be 4 and 3 degree(half angle). 2. Runner To design a tuned runners for a low end torque Helmholtz’s Resonator model is used. Helmholtz’s model predict the resonant frequency of intake and engine hence increase in the volumetric efficiency. Resonance speed of engine is given by Nt = 955/K(a(A/lVeff)1/2) Where K = 2 for most of engines Veff = Vd/2 +Vc (cm3) A = Area of cross section of Runner(cm2) L = Runner length Gives a runner length as follow RPM Runner length (cm)

2500 19.15 (16th harmonic)

5000 19.5(2nd harmonic)

7000 19.55(2nd harmonic)

10000 19.15(1st harmonic)

So the effective runner length was chosen to 19.5 cm An elliptical Bellmouth was also used at runner opening to increase the coefficient of discharge. 3. Plenum Volume To calculate the plenum volume “Emptying and Filling Model” of Plenum was used. According to this model the average time to fill the volume by restrictor must be equal to time taken to emptying the volume by engine. Assuming that at any given time pressure of manifold is uniform. The continuity equation can be given as dma,m/dt = mventuri – mcyl mventuri = mass flow rate through the venturi mcyl = mass flow rate in cylinder ma,m = mass flow in manifold/ plenum Can be written as dpm/dt + nv VdN/2Vm = mventuri R Tm/Vm

Solving for minimum pressure of manifold for maximum flow through venturi gives Vm/Vd approximately equal 8. So for final plenum volume was chosen to 9 times the Vd so that plenum has always air left for engine. Gives a plenum volume approx. 3l. Throttle Body:- for a throttle body with greater cross section area than the throat the flow will choke at throat for a smaller angle of throttle make the rest of angle of throttle unusable. It is hard to get a smaller throttle body (28mm dia.) of a fuel injected bike. So we designed the throttle body as per our requirement. the throttle body is actuated by butterfly valve mechanism and retains place for stock TPS and IACV. Bore = 28mm Length = 3.5cm Resulting T/B have 230gms of weight.