1. Intake System: Air Induction and Volumetric Efficiency

2. Air Induction We will study how air and fuel are delivered into the cylinders. Objective of intake system  to deliver proper amount of air-fuel mixture (accurately, equally)  to deliver proper time Intake system consist of :  intake manifold, a throttle, intake valves, fuel injector/ carburetor

3. Volumetric Efficiency Volumetric efficiency in internal combustion engine is a ratio (or percentage) of what volume of fuel and air actually enters the cylinder during induction to the actual capacity of the cylinder under static conditions. Volumetric efficiency is affected by : i)Fuel ii)Mixture temperature iii)Valve overlap iv)Fluid friction losses v)Choked flow vi)Closing intake valve vii)Intake tuning viii)Exhaust residual ix)EGR

4. Volumetric Efficiency (Fuel) In naturally aspirated engines (no supercharging) the volumetric efficiency will always be less than 100% because fuel is added and the fuel vapour will displace incoming air. volumetric efficiency affected by type of fuel, how it is added and when it is added. The earlier the fuel is added in the intake system the lower the volumetric efficiency because more of the fuel evaporates before entering the cylinder. Multipoint injector is better to improve volumetric efficiency. In Diesels, GDI, fuel is added directly into the cylinder so get a higher efficiency. Gaseous fuels displace more incoming air than liquid fuels. Note: piston speed proportional to air flow velocity

5. V.E. (Intake Temperature) All intake systems are hotter than ambient air, so the density of the air entering the cylinder is lower than ambient air density. At lower speed, air remains in the intake system for longer time. So purposely heated to enhance fuel evaporation.

6. V.E. (Valve Overlap) #In engines valves don’t open and close instantaneously #In order to ensure that the valve is fully open during a stroke for volumetric efficiency, the valves are open for longer than 180 o. #The exhaust valve opens before BDC and closes after TDC and the intake valve opens before TDC and closes after BDC. #At TDC- period of valve overlap =both the intake and exhaust valves are open.Real time valve overlap is greater at low RPM. Volumetric efficiency getting lower at lower RPM.

7. VE (Friction Losses) The air flows through a duct through an air filter, throttle and intake valve Air moving through any flow passage or past a flow restriction undergoes a pressure drop. The pressure at the cylinder is thus lower than atmospheric pressure Greatest problem at higher engine speeds when the air flow velocity is high Solutions smooth walls avoidance sharp corners and bends no gasket protrusions multi intake valves

8. VE (Choked Flow) In choked flow the mass flow rate will not increase with a further decrease in the downstream pressure environment. Sonic velocity at some point in the system. Lowering volumetric efficiency at higher RPM.

9. VE (Closing Intake Valve) When the piston reaches BDC there is still a pressure difference across the intake valve and the mixture continues to flow into the cylinder, therefore the intake valve need to be close after BDC. Best time to close the intake valve is when the manifold and cylinder pressures are equal, close the valve too early and don’t get full load, too late and air flows back into the intake port. At high engine speeds, there are larger pressure drop across intake valve because of higher flow velocity, so ideally want to close valve later after BDC (60 o aBDC). At low engine speeds smaller pressure drop across the intake valve. Ideally it is better to close the intake valve earlier after BDC (40 o aBDC). Most engine cannot control the intake valve closes with the engine speed. The profile, or position and shape of the cam lobes on the shaft, is optimized for a certain engine revolutions per minute (RPM), and this tradeoff normally limits low- end torque, or high-end power.

10. VE (Intake Tuning) When the intake valve opens the air suddenly rushes into the cylinder and an expansion wave propagates back to the intake manifold at the local speed of sound relative to the flow velocity. When the expansion wave reaches the manifold it reflects back towards to intake valve as a compression wave. The time it takes for the round trip depends on the length of the runner and the flow velocity. If the timing is appropriate the compression wave arrives at the inlet at the end of the intake process raising the pressure above the nominal inlet pressure allowing more air to be injected. Many modern engines have passive constant-length intake runner systems. However, some advanced modern engine have active intake systems that can tune the manifold by changing the length of the intake runners to match the air flow rate at various engine operating conditions.

11. VE (Exhaust Residual) When the intake valve opens the cylinder pressure is at P e Part throttle (P i < P e ): residual gas flows into the intake port. During intake stroke the residual gas is first returned to the cylinder then fresh gas is introduced. Residual gas reduces part load performance. Supercharged (P i > P e ): fresh gas can flow out the exhaust valve

12. VE Improvement There are several standard ways to improve volumetric efficiency. A common approach for manufacturers is to use larger valves or multiple valves. Larger valves increase flow but weigh more. Multi-valve engines combine two or more smaller valves with areas greater than a single, large valve while having less weight. Carefully streamlining the ports increases flow capability. This is referred to as Porting and is done with the aid of an air flow bench for testing. Changing the diameter and length of intake manifold can improve VE. Variable valve timing, attempts to address changes in volumetric efficiency with changes in speed of the engine: at higher speeds the engine needs the valves open for a greater percentage of the cycle time to move the charge in and out of the engine. Volumetric efficiencies above 100% can be reached by using forced induction such as supercharging or turbocharging.

13. IAFM Runners diameter and length should equalize amount of air and fuel delivered to each cylinder. Large enough – no flow resistance Small enough – assure high air velocity and turbulence  enhance capability to carry fuel droplets, evaporates and air-fuel mixing. Some engine have active intake manifold. - Low speed  air is directed through longer, smaller diameter to keep the velocity high - High speed  shorter, larger diameter runners are used, minimize resistance but still enhance proper mixing To minimize resistance - runners must have no sharp bends - interior surface should be smooth

14. IAFM cont. 11 bhp = 0.75 kWh

15. VVT Variable valve timing, often abbreviated to VVT, is a generic term for an automobile piston engine technology. VVT allows the lift, duration or timing (some or all) of the intake or exhaust valves (or both) to be changed while the engine is in operation. The profile, or position and shape of the cam lobes on the shaft, is optimized for a certain engine revolutions per minute (RPM), and this tradeoff normally limits low-end torque, or high-end power. VVT allows the cam profile to change, which results in greater efficiency and power, over a wider rev-range.

16. VTEC VTEC (Variable Valve Timing and Lift Electronic Control) is a valvetrain system developed by Honda to improve the volumetric efficiency of a four-stroke internal combustion engine. This system uses two camshaft profiles and electronically selects between the profiles.

17. Mivec

18. VTC or VVT-i Variable valve timing allows the relationship between the separate inlet and exhaust camshafts to vary the valve timing overlap. A computer continuously vary the intake valve timing and overlap. The valve timing and overlap are adjusted through a series of simple mechanisms to ensure the optimum conditions apply across all the working rev range. The advantages are lower fuel consumption, lower exhaust emissions and higher power output. Because the system is continuously variable, an ‘i’ for ‘intelligent’ has been added to the acronym.

19. VVTL-i or i-VTEC Toyota’s VVTL-i is the most sophisticated VVT design yet. Its powerful functions include: Continuous cam-phasing variable valve timing 2-stage variable valve lift plus valve-opening duration Applied to both intake and exhaust valves The system could be seen as a combination of the existing VVT-i and Honda’s VTEC, although the mechanism for the variable lift is different from Honda.

20. D-4S or i-VTEC I Toyota's 2GR-FSE V6 uses a more advanced direct injection system, which combines both direct and indirect injection using two fuel injectors per cylinder, a traditional port fuel injector (low pressure) and a direct fuel injector (high pressure). This system known as D-4S or D4 Superior first appeared in the US with the launch of the Lexus IS 350.

21. Supercharger P atm P int > P atm A supercharger is an air compressor used for forced induction of an internal combustion engine. The greater mass flow-rate provides more oxygen to support combustion than would be available in a naturally-aspirated engine, which allows more fuel to be provided and more work to be done per cycle, increasing the power output of the engine. A supercharger can be powered mechanically by a belt, gear, shaft, or chain connected to the engine's crankshaft. Superchargers can spin at speeds as high as 50,000 to 65,000 rotations per minute (RPM). There are three types of superchargers: Roots, twin-screw and centrifugal. The main difference is how they move air to the intake manifold of the engine.

22. Supercharger Types The Roots supercharger is the oldest design As the meshing lobes spin, air trapped in the pockets between the lobes is carried between the fill side and the discharge side. Large quantities of air move into the intake manifold and "stack up" to create positive pressure. For this reason, Roots superchargers are really nothing more than air blowers. Least efficient supercharger for two reasons: They add more weight to the vehicle and they move air in discrete bursts instead of in a smooth and continuous flow.

23. Supercharger Types Twin-screw supercharger compresses the air inside the rotor housing. That's because the rotors have a conical taper, which means the air pockets decrease in size as air moves from the fill side to the discharge side. As the air pockets shrink, the air is squeezed into a smaller space. This makes twin-screw superchargers more efficient, but they cost more because the screw-type rotors require more precision in the manufacturing process.

24. Supercharger Types Centrifugal superchargers are the most efficient and the most common of all forced induction systems. They are small, lightweight and attach to the front of the engine instead of the top. Typically, a centrifugal supercharger will make it's maximum (quoted) boost at the engine's redline rpm and nearly nothing at 1500-2000 engine rpm. Boost builds exponentially with engine rpm, meaning that boost comes on very quickly in the upper half of the powerband. While this normally isn't a problem for lighter cars with manual trannsmissions, it poses a significant problem to heavier vehicles, towing vehicles, or vehicles with automatic transmissions.

25. Turbocharger A turbo can significantly boost an engine's horsepower without significantly increasing its weight In order to achieve this boost, the turbocharger uses the exhaust flow from the engine to spin a turbine, which in turn spins an air pump. The turbine in the turbocharger spins at speeds of up to 150,000 rotations per minute (rpm) One cause of the inefficiency comes from the fact that the power to spin the turbine is not free. Having a turbine in the exhaust flow increases the restriction in the exhaust. This means that on the exhaust stroke, the engine has to push against a higher back-pressure (turbo lag).

26. Super vs Turbo The key difference between a turbocharger and a supercharger is its power supply. Something has to supply the power to run the air compressor. In a supercharger, there is a belt that connects directly to the engine. It gets its power the same way that the water pump or alternator does. A turbocharger, on the other hand, gets its power from the exhaust stream. In theory, a turbocharger is more efficient because it is using the "wasted" energy in the exhaust stream for its power source. On the other hand, a turbocharger causes some amount of back pressure in the exhaust system and tends to provide less boost until the engine is running at higher RPMs. Superchargers are easier to install but tend to be more expensive.