1Korea University of Technology and Education

 Intake manifold  It is a system designed to deliver air to the engine through pipes to each cylinder.  The length of a runners and its diameter should be sized together to equalize. 2Korea University of Technology and Education

 VIS(variable induction system) 3Korea University of Technology and Education

 VIS(variable induction system)  Low speed  High speed 4Korea University of Technology and Education

 Volumetric efficiency  It is desirable to have max. volumetric efficiency in the intake of any engine. This will vary with engine speed. 5Korea University of Technology and Education

 Fuel  The type of fuel, as well as how and when it is added, will determine how much the volumetric efficiency is affected.  Multipoint injectors, which add fuel at the intake valve ports, will have better efficiency  Gases fuels  The later that fuel vaporizes in the intake system, the better is the volumetric efficiency.  On the other hand, the earlier that fuel vaporizes, the better mixing process. 6Korea University of Technology and Education

 Heat transfer  At lower engine speeds, the air flow rate is slower and the air remains in the intake system for a longer time. It thus gets heated to higher temp at low speeds, which lowers the vol efficiency curve in Fig.5-1 at the low-speed end. 7Korea University of Technology and Education

 Valve overlap  During the period of valve overlap, the exhaust gets carried back into the cylinder and lowering the vol efficiency.  This problem is greatest at low engine speeds.  This effect lowers the efficiency curve in Fig.5-1 at the low engine speed end. 8Korea University of Technology and Education

 Fluid friction losses  The viscous flow friction results in decreasing the efficiency on the high-speed end of the curve in Fig.5-1.  To reduce this restriction, the intake valve flow area has been increased by building multi-valve engines having two or even three intake valves per cylinder. 9Korea University of Technology and Education

 Choked flow  As air flow is increased to higher velocities, it eventually reaches sonic velocity. This is choked flow.  The result of this is a lowering of the efficiency curve on the high-speed end in Fig Korea University of Technology and Education

 Closing intake valve after BDC  The pressure differential still exists the instant the piston reaches BDC and air is still entering the cylinder. This is why the closing of the intake valve is timed to occur aBDC.  Until the air is compressed to a pressure equal to the pressure in the intake manifold, air continues to enter the cylinder.  This valve-closing point in the engine cycle is highly dependent on engine speed 11Korea University of Technology and Education

 Intake Tuning  When gas flows in a pulsed manner, as in the intake manifold of an engine, pressure waves are created the travel down of the length of the flow passage.  If the length of the intake manifold runner and the flow rate are such that the pressure waves reinforce at the point where the air enter the cylinder through the intake valve, the pressure pushing the air in will be slightly high, and slightly more air will enter the cylinder.  When this happens, the system is tuned. 12Korea University of Technology and Education

 Exhaust Residual  During the exhaust stroke, not all of the exhaust gases get pushed out of the cylinder by the piston, a small residual being trapped in the clearance volume  When the very hot gas mixes with the incoming air, it heats the air, lowers the air density, and decreases volumetric efficiency. 13Korea University of Technology and Education

 EGR  In all modern automobile engines and in many other engines, some exhaust gas is recycled(EGR) into the intake system to dilute the incoming air.  This reduces combustion temperature in the engine, which results in less nitrogen oxides in the exhaust.  Not only does this exhaust gas displace some incoming air, but it also heats the incoming air and lowers its density. 14Korea University of Technology and Education

 Intake valve  Intake valve of most IC engine are poppet valves and are spring loaded closed and pushed open at the proper cycle time by the engine camshaft  Most valves and valve seats against which they close are made of hard alloy steel or, in some rarer cases, ceramic.  The distance that a valve opens is called valve lift and is generally on the order of a few millimeters to more than a centimeter, depending on the size. The valve lift is usually about 5 to 10 mm for automobile engines. 15Korea University of Technology and Education

 Intake valve  l max < d v /4  l max : valve lift when the valve is fully open  d v : diameter of valve  Fig Korea University of Technology and Education

 Fig. 5-4  Ex. Problem Korea University of Technology and Education

 Variable valve control  The variable valve control systems allow for more efficient engine operation by varying at which valves open, duration of opening, and valve overlap period. 18Korea University of Technology and Education

 Variable valve control  VVC(variable valve control), VVA(variable valve actuation), VVE(variable valve event), VVS (variable valve system), VTC (variable timing control) 19Korea University of Technology and Education

 Variable valve control  Since the late 1990s, engines with VVC have used several methods to obtain this goal. Most of these earlier systems worked only on the intake valves and had no lift variation.  The most modern of systems can now control both intake and exhaust valves, timing and lift.  The most modern system of VVC have no camshaft and use electrical solenoids to open and close valves directly, or through an electro- mechanical or electro-hydraulic connection. 20Korea University of Technology and Education

 Fuel Injectors  Fuel injectors are nozzles that inject a spray of fuel into the intake air.  They are normally controlled electronically, but mechanically controlled injectors, which are cam operated.  At the proper time, the nozzle is opened and fuel is sprayed into the surrounding air.  The amount of fuel injected each cycle is controlled by injector pressure and time duration of injection. 21Korea University of Technology and Education

 Fuel Injectors  An electronic fuel injector consists of the following basic components: valve housing, magnetic plunger, solenoid coil, helical spring, fuel manifold, and pintle(needle valve).  Each valve can have one or several orifice opening, each having a diameter of about 0.2 to 1.0 mm.  In mechanically controlled injector there is no solenoid coil, and the plunger is moves by the action of a camshaft. 22Korea University of Technology and Education

 Fuel Injectors 23Korea University of Technology and Education

 Common rail  Some systems have a single fuel pump(common rail) supplying the injectors of all cylinder or a bank of cylinders.  The fuel can be supplied at high pressure with the injectors acting only as a metering device.  CRDi system of the 4 th generation has the about 180 MPa injection pressure. 24Korea University of Technology and Education

25Korea University of Technology and Education

 Injection Pressure  Only moderate injector pressure is required for SI engines using port injectors or throttle body injectors (e.g., kPa absolute)  Injectors used for injecting directly into the combustion chamber(DI) operate at much higher pressures, up to 10 MPa.  Many SI engine direct injection system that use gasoline (GDI) inject a combination of fuel and air. 26Korea University of Technology and Education

27Korea University of Technology and Education

 Multipoint Port Injection Systems  Most modern automobile SI engines have multipoint port fuel injectors.  In this type of system, one or more injectors are mounted by the intake valve of each cylinder.  Each cylinder has its own injector or set of injectors which give a fairly constant fuel input cycle-to-cycle and cylinder-to-cylinder.  Multipoint port injector system are better than carburetors or throttle body injector systems at giving consistent AF delivery.  Intake system with multipoint injectors can be built with improved volumetric efficiency. 28Korea University of Technology and Education

 Direct Injection System for SI engines  Engines that use gasoline direct injection(GDI ) generally operate in three different modes.  At light load and part throttle, the engine will operate with a stratified charge mode and an overall AF of about 50:1  At medium load, it will still operate with stratified charge, but with an AF of about 20:1.  At high load or WOT operation, fuel is injected only during the intake stroke and max. thermal efficiency is obtained by operating with a homogeneous stoichiometric air-fuel mixture. 29Korea University of Technology and Education

30Korea University of Technology and Education

 Supercharger  Superchargers and turbochargers are compressors mounted in the intake system and used to raise the pressure of the incoming air.  This added air and fuel creates more power  Superchargers are mechanically driven directly off the engine crankshaft.  Disadvantages : parasitic load, higher cost, greater weight, and noise  Advantages : quick response 31Korea University of Technology and Education

32Korea University of Technology and Education

 Turbocharger  The compressor of a turbocharger is powered by a turbine mounted in the exhaust flow of an engine.  The advantage of this is that none of engine shaft output is used to drive the compressor, and only waste energy in the exhaust is used.  A disadvantage of turbochargers is turbo lag, which occurs with a sudden throttle change. When the throttle is quickly opened to accelerate an automobile, the turbocharger will not response quite as quickly as a supercharger. 33Korea University of Technology and Education

34Korea University of Technology and Education

 Dual-Fuel Engines  In some third-world countries dual-fuel engines are used because of the high cost of diesel oil.  Large CI engines are run on a combination of natural gas and diesel oil. Natural gas is the main fuel because it is more cheaply available. However, natural gas is not a good CI fuel by itself because it does not ready self-ignite (due to its high octane number) 35Korea University of Technology and Education

 Two Stroke Engine  Inlet air in two-stroke cycle engines must be input at a pressure greater than atmospheric.  Following blowdown, at the start of the intake process, the cylinder is still filled with exhaust gas at a atmospheric pressure.  Air under pressure enters the cylinder and pushes most of the remaining exhaust residual out the still-open exhaust port. This is called scavenging. 36Korea University of Technology and Education

 Scavenging ways  Cross scavenging  Loop scavenging  Uniflow scavenging 37Korea University of Technology and Education

 CI engines  CI engines are operated unthrottled, with engine speed and power controlled by the amount of fuel injected during each cycle. This allows for high volumetric efficiency at all speed.  Fuel is added late in the compression stroke, starting around 20 o bTDC.  Injectors mounted in the head inject directly into the combustion chamber. 38Korea University of Technology and Education

 CI engines  Injection pressure of 20 to 200 MPa are common. A typical engine could have injection pressure of 25 MPa at idle, 135 MPa at nominal speed, and 160 MPa at high speed. 39Korea University of Technology and Education

40Korea University of Technology and Education