MIXTURE FORMATION IN SPARK IGNITION ENGINES Chapter 5
Mixture formation in SI engine Engine induction and fuel system must prepare a fuel-air mixture that satisfiesthe requirements of the engine over its entire operating regime The constraints of emissions may dictate a different air fuel ratio and also require recycling some exhaust gas. (EGR) Relative proportions of fuel and air that give the above requirements depend on engine speed and load. Optimum air-fuel ratio for SI engine is that which gives 1. Required power output 2. Lowest fuel consumption 3. Consistent with smooth and reliable operation
Air induction systems
SI engine fuel supply system
Functional requirement of fuel supply system The functional objectives for fuel injection systems can vary, beside the central task of supplying fuel to the combustion process There are several competing objectives such as: Power output Fuel efficiency Emissions performance Ability to accommodate alternative fuels Reliability Driveability and smooth operation Initial cost Maintenance cost Diagnostic capability Range of environmental operation Engine tuning
Mixture formation in SI engine There are three mixture formation techniques exist for gasoline engines I. Carburetor II. Port fuel injection - inject the fuel into the intake manifold Depending the position of the injector a. Single point injection b. Multipoint injection III. Direct injection - inject the fuel directly into the cylinder The primary difference between carburetors and fuel injection is that fuel injection atomizes the fuel by forcibly pumping it through a small nozzle under high pressure
Mixture formation in SI engine
Mixture formation in SI engine - Carburetor The process of formation of a combustible fuel-air mixture by mixing the proper amount of fuel with air before admission to engine cylinder is called carburetion and the device which does this job is called a carburetor.
Mixture formation in SI engine - Carburetor The process of carburetion is influenced by The velocity of incoming air The velocity of the air stream at the point where the fuel is injected has to be increased. This is achieved by introducing a venturi section in the path of the air. The vaporization characteristics of the fuel Will require a volatile fuel for quick evaporation and mixing with air The temperature of the incoming air and Higher atmospheric air temperature increases the vaporization of fuel and produces a more homogeneous mixture. The design of the carburetor Proper design of carburetor elements alone ensures the supply of desired composition of the mixture under different operating conditions of the engine.
Mixture formation in SI engine - PFI The point or location of fuel injection is one way to classify a gasoline injection system. A single-point injection system, also called throttle body injection (TBI), has the injector nozzles in a throttle body assembly on top of the engine. Fuel is sprayed into the top center of the intake manifold.
Mixture formation in SI engine - PFI A multi-point injection system, also called port injection, has an injector in the port (air-fuel passage) going to each cylinder. Gasoline is sprayed into each intake port and toward each intake valve.
Mixture formation in SI engine - PFI
Mixture formation in SI engine - PFI Electronic control unit (ECU) is a generic term for any embedded system that controls one or more of the electrical systems or subsystems in a motor vehicle. An engine control unit (ECU) is a type of electronic control unit that determines the amount of fuel, ignition timing and other parameters an internal combustion engine needs to keep running. It does this by reading values from multidimensional maps which contain values calculated by sensor devices monitoring the engine.
Mixture formation in SI engine-pfi Most port injection today occurs with the intake valve closed Evaporation and mixture formation outside the cylinder prevents large droplets from directly entering the combustion chamber large drops enter the cylinder, may be deposited on the walls, due to the low pressure and density of the gas, and increase HC emissions.
Mixture formation in SI engine - PFI The classical gasoline injector today is the solenoid injector The majority of injectors used these days are low-and mediumpressure injectors with injection pressures in the range of 0.5 to 1.5 MPa
Mixture formation in SI engine - PFI The injectors can survive the excessive temperature and pressure of combustion by using the fuel that passes through it as a coolant The electronic fuel injector is normally closed, and opens to inject pressurized fuel as long as electricity is applied to the injector's solenoid coil. When the injector is turned on, it opens, spraying atomized fuel at the combustion chamber. Depending on engine operating condition,injection quantity will vary.
Mixture formation in SI engine - PFI Injectors for port fuel injection differ mainly in the type of nozzle used to generate the desired spray shape The pintle-type injector produces a cone-shaped spray, the single-hole injector a pencil-shaped spray, and the multi hole plate injector produces multiple sprays according to the number of holes
Mixture formation in SI engine - DFI Compared to the conventional diesel injection near top dead center, the direct injection of gasoline may occur already during the induction stroke in the case of homogeneous mixture formation (full load), or very late during the compression stroke in the case of stratified charge operation (part load)
Mixture formation in SI engine -DFI
Mixture formation in SI engine -DFI Among other techniques like cylinder cutoff or the application of variable valve trains the direct injection of gasoline is the measure with the highest potential to reduce fuel consumption and thus also CO2-emissions Compared to a similar PFI engine, about 15 25% reduction of fuel consumption at part load are theoretically possible Depending on the operating point of the engine, the direct injection of gasoline offers different advantages compared to the PFI technique.
Mixture formation in SI engine -DFI
Mixture formation in SI engine
Mixture formation in SI engine -DFI
Mixture formation in SI engine-dfi
Mixture formation in SI engine-dfi
Mixture formation in SI engine-dfi
Mixture formation in SI engine-dfi
Mixture formation in SI engine-dfi
Mixture formation in SI engine-dif
Mixture formation in SI engine-dfi
Mixture formation in SI engine-disc
Mixture formation in SI engine-disc
Mixture formation in SI engine-disc
Mixture formation in SI engine-disc
Mixture formation in SI engine
Mixture formation in SI engine
Mixture formation in SI engine
Mixture formation in SI engine-dfi
Mixture formation in SI engine-mm
Mixture formation in SI engine-mm
Mixture formation in SI engine-mm
Mixture formation in SI engine
Mixture formation in SI engine
Mixture formation in SI engine
Mixture formation in SI engine