Fuel Injection System ME 432 ICE 2 Carburetors and Fuel Injectors 3 Why Fuel Injectors for SI Engines • Fuel distribution through carburetor 4 Why Fuel Injectors for SI Engines • To improve the distribution of air-fuel ratio (fuel richness) in all cylinders of multi-cylinder engines • To improve the breathing capacity i.e. volumetric efficiency • To reduce or eliminate detonation • To prevent fuel loss during scavenging in case of two-stroke engines 5 Fuel Injection System – Advantages • Improved Atomization • Better Fuel Flow • Smoother Idle • Improved Fuel economy • Low Emissions • Better cold weather drivability • Increased engine power 6 Types of Injection Systems • Manifold Injection (Throttle Body Injection) • Port Injection (Multi Point Fuel Injection) ▫ Continuous ▫ Timed • Gasoline Direct Injection (GDI) 7 Single-Point/Throttle Body Fuel Injection • One or two injectors mounted inside the throttle body • Fuel sprays directed to center of intake manifold 8 Single-Point/Throttle Body Injection 9 Port or Multi Point Fuel Injection • MPFI 10 Multi-Point Port Injection • Injector located in each branch of inlet manifold, Air in below throttle valve. • Injectors spray fuel directly Throttle valve Injector into each port. Fuel in • Engine Control Unit (ECU) controls opening of injectors (in case of EFI) Inlet manifold 11 Continuous Injection System • Pressure driven fuel system 0.75-2.0 bar • Fuel injected immediate downstream of throttle plate (results in deposition in throttle body) • Mechanical System • Ensures continuous supply of fuel 12 Continuous Injection System http://vwts.ru/vw_doc/eva2/FU01/ch5.html 13 Timed Injection System • Fuel injected in port or cylinder at correct time • The Injection timing driven through firing order & piston position during compression stroke • Fuel supply regulated by: ▫ engine speed; inlet manifold vacuum; atmospheric pressure & temp; warm & cold start requirements etc. 14 Gasoline Direct Injection (GDI) • Fuel injected directly into the cylinder • Most accurate method of metered fuel injection • Evaporation of fuel in cylinder volume • Cools the charge • Increase Volumetric efficiency 15 Mitsubishi 1.8L 4G93 GDI • Power 10% ; Fuel Consumption 20% 16 Homogeneous Charge DI • Fuel is injected on same time the air is being drawn into cylinder • Prepares a homogenous charge 17 Stratified Charge DI • Fuel injection just before ignition • Higher compression ratio without “knock” • Small charge of rich fuel burn first • Large charge of lean mixture burns later • High pressure fuel injection 18 Dual Injection System • 2 fuel injectors /cylinder • Engine Performance • Fuel Consumption • Very low exhaust emission • Direct Injection Fraction XDI = 0.3 • Improved Combustion Process 19 Flame Front Propagation v/s xDI Electronic Fuel Injection System Electronic Fuel Injection uses various engine sensors and control module to regulate the opening and closing of injector valve. • Fuel delivery system • Air induction system • Sensor system • Computer control system 21 Fuel Delivery system •Electrical Fuel Pump draws fuel from tank and forces it into the regulator. •Pressure Regulator controls the amount of pressure that enters the injector and any extra fuel is returned to the fuel tank. •Fuel Injector is simply a coil or solenoid operated valve. •Spring pressure holds the injector closed. •When engaged, the injector sprays fuel into the engine. 22 Air Induction System •Air filter •Throttle valve •Sensors •Connecting ducts 23 Sensor System Monitors engine operating condition and reports this information to ECM (computer). • Air Mass Flow Sensor • Oxygen Sensor • Throttle Position Sensor • Engine Temperature Sensor • Engine Speed Sensor • Inlet Air Temperature Sensor • Crankshaft Position Sensor 24 Mass Air Flow Sensor • Measures the amount of outside air entering the engine. • Contains an air flap or door that operates a variable resistor. • Helps computer to determine how much fuel is needed. 25 Oxygen Sensor • It measures the oxygen content in engine exhaust. • Mounted on the exhaust system before the catalytic converter. • Voltage output of O2 sensor changes with the change in oxygen content of exhaust. • Lean mixture decreases the voltage. • Rich mixture increases the voltage. • Signal is sent to ECM and the ECM changes the time that an injector is open or close. 26 Throttle Position Sensor • Variable resister connected to the throttle plate. • Change in throttle angle = change in resistance. • Based on the resistance, ECM richens or leans the mixture. 27 Engine Temperature Sensor • Monitors the operating temperature of the engine. • Exposed to engine coolant. • Engine cold = Low Resistance = Rich Mixture • Engine Hot = High Resistance = Lean Mixture. 28 Inlet Air Temperature Sensor • Measures the temperature of air entering the engine. • Cold air (more dense) = More fuel for proper AF ratio. 29 Crankshaft Position Sensor • Detects engine speed • Changes injector timing and duration • Higher engine speed = More fuel 30 Computer Control System • Uses electrical data from the sensors to control the operation of the fuel injectors. • Engine Control Module (ECM)- “Brain” of the electronic fuel injection.