Maximus
12-18-05, 01:24 AM
Gasoline or Diesel
The calibration, and often the design, of a fuel injection system differ depending on the type of fuel: propane (LPG), gasoline, alcohol, methane (natural gas), hydrogen or diesel. The vast majority of fuel injection systems are for gasoline or diesel applications and to a lesser extent for LPG, and in the past, the designs were quite different. With the advent of EFI, the two systems have grown similar in concept, but the nature of the fuels and their respective combustion characteristics will continue to require differences in their systems.
* Diesel
o At one time, nearly all diesel engines used high-pressure "mechanical injection", i.e., not "electronic injection".
o Diesels are rapidly adopting EFI, which is based on an electronic fuel injector similar to a modern gasoline application.
* Gasoline
o Prior to EFI, it was extremely rare for an automobile engine to be equipped with fuel injection. If it was, it was most likely a low-pressure mechanical system of "immature" technology. These early systems were generally used on exotic performance vehicles, or for racing.
o Robert Bosch GmbH, and Bendix introduced the first electronic injection systems starting in the 1950s, and they were quite dissimilar to today's EFI. (#Evolution)
Detailed Function
Note: The following description applies to a modern EFI gasoline engine. Parallels to a diesel can be made, but only conceptually.
Typical EFI Components
* Injectors
* Fuel Pump
* Fuel Pressure Regulator
* ECU - Electronic Control Unit; includes a digital CPU, and circuitry to communicate with sensors and control outputs.
* Wiring Harness
* Various Sensors (Some, of the sensors required are listed here.)
* Crank/Cam Position: Hall effect sensor
* Airflow: MAF sensor, sometimes this is inferred with a MAP sensor
* Exhaust Gas Oxygen: O2 Sensor, Oxygen sensor, EGO sensor, UEGO sensor
A contemporary EFI system requires a number of sensors to measure the engine's operating conditions. A CPU interprets these conditions in order to calculate the amount of fuel, among numerous other tasks. The desired “fuel flow rate†depends on several conditions, with the engine’s “air flow rate†being the fundamental factor.
The electronic fuel injector is normally closed and opens to flow fuel as long as an electric pulse is applied to the injector. The pulse’s duration (pulsewidth) is proportional to the amount of fuel desired. The pulse is applied once per engine cycle, which permits pressurized fuel to flow from the fuel supply line, through the open injector, into the engine’s air intake, usually just ahead of the intake valve.
Since the nature of fuel injection dispenses fuel in discrete amounts, and since the nature of the 4-stroke-cycle engine has discrete induction (air-intake) events, the CPU calculates fuel in discrete amounts. The fuel quantity is tailored for each individual induction event. In other words, every induction event, of every cylinder, of the entire engine, is a separate calculation, and each injector receives a unique pulsewidth based on that cylinder’s fuel requirements.
It is necessary to know the amount (actual mass) of air the engine "breathes" during each induction event. This is proportional to the intake manifold’s air pressure, which is proportional to throttle position. The amount of air inducted, known as "air-charge", can be determined using one of several methods, but they are beyond the scope of this topic. (See MAF sensor, or MAP sensor.)
Note: The right pedal is not the gas pedal; it is the air pedal. The throttle pedal determines the air, and in turn, the airflow determines the fuel. The same is true for carburetors. With some recent systems, the right pedal isn't even an "air pedal"... it has evolved to a "power demand pedal" - it isn't connected to the throttle at all, it just signals to the CPU how far the driver has pushed it down, and it is then up to the CPU to open the throttle using a small electric motor. This has some benefits for controlling emissions during transients, and makes it easy and cheap to implement cruise control.
The three elemental ingredients for combustion are fuel, air and ignition. The sensors and CPU interpret the air mass in order to calculate the fuel mass. The nominal (chemically correct) air/fuel ratio is 14.64:1, by weight for gasoline. This "molar balanced" ratio is called stoichiometry.
Deviations from stoichiometry are required during non-standard operating conditions such as heavy load, or cold operation, in which case, the mixture ratio can range from 10:1 to 18:1 (for gasoline).
Note: The stoichiometric ratio changes as a function of the fuel; diesel, gasoline, ethanol, methanol, propane, methane (natural gas), or hydrogen. Additionally, "flexible fuel" vehicles permit refueling with gasoline, and/or an alcohol, resulting in all possible blends in the tank. These EFI systems must be able to identify the blend and compensate accordingly.
Additionally, final pulsewidth is inversely proportional to fuel line pressure and injector size. A larger capacity injector, or higher fuel line pressure, will inject more fuel for the same pulsewidth. Compensation for these and many other factors are programmed into the CPU's software.
In summary, the vehicle operator opens the engine’s throttle (right pedal), the sensors measure airflow, the CPU calculates the desired air/fuel ratio, and then outputs a pulsewidth providing the accurate mass of fuel for efficient combustion. This process is repeated every time an intake valve opens.
The modern EFI system treats each injection as series of discrete events, which when all strung together, perform one, smooth, seamless experience. An oversimplified analogy is that it is not unlike a motion picture that appears to move from a series of individual images
The calibration, and often the design, of a fuel injection system differ depending on the type of fuel: propane (LPG), gasoline, alcohol, methane (natural gas), hydrogen or diesel. The vast majority of fuel injection systems are for gasoline or diesel applications and to a lesser extent for LPG, and in the past, the designs were quite different. With the advent of EFI, the two systems have grown similar in concept, but the nature of the fuels and their respective combustion characteristics will continue to require differences in their systems.
* Diesel
o At one time, nearly all diesel engines used high-pressure "mechanical injection", i.e., not "electronic injection".
o Diesels are rapidly adopting EFI, which is based on an electronic fuel injector similar to a modern gasoline application.
* Gasoline
o Prior to EFI, it was extremely rare for an automobile engine to be equipped with fuel injection. If it was, it was most likely a low-pressure mechanical system of "immature" technology. These early systems were generally used on exotic performance vehicles, or for racing.
o Robert Bosch GmbH, and Bendix introduced the first electronic injection systems starting in the 1950s, and they were quite dissimilar to today's EFI. (#Evolution)
Detailed Function
Note: The following description applies to a modern EFI gasoline engine. Parallels to a diesel can be made, but only conceptually.
Typical EFI Components
* Injectors
* Fuel Pump
* Fuel Pressure Regulator
* ECU - Electronic Control Unit; includes a digital CPU, and circuitry to communicate with sensors and control outputs.
* Wiring Harness
* Various Sensors (Some, of the sensors required are listed here.)
* Crank/Cam Position: Hall effect sensor
* Airflow: MAF sensor, sometimes this is inferred with a MAP sensor
* Exhaust Gas Oxygen: O2 Sensor, Oxygen sensor, EGO sensor, UEGO sensor
A contemporary EFI system requires a number of sensors to measure the engine's operating conditions. A CPU interprets these conditions in order to calculate the amount of fuel, among numerous other tasks. The desired “fuel flow rate†depends on several conditions, with the engine’s “air flow rate†being the fundamental factor.
The electronic fuel injector is normally closed and opens to flow fuel as long as an electric pulse is applied to the injector. The pulse’s duration (pulsewidth) is proportional to the amount of fuel desired. The pulse is applied once per engine cycle, which permits pressurized fuel to flow from the fuel supply line, through the open injector, into the engine’s air intake, usually just ahead of the intake valve.
Since the nature of fuel injection dispenses fuel in discrete amounts, and since the nature of the 4-stroke-cycle engine has discrete induction (air-intake) events, the CPU calculates fuel in discrete amounts. The fuel quantity is tailored for each individual induction event. In other words, every induction event, of every cylinder, of the entire engine, is a separate calculation, and each injector receives a unique pulsewidth based on that cylinder’s fuel requirements.
It is necessary to know the amount (actual mass) of air the engine "breathes" during each induction event. This is proportional to the intake manifold’s air pressure, which is proportional to throttle position. The amount of air inducted, known as "air-charge", can be determined using one of several methods, but they are beyond the scope of this topic. (See MAF sensor, or MAP sensor.)
Note: The right pedal is not the gas pedal; it is the air pedal. The throttle pedal determines the air, and in turn, the airflow determines the fuel. The same is true for carburetors. With some recent systems, the right pedal isn't even an "air pedal"... it has evolved to a "power demand pedal" - it isn't connected to the throttle at all, it just signals to the CPU how far the driver has pushed it down, and it is then up to the CPU to open the throttle using a small electric motor. This has some benefits for controlling emissions during transients, and makes it easy and cheap to implement cruise control.
The three elemental ingredients for combustion are fuel, air and ignition. The sensors and CPU interpret the air mass in order to calculate the fuel mass. The nominal (chemically correct) air/fuel ratio is 14.64:1, by weight for gasoline. This "molar balanced" ratio is called stoichiometry.
Deviations from stoichiometry are required during non-standard operating conditions such as heavy load, or cold operation, in which case, the mixture ratio can range from 10:1 to 18:1 (for gasoline).
Note: The stoichiometric ratio changes as a function of the fuel; diesel, gasoline, ethanol, methanol, propane, methane (natural gas), or hydrogen. Additionally, "flexible fuel" vehicles permit refueling with gasoline, and/or an alcohol, resulting in all possible blends in the tank. These EFI systems must be able to identify the blend and compensate accordingly.
Additionally, final pulsewidth is inversely proportional to fuel line pressure and injector size. A larger capacity injector, or higher fuel line pressure, will inject more fuel for the same pulsewidth. Compensation for these and many other factors are programmed into the CPU's software.
In summary, the vehicle operator opens the engine’s throttle (right pedal), the sensors measure airflow, the CPU calculates the desired air/fuel ratio, and then outputs a pulsewidth providing the accurate mass of fuel for efficient combustion. This process is repeated every time an intake valve opens.
The modern EFI system treats each injection as series of discrete events, which when all strung together, perform one, smooth, seamless experience. An oversimplified analogy is that it is not unlike a motion picture that appears to move from a series of individual images