370 HEMI
11-07-2009, 11:50 AM
Many people have called me and have asked specific questions on the different types of fuel delivery systems and their different names. Many questions too about what does Mass Airflow mean, and what is speed density and what does that really mean.
I thought it would be a good time to educate a little bit on some of the principles of Speed Density and how it functions in our Chrysler designed cars.
Obviously we have to know about these systems to understand how to tune them, how they function, and of course what does ACES IV do in the mix.
Since we all know that our cars are computer controlled and that they measure the fuel to the engine, we just don't really understand how it is done.
Once you get past a carburetor, it becomes like a black art or something because we know we have fuel injectors and a pcm and it all functions when we turn the key and we say ok it works and thats about all I know.
For the average person, that is fine, but when you are involved in tuning your car with a Predator or other devices, it becomes important to understand what parameters the systems depend on.
Mass Air Flow is a system that uses exact measurement of air entering the engine as it's primary factor along with crankshaft position to determine the volume of fuel provided to the engine. So basically it monitors air flow and is relatively slow to react. Remember that airflow speeds up and slows down less rapidly than manifold pressure so the PCM control of the fuel supply is not as succinct as is a Speed Density System.
The second type of system is the Density Speed System that uses a MAP (Manifold Absolute Pressure) sensor which is the dominant input to the PCM. The inputs from the Camshaft Position Sensor and the Crankshaft Position Sensors are also required but in a less important capacity. This is a really old system that I do not believe anyone is still using at this time or any longer.
Speed Density Systems are what Chrysler uses and have used for many years on their cars. In a Speed Density System, the PCM uses the MAP sensor and the Crankshaft Position Sensor for determining fuel volume.
This way it monitors engine speed, monitors intake manifold pressure, responds much more rapidly and allows the PCM to closely monitor the engine operating conditions and the base fuel supply on that information. This is a much more accurate system.
Really the engine has to determine load by several factors to calcuate what it needs to know to meter the appropriate fuel.
Manifold Absolute Pressure divided by barometric pressure (baro read sensor)
times current RPM divided by Max potential RPM to determine that load.
So basically air density and speed of the vehicle.
Now, understanding how the PCM determines load, we have to incorporate the other inputs that are necessary for determining the injector pulse width.
This can be determined by this expression:
Load x TPS x ECT x IAT x BAT x LT x O2 x ST = Pulse Width.
TPS = Throttle Position Sensor - which provides information on the current mode of operation (idle, off-idle acceleration, etc.) and performs various operating strategies. When the TPS increases rapidly for example, the injector pulse width is greatly increased to deliver the amount of fuel required.
ECT = Engine Coolant Temperature which is the second biggest modifier of pulse width after the MAP. If the engine is cold, fuel will not atomize as easily (see summer vs winter fuel post) so the PCM will add extra fuel depending on the value from the ECT. This is where the ignition improver of the ACES IV works well to get the fuel molecularly balanced to atomize and ignite quicker in cold weather.
If the engine is hot, of course fuel volume will be altered accordingly. If your ECT signal is ever lost, the PCM will substitute a preset value and the limp in mode would be triggered.
IAT = Intake Air Temperature (also known as Charge Temperature Sensor from years ago). If the ECT shows High and the IAT shows cold (dense air) then the PCM will add extra fuel. If the air is hot (thin) then the spark advance is adjusted accordingly.
If the IAT signal is lost, the PCM will substitute a value based on the battery signal and the Ambient Temperature Sensor.
BAT = Sensed Battery Voltage. Remember that injectors are rated for specific flow at specific voltages. If battery voltage is lower than the injector rating, it will take longer for the injector to open and it may not open as far, so the PCM needs to know the voltage to compensate by changing the pulse width. In some vehicles the IAT and BT are combined and called the Inlet Air Temperature Sensor.
LT = Short Term and Long Term Adaptives - the short term adaptive memories allow the PCM to do two things. First it gives it the capability to change injector pulse width to bring the O2 Sensor to its midrange of operation. Second, it allows for storage of corrections required for specific operating conditions (long term). This is what starts to change due to the changes in fuels at the refinery. Changes occur in the energy content and allow the adaptives to change. ACES IV tends to help bridge the gap between the highs and lows by smoothing energy release.
O2= Oxygen Sensors. The PCM looks at the O2 signal to determine how well it did on the BASE pulse width calculation. The data provided by the O2 Sensor signal tells the PCM how much oxygen was left over after the combustion process. Adaptations are withheld until closed loop conditions exist.
ST= Short Term and Long Term Adaptives - the short term adaptive memories allow the PCM to do two things. First it gives it the capability to change injector pulse width to bring the O2 Sensor to its midrange of operation. Second, it allows for storage of corrections required for specific operating conditions (long term). This is what starts to change due to the changes in fuels at the refinery. Changes occur in the energy content and allow the adaptives to change. ACES IV tends to help bridge the gap between the highs and lows by smoothing energy release.
With all the defined inputs being provided, the PCM provides the determined pulse width (the time the injector is open spraying fuel) control to energize the fuel injectors. As the PCM increases or decreases this pulse width, the amount of fuel released into the combustion process is increased and or decreased.
Many discussions I have had with customers is getting the air/fuel ratio as close to Stoichiometric.
This is the ideal result to keep the amount of fuel injected into the engine as reasonably close to the value of 14.7 parts of air to 1 part of fuel. Also expressed as 14.7 to 1. This ratio results in the best engine performance, the highest fuel economy, and the least emissions (lightest black in the exhaust tips/pipes etc.)
By the way, when the engine is cold, it is in what is called open loop. This is when there is no O2 sensor information used, predetermined base fuel calculations are used and the O2 sensors are not adapted at all.
As the engine warms up, then it goes to closed loop. Now O2 sensor information is utilized by the PCM to alter the base fuel calculations.
The sooner that your car reaches closed loop operation the better the fuel economy and power is achieved without excessive washdown creating acids etc.
Hopefully this will help many understand the basics of what a Speed Density System is and how it functions, how it compares to a Mass Airflow System and a Density Speed System.
When you can understand how this works, it gives you a better grasp of why ACES IV can produce more power with less fuel as the utilization of fuel energy is transferred from potential to kinetic energy.:beerchug:
Regards,
Brian
BND Automotive LLC:driving:
440-821-9040
I thought it would be a good time to educate a little bit on some of the principles of Speed Density and how it functions in our Chrysler designed cars.
Obviously we have to know about these systems to understand how to tune them, how they function, and of course what does ACES IV do in the mix.
Since we all know that our cars are computer controlled and that they measure the fuel to the engine, we just don't really understand how it is done.
Once you get past a carburetor, it becomes like a black art or something because we know we have fuel injectors and a pcm and it all functions when we turn the key and we say ok it works and thats about all I know.
For the average person, that is fine, but when you are involved in tuning your car with a Predator or other devices, it becomes important to understand what parameters the systems depend on.
Mass Air Flow is a system that uses exact measurement of air entering the engine as it's primary factor along with crankshaft position to determine the volume of fuel provided to the engine. So basically it monitors air flow and is relatively slow to react. Remember that airflow speeds up and slows down less rapidly than manifold pressure so the PCM control of the fuel supply is not as succinct as is a Speed Density System.
The second type of system is the Density Speed System that uses a MAP (Manifold Absolute Pressure) sensor which is the dominant input to the PCM. The inputs from the Camshaft Position Sensor and the Crankshaft Position Sensors are also required but in a less important capacity. This is a really old system that I do not believe anyone is still using at this time or any longer.
Speed Density Systems are what Chrysler uses and have used for many years on their cars. In a Speed Density System, the PCM uses the MAP sensor and the Crankshaft Position Sensor for determining fuel volume.
This way it monitors engine speed, monitors intake manifold pressure, responds much more rapidly and allows the PCM to closely monitor the engine operating conditions and the base fuel supply on that information. This is a much more accurate system.
Really the engine has to determine load by several factors to calcuate what it needs to know to meter the appropriate fuel.
Manifold Absolute Pressure divided by barometric pressure (baro read sensor)
times current RPM divided by Max potential RPM to determine that load.
So basically air density and speed of the vehicle.
Now, understanding how the PCM determines load, we have to incorporate the other inputs that are necessary for determining the injector pulse width.
This can be determined by this expression:
Load x TPS x ECT x IAT x BAT x LT x O2 x ST = Pulse Width.
TPS = Throttle Position Sensor - which provides information on the current mode of operation (idle, off-idle acceleration, etc.) and performs various operating strategies. When the TPS increases rapidly for example, the injector pulse width is greatly increased to deliver the amount of fuel required.
ECT = Engine Coolant Temperature which is the second biggest modifier of pulse width after the MAP. If the engine is cold, fuel will not atomize as easily (see summer vs winter fuel post) so the PCM will add extra fuel depending on the value from the ECT. This is where the ignition improver of the ACES IV works well to get the fuel molecularly balanced to atomize and ignite quicker in cold weather.
If the engine is hot, of course fuel volume will be altered accordingly. If your ECT signal is ever lost, the PCM will substitute a preset value and the limp in mode would be triggered.
IAT = Intake Air Temperature (also known as Charge Temperature Sensor from years ago). If the ECT shows High and the IAT shows cold (dense air) then the PCM will add extra fuel. If the air is hot (thin) then the spark advance is adjusted accordingly.
If the IAT signal is lost, the PCM will substitute a value based on the battery signal and the Ambient Temperature Sensor.
BAT = Sensed Battery Voltage. Remember that injectors are rated for specific flow at specific voltages. If battery voltage is lower than the injector rating, it will take longer for the injector to open and it may not open as far, so the PCM needs to know the voltage to compensate by changing the pulse width. In some vehicles the IAT and BT are combined and called the Inlet Air Temperature Sensor.
LT = Short Term and Long Term Adaptives - the short term adaptive memories allow the PCM to do two things. First it gives it the capability to change injector pulse width to bring the O2 Sensor to its midrange of operation. Second, it allows for storage of corrections required for specific operating conditions (long term). This is what starts to change due to the changes in fuels at the refinery. Changes occur in the energy content and allow the adaptives to change. ACES IV tends to help bridge the gap between the highs and lows by smoothing energy release.
O2= Oxygen Sensors. The PCM looks at the O2 signal to determine how well it did on the BASE pulse width calculation. The data provided by the O2 Sensor signal tells the PCM how much oxygen was left over after the combustion process. Adaptations are withheld until closed loop conditions exist.
ST= Short Term and Long Term Adaptives - the short term adaptive memories allow the PCM to do two things. First it gives it the capability to change injector pulse width to bring the O2 Sensor to its midrange of operation. Second, it allows for storage of corrections required for specific operating conditions (long term). This is what starts to change due to the changes in fuels at the refinery. Changes occur in the energy content and allow the adaptives to change. ACES IV tends to help bridge the gap between the highs and lows by smoothing energy release.
With all the defined inputs being provided, the PCM provides the determined pulse width (the time the injector is open spraying fuel) control to energize the fuel injectors. As the PCM increases or decreases this pulse width, the amount of fuel released into the combustion process is increased and or decreased.
Many discussions I have had with customers is getting the air/fuel ratio as close to Stoichiometric.
This is the ideal result to keep the amount of fuel injected into the engine as reasonably close to the value of 14.7 parts of air to 1 part of fuel. Also expressed as 14.7 to 1. This ratio results in the best engine performance, the highest fuel economy, and the least emissions (lightest black in the exhaust tips/pipes etc.)
By the way, when the engine is cold, it is in what is called open loop. This is when there is no O2 sensor information used, predetermined base fuel calculations are used and the O2 sensors are not adapted at all.
As the engine warms up, then it goes to closed loop. Now O2 sensor information is utilized by the PCM to alter the base fuel calculations.
The sooner that your car reaches closed loop operation the better the fuel economy and power is achieved without excessive washdown creating acids etc.
Hopefully this will help many understand the basics of what a Speed Density System is and how it functions, how it compares to a Mass Airflow System and a Density Speed System.
When you can understand how this works, it gives you a better grasp of why ACES IV can produce more power with less fuel as the utilization of fuel energy is transferred from potential to kinetic energy.:beerchug:
Regards,
Brian
BND Automotive LLC:driving:
440-821-9040