But what is the rising rate regulator and what does it do? To answer that question, let's look at a typical electronic fuel injection system for a gasoline engine. A typical EFI system utilizes an electric fuel pump which runs constantly. The fuel is sent to the fuel rail. On the other end of the fuel rail is a fuel pressure regulator, which bypasses a certain amount of fuel back to the fuel tank in order to maintain a constant fuel pressure in the rail, as set on the regulator. This allows the fuel injectors to vary fuel mixture just by modulating the pulse width of the injector.
There's one problem with this concept though; in a gasoline engine, the pressure in the intake manifold or inlet ports, where the injectors are located is constantly changing, based on rpm, throttle position, and in the case of the turbocharged engine, boost pressure. Manifold pressure can go from, say, 25 inches of vacuum (negative pressure) all the way up to, say 15 psi of positive (boost) pressure. Even though the pressure in the fuel rail is constant, the injector is "seeing" varying pressures in the manifold, therefore the effective pressure at the injector can fluctuate, which would make the fuel injection system unstable and unpredictable. For example, let's say the pressure in the fuel rail is 30 psi of fuel pressure, and the pressure in the manifold is at 0 psi. Pressure at the injector would be 30 psi. However, let's say that the turbo is producing 5 psi of boost pressure. Now, the injector pressure would only be 25 psi, and, in effect, the engine would be getting less fuel at a time when it needed more fuel.
To overcome this problem, most fuel pressure regulators are "manifold referenced." This means that there is a signal line from the manifold to the regulator that tells the regulator what the manifold pressure is, and actually causes the regulator to adjust fuel pressure to compensate for changes in manifold vacuum or pressure. A manifold referenced regulator always provides a 1:1 change in fuel pressure as related to manifold pressure, and are extremely common on fuel injected engines.
The rising rate of gain fuel pressure regulator takes this concept a step further, and it would generally be used in a situation where an electronic fuel injected engine is retrofitted with a forced induction system, either a turbocharger or a supercharger. A rising rate regulator, in theory, would allow one to add a turbo system to an existing fuel injected engine without altering the fuel injection maps at all. Here's how:
We know that a gasoline engine runs a fuel mixture of between 15.5:1 (lean mixture) to around 11:1. (rich mixture) The electronic fuel injection system is programmed to operate the engine within this range, and the mixture is programmed to vary based on engine rpm and load. However, when forced induction is added, the mixtures across the rpm and load map must change. An engine with forced induction must run richer mixtures across the board, when operating under boost. The reason is that compressing the air produces heat, and heat leads to detonation. Richer mixtures keep the combustion temperatures down which prevent detonation. One way to change the mixtures for a forced induction engine would be to change the fuel maps. However, this requires special software, an engine dyno, and a high level of skill and experience in tuning engines. The rising rate pressure regulator was developed as an alternative to complicated and expensive re-mapping of the EFI control. Instead of changing the injector pulse widths, the rising rate regulator increase the fuel pressure as turbo boost increases. It must increase fuel pressure at an exponential rate to boost pressure, not at a 1:1 rate as a normal, manifold referenced regulator would do.
There's one problem with this concept though; in a gasoline engine, the pressure in the intake manifold or inlet ports, where the injectors are located is constantly changing, based on rpm, throttle position, and in the case of the turbocharged engine, boost pressure. Manifold pressure can go from, say, 25 inches of vacuum (negative pressure) all the way up to, say 15 psi of positive (boost) pressure. Even though the pressure in the fuel rail is constant, the injector is "seeing" varying pressures in the manifold, therefore the effective pressure at the injector can fluctuate, which would make the fuel injection system unstable and unpredictable. For example, let's say the pressure in the fuel rail is 30 psi of fuel pressure, and the pressure in the manifold is at 0 psi. Pressure at the injector would be 30 psi. However, let's say that the turbo is producing 5 psi of boost pressure. Now, the injector pressure would only be 25 psi, and, in effect, the engine would be getting less fuel at a time when it needed more fuel.
To overcome this problem, most fuel pressure regulators are "manifold referenced." This means that there is a signal line from the manifold to the regulator that tells the regulator what the manifold pressure is, and actually causes the regulator to adjust fuel pressure to compensate for changes in manifold vacuum or pressure. A manifold referenced regulator always provides a 1:1 change in fuel pressure as related to manifold pressure, and are extremely common on fuel injected engines.
The rising rate of gain fuel pressure regulator takes this concept a step further, and it would generally be used in a situation where an electronic fuel injected engine is retrofitted with a forced induction system, either a turbocharger or a supercharger. A rising rate regulator, in theory, would allow one to add a turbo system to an existing fuel injected engine without altering the fuel injection maps at all. Here's how:
We know that a gasoline engine runs a fuel mixture of between 15.5:1 (lean mixture) to around 11:1. (rich mixture) The electronic fuel injection system is programmed to operate the engine within this range, and the mixture is programmed to vary based on engine rpm and load. However, when forced induction is added, the mixtures across the rpm and load map must change. An engine with forced induction must run richer mixtures across the board, when operating under boost. The reason is that compressing the air produces heat, and heat leads to detonation. Richer mixtures keep the combustion temperatures down which prevent detonation. One way to change the mixtures for a forced induction engine would be to change the fuel maps. However, this requires special software, an engine dyno, and a high level of skill and experience in tuning engines. The rising rate pressure regulator was developed as an alternative to complicated and expensive re-mapping of the EFI control. Instead of changing the injector pulse widths, the rising rate regulator increase the fuel pressure as turbo boost increases. It must increase fuel pressure at an exponential rate to boost pressure, not at a 1:1 rate as a normal, manifold referenced regulator would do.
Copy/pasted from here: http://www.turbokart.com/BEGi.htm
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