Throttle Controlled PWM for HHO

Jun 01, 2010


There are some people who are implementing a PWM that will adjust duty cycle based on throttle position or engine RPM because they believe it will allow hydroxy to be administered based on fuel consumption; thus having the system make better use of the hydroxy.

At first thought it seems like a noble idea. After all, less gas at low RPM means there will be a smaller mechanical load on the alternator and a smaller amount of gas fed to the engine. At higher RPM’s, there will be more hydroxy going to the engine. This seems like how a fuel injection system works, but in reality it is not even close.

Before I will discuss why it won’t work like a fuel injection system and would negatively effect it instead, I will first describe how a fuel injection system works. This will help many understand why a throttle or RPM controlled system will not work, but it will help you understand how you actually can create a system much like fuel injection or any other fuel system for that matter.

A fuel injection system requires a fuel tank, a fuel pump, a fuel pressure regulator, a fuel manifold (or fuel pipe as it is referred to),  fuel lines, fuel injectors and of course a computer that will conduct the orchestra. The fuel pump has one function and that is to provide fuel pressure. The pressure regulator is designed to keep the pressure in the fuel manifold at a consistent pressure behind the fuel injectors. With a consistent pressure, it assures the system that no matter how fast or slow the engine is turning, the same amount of fuel will enter the combustion chamber with a given pulse to the injector. The longer the pulse to the injector, the more fuel enters the cylinders making the engine accelerate. The same principal is used with a can of spray paint. The button on a can of spray paint delivers the same amount of paint each time because the pressure in the can remains virtually consistent. Of course when the spray can is almost empty, less paint comes out; this is because the pressure is much lower than when the can was full.

Now let’s compare this to a system that uses a throttle position sensor or RPM sensor to control duty cycle. The big difference between the two is latency in gas production. The PWM has very little control over gas delivery. It takes several seconds just for enough pressure to build up in the reservoir before the flow is able to increase; you can easily verify this yourself with your current system. When you are idling, it will deliver a small amount of gas which is good, but the pressure will be low which is not good. When you accelerate, the gas pressure which is already low will instantly drop to zero briefly as the vacuum on the reservoir increases. Because of this sudden pressure drop, hydroxy gas delivery at the time of acceleration will be significantly lower (much like the spray can example mentioned before) if not non-existent; and this is the time when you need as much gas as you can get! Since acceleration only takes a couple of seconds before the transmission switches into high gear and the RPM stabilizes at a lower speed, the PWM misses the mark by a long shot! Using this method would be not much different than leaving the injectors wide open, disabling the fuel pressure regulator and relying on a PWM to control the fuel pump based on throttle position. Your car would be shuddering all over the place if it would even start at all; so you could imagine how it would react if you used this method for hydroxy delivery! Pressurized fuel injectors are fast because they need to be; when they open, the gas delivery is instantaneous with no delay or time require to build up pressure which guarantess quick acceleration.

So what can be done to make the system much like the fuel injection model? The PWM is kind of like the fuel pump in a fuel injection system. All it does is create pressure in the gas reservoir. The hose that connects to the intake is really what governs the flow because it has a fixed inside diameter and a fixed length; as long as it is connected to the intake before the throttle, the flow will increase in direct proportion to the increased vacuum during acceleration. If the gas pressure in the reservoir was fixed at a certain pressure, this method would work quite well. You would need to operate the PWM with a gas pressure switch which would turn the PWM on when the pressure dropped below the target pressure and will turn off when it reached the target pressure. The KZX1250 is already set up to handle this. All you need to do is install a gas pressure switch in your reservoir that will switch a ground signal on to the disable terminal whenever the pressure reached the target pressure and release it every time it fell below it. The KZX1250 will turn on and off to keep the pressure at the target setting no matter how fast or slow the engine is running. When you are idling, the flow will be low (due to vacuum) and the PWM will be mostly off; but the pressure will be there. When you accelerate, the PWM will turn on as the pressure just starts to drop. If the reservoir is big enough, there will be enough gas available for the acceleration until the generator is able to restore full pressure. This will give you the quick response you are looking for; much like a fuel injection system.

Trying different things can be frustrating, but trying something that doesn’t work on paper is even more frustrating. So if you want to implement such a system, do it in a way that makes sense on paper first. It will save you money and a great deal of head banging.

- Regards, FreeMindResearch

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