Fuel Economy, Hypermiling, EcoModding News and Forum - EcoModder.com - View Single Post - A couple of questions about water injection.

Andyman · 02-05-2010, 06:49 PM

I don't agree that the EGR tube is a good place for a water injector. I don't think there is enough air flow there. The EGR usually doesn't work at all near full throttle.

Water injection could dilute the oil with some water. To prevent that, you could turn it off when the engine or the intake air is cold. It might help to heat the water before it gets to the water injector. Also, the system should put a reasonable limit on the water flow. I think I've read that the water flow rate should be about 5% of the fuel flow rate when the water injection is working. That way you would use a maximum of one gallon of water when you use 20 gallons of gasoline.

I don't think you have to get a wideband oxygen sensor to run a lean mixture. If you use one, it might help you to figure out what your fuel mixture is while you drive. You would have a voltmeter monitoring its voltage mounted so you could see it while you drive.

If you lower the voltage of the MAP (manifold absolute pressure) sensor signal with some electronics between the MAP sensor and the ECU (computer) you will lean out the mixture. It would be a good idea to switch off any lean mixture during high load conditions so you don't overheat the pistons or lose engine power. The check engine light will probably go on if you lean out the mixture unless you also send a different voltage signal from the coolant temperature sensor to indicate to the computer that the engine is cold even when it is really warm. Some fuel injection systems use an air flow sensor instead of a MAP sensor so the modifications would be different.

I don't know any reason why you would need an EGT (exhaust gas temperature) gauge. I suppose the amount of water injection will affect the exhaust temperature. I don't know much about that. I just know that a low exhaust temperature is an indicator of high efficiency.

I don't think you should have manual control of the water flow rate. It would be too much of a distraction while driving. The control system should control the flow rate according to the speed and load of the engine. I guess it could be as simple as a relay connected to a tachometer circuit and a vacuum switch. The water injection could turn on whenever the engine speed and load exceed a certain level. It would be much better to have a variable water flow rate.

02-05-2010, 06:49 PM	#2 (permalink)
Andyman amateur mech. engineer Join Date: May 2008 Location: New York City Posts: 112 Sporty Accord - '88 Honda Accord LX-i 90 day: 23.25 mpg (US) Dad's Camry - '01 Toyota Camry CE 90 day: 22.81 mpg (US) Artie's Camry - '98 Toyota Camry 90 day: 37.3 mpg (US) Thanks: 0 Thanked 17 Times in 4 Posts	I don't agree that the EGR tube is a good place for a water injector. I don't think there is enough air flow there. The EGR usually doesn't work at all near full throttle. Water injection could dilute the oil with some water. To prevent that, you could turn it off when the engine or the intake air is cold. It might help to heat the water before it gets to the water injector. Also, the system should put a reasonable limit on the water flow. I think I've read that the water flow rate should be about 5% of the fuel flow rate when the water injection is working. That way you would use a maximum of one gallon of water when you use 20 gallons of gasoline. I don't think you have to get a wideband oxygen sensor to run a lean mixture. If you use one, it might help you to figure out what your fuel mixture is while you drive. You would have a voltmeter monitoring its voltage mounted so you could see it while you drive. If you lower the voltage of the MAP (manifold absolute pressure) sensor signal with some electronics between the MAP sensor and the ECU (computer) you will lean out the mixture. It would be a good idea to switch off any lean mixture during high load conditions so you don't overheat the pistons or lose engine power. The check engine light will probably go on if you lean out the mixture unless you also send a different voltage signal from the coolant temperature sensor to indicate to the computer that the engine is cold even when it is really warm. Some fuel injection systems use an air flow sensor instead of a MAP sensor so the modifications would be different. I don't know any reason why you would need an EGT (exhaust gas temperature) gauge. I suppose the amount of water injection will affect the exhaust temperature. I don't know much about that. I just know that a low exhaust temperature is an indicator of high efficiency. I don't think you should have manual control of the water flow rate. It would be too much of a distraction while driving. The control system should control the flow rate according to the speed and load of the engine. I guess it could be as simple as a relay connected to a tachometer circuit and a vacuum switch. The water injection could turn on whenever the engine speed and load exceed a certain level. It would be much better to have a variable water flow rate.