Water injection in SAAB engines

Key words: injector, anti Nox, depollution, low Nox, Trionic, water, performance, power, Saab, Ecopower, octane, detonation, Turbo

Water injection by SAAB

Written by David Scott in Automotive Engineer, translated and adapted by Christophe Martz.

 

Automotive Engineer


Automotive Engineer, Vol. 21, No 1, February-March 1996

According to Saab, water injection is favorable for pollution control.

Water injection is nothing new, during WWII it was used to increase the power of piston engine airplanes.

Now Saab has updated this old technology, not to increase the power but to control the pollutant emissions, especially during the demands of heavy loads (high speeds or strong accelerations).
The 2.3L Ecopower 4 engine has been requested to operate at stoichiometry (lambda = 1) in all driving conditions.

Dr Per Gilbrand is carrying out very promising experiments in this area. He is director of the department "
“Drive Line Concepts” in Sodertalje, Sweden. This department was responsible for the work on Turbocharged engines for the manufacturer Saab.

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Mr Gilbrand claims that water injection can reduce fuel consumption by 15 to 25%, with a significant reduction in HC and Nox emissions. Installation on a vehicle is simplified by simply using the washer reservoir, which limits the installation of the system to a simple pump injector which supplies the 4 cylinders.

Water injection system
Water injector system

"The water in the windshield washer fluid is already antifreeze thanks to the alcohol, which gives a (small) additional benefit as a secondary fuel" explains Mr Gilbrand. "In addition to cooling the combustion chambers at high speeds, the water injection also protects the catalytic converter from overheating."

The system is only operational during the phase of maximum acceleration and when the car exceeds 220 km / h. The injection of water into the intake manifold is electronically managed by Saab's 32-bit Trionic regulation system. The system is therefore directly linked to the demand for power.

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Powers with and without water injection


Graph of power in limited pollutant emissions with and without water injection

The Lambda probe measures the oxygen content of the exhaust and makes it possible to calculate the optimum quantities of air and fuel admitted into the engine. Its function is to maintain the mixture at the best ratio.

The water injection only intervenes when the engine speed is above 3000 rpm. The accompanying graphics show how much horsepower it achieves while keeping emissions low. Thus without water injection, the power would drop rapidly beyond a certain point to keep the pollution rate below certain values. The consumption of "washer fluid" is shown on the 2nd graph.

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Water consumption seems quite high given the flow rates injected but Gillbrand replies that as the injection is only done intermittently (and at high speed), the capacity of this reservoir is not a real problem.

Injected water flow
Water flow rates injected by the system

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