Injection of water into SAAB engines

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

Injection of water 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, the injection of water is favorable to the depollution.

The injection of water is nothing new, during the 2 World War it was used to increase the power of the piston engine aircraft.

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 conducting some very promising experiments in this field. He is director of the department »
Drive Line Concepts in Sodertalje, Sweden. This department was responsible for work on Turbocharged engines for the manufacturer Saab.

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

Water injection system
Water injector system

"The wash water is already antifreeze thanks to the alcohol, which gives a (small) additional benefit as a secondary fuel," explains 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 maximum acceleration phase and when the car exceeds 220 km / h. The injection of water into the intake manifold is electronically managed by Saab's Trionic 32 control bit system. Thus the system is directly related to the power demand.

Powers with and without water injection
Graph of the powers in limited polluting emissions with and without water injection

The Lambda sensor measures the oxygen content of the exhaust and calculates the optimum amounts of air and fuel allowed in the engine. Its function is to maintain the mixture at the best ratio.

Water injection occurs only when the engine speed is greater than 3000 rpm. The attached graphs show how much power it allows while keeping emissions low. Thus without water injection, the power would fall quickly beyond a certain point to keep the pollution rate below certain values. The consumption of "washer" is shown on the 2ieme chart.

Water consumption seems quite important given the flow rates injected but Gillbrand replicates that since the injection is only intermittent (and high speed), the capacity of this tank is not a real problem.

Injected water flow
Flow rates of water injected by the system


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