Water injection benifits emmission, SAAB says Water injection is nothing new. During WWII it was used to increase the power of aircraft piston engines. Now Saab has revived the old technology not to boost power, but to maintain full emmission control in a car engine during peak power demands of high-speed operation and acceleration bursts. It has enabled the 2.3-litre Ecopower four-cylinder engine to run at Lambda 1 under all driving conditions. Promising experiments in this field are being conducted by Dr Per Gillbrand, Manager of the Drive Line Concepts section at Sodertalje, Sweden, who was responsible for Saab's pioneering work in turbocharging and related develpoments. He reports that water injection reduced full-load petrol consumption of the concept engine by 15 to 25%, and with a significant drop in HC and Nox emission. Car installation is simplified by using windscreen washer water from the existing fluid reservoir, which limits additional under-bonnet equipment needed, to a single injector pump feeding the four cylinders.

"The water is already frost-protected by alcohol-based anti-freeze, which gives a secondary benifit as a supplementary engine fuel," Gillbrand explains, "Since the water lowers the combustion chamber temperatures at high speeds it also helps protect the catalytic converter from overheating". The system operates only during period of full-throttle acceleration and then again at road speed above 220km/h. Water injection through special nozzles in the intake manifold is regulated bt Saabs's 32-bit Trionic engine management electronics, and can thus be keyed directly to power demand. The Lambda sensor is in a closed loop between the engine exhaust and ambient air as inputs, and fuel-metering via the ECU on the output side. Its function is to maintain the air-fuel mixture at the optimized ratio for minimal emissions, when Lambda = 1. Injection occurs only at engine speed above 3000r/min, and the accompany graphs show how it enables power to be increased beyond this point with controlled emission. But without injection the power curve must fall off repidly to hold the same low emisson value. Typical washer fluid consumption is shown in the second graph. While the instantaneous quantities seem large relative to the car's washer reservoir capacity, Gillbrand says, the period of actual use are short and intermittent, so he sees no major problem in water supply. by David Scott of Automotive Engineer Vol21 No1 February/March 1996

Top: fluid injection system with (below left) 2.3 litre Ecopower concept engine and (below right) washer fluid consumption