“Engine tweaking for better performance (continued)”

Motoring corner  With Carlover YOU still need more power than the manufacture put in the hood of your car?

Motoring corner    With Carlover

YOU still need more power than the manufacture put in the hood of your car?

This may sound weird; you can actually make most engines perform better in some circumstances by injecting water directly into the fuel-air mixture. It sounds counterintuitive but the principal is really simple. Vaporising water into the fuel-air mix will cause the air to become denser and cooler. Cool, dense air results in a better charge into the cylinder head, which results in a more powerful burn during combustion. This naturally results in more power. Water injection is used on WRC (World Rally Championship) cars but is detrimental to power when the charge air temperature is below 42°C and boost pressure is below 0.6BAR. Because of this a triggering / shut off system is used on some WRC cars that triggers on at 42°C and shuts back off at 38°C, only triggering when boost is above 0.6BAR.

Inter-cooling, this takes a slightly different poke at the “cooling the fuel-air mix” equation. Intercoolers are normally found on turbo engines and are designed so that atmospheric air flowing around the outside of them cools the air charges from the turbo inside them. The cooler air for the outside can be direct- or indirect-flow. Direct flow designs have the intercooler mounted at the front of the car in the airflow. Indirect-flow units are mounted somewhere in the engine bay with hoses and scoops to get the air to them.

Water-assisted inter-cooling, is an enhancement to standard inter-cooling is water-assisted inter-cooling as found on the Subaru WRX STi. Rather than using water injection into the fuel-air charge, it has an intercooler water spray system that sprays water onto the outside of the intercooler to improve the efficiency of the charge air cooling. The auto version found on the top spec models is ECU-controlled to give 5 second bursts of cooling water when boost is high enough to warrant it. The lower spec versions have a manual switch on the dash that triggers a 5 second burst every time you press the button.

Charge cooling, are a more sophisticated derivative of water-assisted inter-cooling. Rather than just spraying water around the outside of the intercooler, they have a water jacket around the core with an external water pump and independent radiator.

The pump constantly circulates water through the charge-cooler jacket and then out to the radiator, keeping the whole unit cool. Charge-coolers work well until the engine starts being more demanding about power - once they get to a certain point; they’re overwhelmed by the amount of air being drawn into the engine.

Refrigerated inter-cooling / charge-cooling, rather than injecting water directly into the air flow, or cooling the body of the charge-cooler or intercooler, refrigerated systems force the incoming air over a radiator-like device to cool the air. This heat exchanger is filled with a compressed-gas based and works just like your refrigerator at home. The gas is compressed into a liquid then piped into the heat exchanger. As it turns back into gas, it cools down and hence cools the air flowing over the heat exchanger. The now-gaseous coolant is re-compressed outside the intercooler where it gives off the heat via a secondary radiator positioned in the airflow.



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