Combustion chamber design
Advances in software are allowing design engineers to quickly optimise an engine’s ability to generate power
WHAT HAPPENS inside the cylinders of an internal combustion engine isn’t an easy process to comprehend. Exploding pressurised air and fuel makes for a hostile environment, and it’s contained in inches of cast metal. Yet understanding how these reactants move as valves open and pistons retract is incredibly useful if you want to design an engine.
Determining the perfect angle for the valves and the optimum position for a spark plug isn’t guesswork anymore, but that’s only because years of testing and endless prototypes have helped inform engine designers. Today, however, Computational Fluid Dynamics, or CFD, is used to provide an insight into the flow patterns of liquids and gases that are difficult or expensive to study using traditional techniques, and it can be used to give engine designers a much more accurate idea of how fuel burns and gases flow through an engine without having to make prototype parts or spend hours pounding a test track.
One company that uses CFD is Ilmor Engineering. Based in Northampton and founded in 1984, Ilmor has been contracted to create engines for road car manufacturers but has also designed race engines for IndyCar, GT3, WRC and F1.
Ilmor uses a CFD program called Converge (which created the graphics above) to simulate its designs. The software was created by engine specialists and is able to represent knocking/pre-ignition and flame propagation.
Now, you’re probably thinking that once Ilmor has created the ideal combustion chamber and port angles for, say, a four-valve-percylinder head, with or without the help of CFD, it can just implement that design across all its engines. Well, it isn’t that simple. The knowledge gained from one engine will, of course, inform another, but whether the engine is naturally aspirated or turbocharged makes a huge difference on the ideal valve and intake port angles. And, of course, an engine’s layout will dictate what can be achieved. So the CFD software is used to find the optimal position and shape for each element in whatever variation.
The software is also used to optimise existing engines. Ilmor is using Converge to improve the design of the inlet ports, chambers and piston crowns of the 2.2-litre twin-turbo Chevrolet V6 it builds for IndyCar. Ilmor says this saves eight weeks of development time compared with using the traditional method of making parts and then testing them on a dynamometer.
However, even with the ability to accurately simulate combustionchamber dynamics, Ilmor hasn’t seen huge power improvements from using CFD, rather a series of small gains in performance and efficiency. And despite the ability to be far more experimental and try more radical ideas, Ilmor hasn’t learnt anything that has revolutionised the way it builds engines. But that doesn’t mean the software isn’t useful or powerful enough – Ilmor’s engineers find the data invaluable for confirming what they already know from the company’s 30 years of experience, and it’s saved them countless hours and tons of aluminium.
There’s no need to make
prototype engine parts or spend hours pounding a test track