Engine simulation software
The emergence of simulation software packages for engine design and testing has revolutionised the race engine industry. Whether it be for the initial design of components, evaluating particular aspects of an engine – for example the valvetrain – or assessing overall performance parameters, engineers can access a plethora of virtual tools to help them.
In the past, comprehensive simulation – for example of gas flow within an engine – was the preserve of high-end commercial software packages. However, this situation is now changing thanks to the appearance and subsequent development of software packages aimed at users who may not have the resources of OEMs or works racing teams. These programs fall broadly into two groups: ‘basic’ simulation packages, which can provide a close approximation of engine performance, and more complex ‘open source’ packages.
The basic packages can range from free-to-use trial version of mainstream software to dedicated commercial packages that do not carry the hefty licence fees of more powerful programs. The open source systems tend to be free to use and are potentially very powerful; however, they usually lack the user-friendly interfaces of commercial systems, so it takes longer to gain useful results from such software. The one major advantage though of this type of software is its open source nature, enabling users who understand it to expand the functionality using their own code. There are even open source CFD solvers suitable for simulating complex in-cylinder gas flows in three dimensions – something that is definitely not included in any ‘basic’ simulation software.
Despite their limitations, even basic engine simulators can provide considerable benefits to engine builders, both from a component optimisation and a time/cost-saving perspective. These types of simulation package tend to focus on a particular area of an engine, helping to keep complexity (and thus the aforementioned cost) low. So which aspects of an engine can be modelled with some of the more commonly available systems?
One of the most frequently investigated areas is camshaft and valvetrain design. Most simulation software will allow users to model lobe profiles and assess their effect on valvetrain motion. Also, depending on a particular program’s capability, the results obtained for such simulation can show factors such as contact stress and oil film thickness at the lobe-lifter interface, as well as more in-depth insights into the valvetrain’s behaviour. For example, the impact of differing profiles on valve spring specification can be determined or, if looking at a pushrod-actuated valve, the impact of pushrod/rocker geometry on efficiency can be examined. The results gained from dedicated valve simulation packages can also often be used as inputs for overall engine models.
Similar to valvetrain simulation, there are also a number of dedicated cranktrain analysis packages available commercially. Beyond the basic requirements for assessing crank, rod and piston movement, some packages allow for other useful factors to be assessed. Wrist pin and rod bolt sizes can be determined, for example, with some software even providing preset piston loadings to work from. In more advanced packages, the con rod design can also be scrutinised for fatigue resistance under particular operating conditions.
Provided that the input data is reliable, even the most basic simulation system can prove very useful for engine development. Much as is the case with the use of CFD for car aerodynamic development, being able to gain an estimate of which combinations of components will produce the best gains – without having to physically build the components – greatly reduces the resources needed for engine development.
While the packages that can be classed as ‘affordable’ will not produce absolutely perfect results, they are still accurate enough to be useful development tools. The free-to-use, open source packages also have the potential to be very powerful, provided that the user has the correct expertise. However, both approaches give engineers tools that were previously only available to high-end manufacturers with deep pockets.
Written by Lawrence Butcher