In-cylinder pressure measurement

How could in-cylinder pressure measurement save your engine?

The science of combustion could be your key to maximising engine performance and understanding engine failures.

High performance motorsport engines complete over 200 ignitions within a blink of an eye. At the point of combustion, instantaneous gas temperatures can reach 2,600 degC. This extreme in-cylinder environment can cause a variety of engine issues, yet be impossible to determine. This can leave you feeling frustrated, out of pocket and anxious about meeting project deadlines.

Engine issues

Unfortunately, this happened to one of our clients. They experienced multiple failures on their direct injection engine and they could not afford any more. Despite months of trial and error, neither they nor the build shop could identify the problem.

To compound matters, the original engine manufacturer would not warranty a high-spec engine calibration. With no solution and deadlines looming, the client turned to Collins Limited to see if we could help solve their problem.

Scientific approach

Our first step was to create a plan which ensured the client would still deliver their original engine programme on time. The key to achieving this was to conduct a thorough investigation into the root cause of the issue.

After examining data from knock and exhaust gas temperature sensors, there was no sign of a problem. Yet there was physical evidence of piston ring-land failures, blackened piston crowns and failed con rods. It was clear that a more comprehensive combustion analysis was required. Therefore, we devised a test programme which combined physical testing on a rolling road dynamometer with dynamic mechanical simulations.

To identify the issue, we needed to know what was occurring within the cylinder and therefore measure the in-cylinder pressure. However, commercially available kits exceeded the budget of our client, so we took the initiative to develop and build our own.

In-cylinder pressure measurement kit

‘Our approach to solving technical problems is to start with the physics,’ says Jenner Collins, co-founder of Collins Limited.

‘The pressure in the cylinder is converted to motion at the crankshaft, which is the single reason a vehicle moves. Parameters such as exhaust gas temperature and knock are secondary measurements. We wanted to understand what was happening in terms of the primary data source because everything else is downstream from that. That’s why we developed our own hardware to measure the internal pressure of the cylinder.’

The hardware uses a Optrand fibre optic pressure sensor, along with a data logger, power supply, PC, crank angle sensor and our own bespoke combustion analysis software. Armed with this new capability, we found pressure spikes more than one and a half times the recommended limits during dyno testing. Yet, these were completely undetected by onboard knock sensors.
The next step was to feed the measured pressures into our mechanical simulation. Here, we discovered the pressure spikes subjected the con rod to mechanical stresses more than twice the manufacturers recommendations. No wonder the engine had failed. Pre-ignition was the source of the issue and since, has been found to be common in high performance, direct injection combustion engines.

The solution

Equipped with this new information validated by simulation, we were able to provide this to the engine calibration engineers. They now had what they needed to understand the problem and modify the calibration, preventing further engine failures. Our client not only had their problem solved but met their original deadlines and performance targets.

‘One of the most amazing things we discovered was the fact that successive cylinder firings can result in peak pressures that are up to 10% different. This will be a function of the aerodynamic regime entering the cylinder and the mechanics of combustion, among many elements,’ explains Jenner.

‘It’s a very chaotic environment and this hardware has begun to shine a light on what is happening in the cylinder. It was fantastic to find the root cause of this engine issue and we now have the capability of find your next performance step too.’

If you’d like to understand how this tool could support you next development program, click here to find out.

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