DETROIT - Fuel does strange things in an internal combustion engine.
Unburned hydrocarbons hide in the tiny lip that surrounds the exhaust valve, for instance. Fuel tucks itself away in the ultrathin layer of lubricating oil on cylinder walls. Most of each fuel charge burns during the combustion cycle, but the last bit of exhaust from the cylinder carries the dirtiest gases, including fuel that the flame never reached.
All of those factors affect emissions, sometimes fooling an engine computer into adding the wrong combination of fuel and air to solve the problem.
That's where Combustion Ltd.'s ultrafast analysis equipment comes into play. The 20-person company in Cambridge, England, makes measurement equipment that can subdivide and graph data to show the separate emissions outputs during one beat of one cylinder in a test engine.
The company showed its sensors at the SAE World Congress in March, one of the few gatherings in the world where instruments as esoteric as these gain a lot of walk-in attention.
Tim Hands, a company director, said such graphing is a crucial part of understanding the performance variations in modern engines. Tracking carbon monoxide emissions against carbon dioxide, for example, can show whether one cylinder of an engine is running too rich on each firing cycle.
Similarly, getting information from standard emission sensors only lets engineers infer what might be happening in the cylinder during combustion. Sensors can be fooled: Oxygen sensors may report identical proper levels when combustion is going well and when combustion isn't happening at all, and unburned fuel swamps the sensor.
'You get an inference that has nothing to do with the flame. With fast testing of the exhaust gases, though, it's the level that the flame actually saw,' said Hands. Such testing is going to become crucial as new start/stop engines, driven by 42-volt starter-generators, come to the market. Fuel may be saved by the engine cutoff during traffic stops, but the worst emissions occur during startup - and even during engine cutoff, Hands noted.
That's because fuel injectors cause a small amount of fuel to collect in the cylinder intake, and that fuel is drawn into the engine during nonsparking revolutions that happen just after and just before normal running. Even without the puddled fuel, microscopic amounts of unburned hydrocarbons that have hidden in the engine oil or in cylinder recesses around the valve seats or gasket lines will creep into the exhaust when normal combustion isn't under way.
'Maybe there's no way to correct a given situation, but at least we can show the guy actual data to let him know what that situation is. He's not guessing - and making a wrong guess - from just this one curve,' said Hands.
Knowing the correct calibration to minimize bad circumstances is one result of Cambustion's fast measurement systems; another applies to the rarified world of Formula One racing, where Cambustion equipment actually rides in the exhaust of engines running at 17,000 to 18,000 rpm.