Just a quick one on what I’ve been up to the last few days. I now have the engine set up inside so that I don’t have to keep pushing it outside or waiting for the rain to stop. I’ve also set up an optical encoder, in-cylinder pressure sensor, and AVL IndiSet high speed data acquisition unit to capture data on a 0.25 degree crank angle resolution.
The exhaust manifold was adapted to fit a flexi hose on which then runs through a hole in the wall. This worked pretty well after messing around having problems with old fuel, jamming fuel injector and flat batteries, I got a little running time yesterday. There was a problem with the exhaust being too hot and overheating the rubber exhaust hose (which is designed for water cooled marine exhausts). We extended the length of the metal exhaust manifold which has helped a little, but this may need some water cooling still to solve the problem.
The most interesting part for me was setting up the high speed data acquisition unit and actually capturing some in-cylinder pressure data and accurate ignition and fuel injection timing data. The ability to see this data is pretty fantastic, and is not something that you could ever normally expect to see on an engine under normal operation.
The in-cylinder pressure sensors are very expensive, and this one in particular since it is built into a custom spark plug! I’ll go into details on how this system has to work later, but basically, it provides the most detailed information you could hope to get about combustion inside the engine (without using lasers and optical engines!). The data is very high resolution in both time and value, and allows for events to be compared on a cycle by cycle basis.
By comparison, a good lambda oxygen sensor might react in 80ms, by which time at 6000 RPM the crank shaft will have gone through 8 full revolutions. The high speed data unit can sample information 1440 times per revolution. This requires some pretty special electronics involving high speed ADCs. At any rate, this is great for my project, and I will post some pictures later. More pics here: http://www.flickr.com/photos/gadgit/9100619255/in/set-72157633929512218
P.S. At this point, my software is pretty much already capable of doing everything that is needed of a very simple DIY engine management with electronic fuel injection and electronic ignition. This would be suitable for any single cylinder engine such as for a lawn mower, go kart or motorbike. The software supports closed loop control with a lambda sensor, and has an ignition and fuel injection timing map.