I’ve been following a series of videos on YouTube of a couple of guys who have been busy building a Briggs and Stratton engine with a transparent cylinder head. They’ve now got it running surprisingly well:
I’ve made another video which talks through the way that the closed loop ignition control system works.
It may help to watch the video explaining the whole system first here: http://scottsnowden.co.uk/?p=337
I’ve made a video of the whole system explaining all of the sensors, actuators and interfaces, and some of the more advanced indicating equipment that I’m using.
A more detailed explanation of the closed loop ignition timing control is given here: http://scottsnowden.co.uk/?p=341
I have been busy over the last few weeks with various things, but have now completed most of the practical work on my project and am now at the stage of writing up the report/dissertation. I have successfully managed to achieve closed loop ignition timing control by using the Stellaris Launchpad development board to directly interface with the optical encoder on the engine and the pressure sensor charge amplifier (this replaces the AVL IndiSet 620 in my system).
In order to run the engine inside, I had to set up an external exhaust to get the fumes outside. This had been done with a big exhaust manifold attached to a flexi rubber marine exhaust hose, and then poked through a hole in the wall. This was ok operating the engine at idle and under low loads, but the rubber hose would get extremely hot under high load high speed conditions. It then began to melt internally and was causing the whole building to smell of burning rubber.
So one of the aims of my project is to use in-cylinder pressure as a means of providing a measurement of what is going on with the engine, and hence use this to in some way control my ignition and fuelling.
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.
More progress made today, I connected up the alternator to the engine to begin testing it under load. This was pretty successful, and the ECU all performed as expected, with only a few tweaks to the PID controller parameters to improve the AFR control. I restricted the range of fuelling down to as restricted as possible to prevent the system setting wildly large or small fuelling amounts under certain conditions. I finally managed to get the PID to maintain the AFR slightly rich within a few percent under steady state conditions.
I have now managed to run the engine with electronic fuel injection (EFI) and electronic ignition, both controlled from my ECU. I’ve also managed to run in closed loop lambda control to maintain the correct air to fuel ratio.
Success! I have started and run the engine on my own electronic ignition. The problem was in the end quite simple, it turns out that the missing tooth wheel on the crank was aligned differently to what I expected. I thought that the missing tooth occurred 240 degrees after TDC, but in fact it appears to be aligned almost exactly at TDC. This meant that my spark was happening around Bottom Dead Centre, which is no use at all!