2 Stroke Mini-mobile: Trials
Well and truly at this point, design is being held back by a lack of variable timing mechanisms. Ignition timing can be tuned slower which improves low-speed torque considerably, however this just results in the vehicle getting bogged down pretty early because it is unable to spin up fast enough to generate sufficient power to overcome the load. Setting it faster permits the motor to spin up to a higher speed and develop more power, but it doesn't generate enough torque to maintain this power for long and bogs down a little farther down the track. Variable ignition timing would allow it to grind as well as spin. Alternatively the engine could be optimized around a more narrow RPM range and a CVT used though I haven't come up with a suitable design yet.
In the end this design required some changes over the last Hillclimb video in order to complete this track - first a reduction gear was added. Originally I was using a 3:1 reduction gear but even with this reduction the load on the engine was too great. The reduction gear seen here is approximately 4:1 which permits the engine to retain more RPM, the net result on the top speed is minimal because now the engine can use more of it's RPM range. The flywheel was replaced with a special low density, high performance version, and fine-tuning done to the combustion chamber and seals to permit the maximum force with the best reliability. This engine was actually running a PowderExplosionCoefficient of 0.0666 which is almost 4x more energetic than the fuel used for the Scotch Yoke engine at 0.01666, and has an IgnitionCoefficient of 0.0005555 which is 11% more volatile than the Scotch Yoke's 0.0005. The 2 stroke engine is thus running a fuel probably around 6-7x more volatile than the Scotch Yoke, and the higher compression ratio (5:1) of the Two Stroke vs the Scotch Yoke (3:1) means this little engine is probably extracting 10x as much work from a given volume of Powder than the Scotch Yoke engine.
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