[quote=“kamiwaza”]
That’s not true. Honda in particular put very large amounts of money into 2-stroke research. Both 4- and 2-stroke technology has come a long way, but currently 2-stroke engines are not efficient beyond about 500cc.
[/quote]
Um, yeah. Here’s a little two-stroke engine for you: Up to 14 cylinders, displacement: 25,480 liters. The one in the photo is ‘just’ a baby 8-cyl version. By far the most efficient internal combustion engines ever built are two-strokes, and most are more like 20 liters in capacity than 500cc. Look at the 10-cyl gas engines used for pumping natural gas, marine diesels, diesel-electric locomotive units… all way more efficient than four-strokes in similar power ranges. This is what I mean, people are not thinking beyond the simple crankcase compression, piston-ported, gasoline-burning, spark-ignited norm. Yes Honda has done some research into sparkless ignition and alternative combustion processes, but beyond that, nothing. If you want to see the cutting edge in two-stroke tech you need to be looking at turbo-diesels, opposed-piston units, uniflow engines, turbo-compounding etc. With the advent of low-sulfur diesel, biodiesel, electronic fuel injection and advances in turbocharger design there is more to come.
2-stroke TDi heavy hauler
2-stroke TDi aero engine
108,000hp container ship two-stroke diesel
Hydrogen-burning pivotal-piston two-stroke
MAN 79,000kW 2-stroke diesel generator
The problem long associated with the two-stroke is pollution and poor fuel economy. This is mostly from simple piston-ported design and the fact that the intake and exhaust port timings overlap, allowing a gasoline/air mixture to pass straight into the exhaust unburned. Using crankcase compression for cylinder filling means that total-loss lubrication is necessary, there’s no way to recycle the engine oil. A diesel cylinder sees no fuel until combustion starts, so no fuel can escape the fire. Pollution levels are therefore the same as a four-stroke. Use of a turbo or supercharger obviates the need for oil mist lubrication and a conventional four-stroke type lubrication system can be used. Hell, one of the most exquisite engines ever built (in the 50’s) was a 41 liter afterburning two-stroke turbo diesel with turbochargers mechanically linked to the crankshaft to divert unused energy from the turbines back into the drivetrain (Napier Nomad).
It’s been said many times that the average motor vehicle consumer is one of the most stubborn sonofabitches on the planet when it comes to real innovation. They go along with some minor changes in engine technology, but take away the basics of camshafts and valves or the four-stroke cycle and they will have none of it. It’s the industrial users that are brave enough to try new ideas.
