Ok, so two-stroke diesels have the potential to produce twice the power of a 4 stroke. The concept of a diesel is that fuel is injected into the cylinder and the pressure is high enough to create combustion without a spark plug. Nitromethane has been used in drag racing for a number of years in engines similar in design to gasoline piston engines. One of the characteristics of Nitromethane is its tendancy to pre-ignite (create knock). Since it is so easy to detonate, why not create a small 2-stroke diesel engine that uses either pure Nitromethane or a mixture of nitro and diesel? Of course a small air compressor would be needed due to the two-stroke diesel design (see link). Perhaps in the 10 seconds between when you twist the throttle and crash into something, it would be quite interesting.-- acurafan07, Nov 15 2006 Glow plug engines http://selecthobbies.com/Two stroke piston engines that run at about 20.000 rpm, on methanol + nitromethane + castor oil [jmvw, Nov 15 2006] A Lightweight, V-4, Two-Stroke Diesel for Aviation http://www.greencar..._lightweight_v.html2 stroke diesels suitable for vehicles? [greyfiend, Aug 31 2007] Sounds like a Cox glow plug engine. No air compressor needed.-- jmvw, Nov 15 2006 don't you have lubricity problems trying to pump the fuel at such high pressures, ie does the nitromethane kill the fuel pump/can you make a fuel pump suitable for diesel engine injection that can pump nitromethane.
"Ok, so two-stroke diesels have the potential to produce twice the power of a 4 stroke"
um. yeah. not quite.-- Custardguts, Nov 15 2006 "This means that a two-stroke engine has the potential to produce twice as much power as a four-stroke engine of the same size." -howstuffworks.com-- acurafan07, Nov 15 2006 a gross oversimplification. That site is aimed at a very low level, and whilst being useful when looking around for an interesting article, I wouldn't cite it as a reference when trying to make an engineering claim.
I can't remember what the theoretical limit is for a two-stroke, I'd have to hunt out my textbooks again, but I know it wasn't double that of a fourstroke of the same displacement. At the very least, compression ratio and/or available oxidising atmosphere is limited in a two stroke.
I'll be waiting for the reference from wikipedia (which, whilst sometimes in error, is rather rarely so) or an engineering site.-- Custardguts, Nov 15 2006 Well wikipedia certianly doesn't mention 100%... so you're right maybe only 50-60% more. But, //available oxidising atmosphere is limited in a two stroke.// one of the benefits of bringing nitromethane into the equation is that it supplies its own oxygen.-- acurafan07, Nov 15 2006 Ah yes, but probably still not double the output of a four stroke running on nitromethane.
Lets not quibble.
Your idea is to have a small but hugely powerful engine running a scooter. I like that idea. If you bring enough ponies to the party, I'll bring the beer and skittles.
[+]-- Custardguts, Nov 15 2006 I've been researching this idea all day before I stumbled across this thread. Two stroke diesels are used as some of the biggest most efficient power plants... Two stroke glow engines(cox engine?) are used as the smallest, best power to weight ratio engines in model RC gear. Both are totally capable of running on bio-fuels (vege oil for diesels, methanol for cox engines)and have awsome power to weight ratios... I can't understand why aren't we seeing these power plants in sizes suitable for motorbikes or ATVs?-- greyfiend, Aug 31 2007 Okay, follow my grossly over simplified logic here: If a 49cc 2 stroke engine creates ~1 hp and can adequately power a scooter, then you can power a scooter with 1 hp. I’ve herd that some of the nitro engines used for powering RC cars can get up to being 2-3 hp. With the right transmission, wouldn’t it be possible to create a scooter powered by a RC style nitro engine?
As an added bonus, those engines are tiny and could be mounted to a foldable scooter frame, think gas powered razor scooter!
[+] fresh pastry-- evilpenguin, Aug 31 2007 Comparing 2-stroke to 4-stroke it is true that you can get twice the HP. The missing piece is that not all two strokes are the same.
All two strokes need some type of blower to force air into the cylinders. Small two strokes (Cox engines, weed wackers, etc.) use the crankcase pressure created by the piston motion to do this. This is why you need to mix oil with the fuel or in the case of Cox engines, they mix Castor Oil in the nitromethane to lubricate the lower end. This works but not as well as the real blowers used in big two stroke diesels (Detroit Diesel). The exhaust in little 2-strokes are handled by a cut out in the side of the piston bore. The exhaust in a big 2-stroke is handled by 2 or 4 poppet valves in the head. Small 2-strokes mix the air and the fuel as it goes in the engine and 2-strokes need intake air to blow out spent exhaust gases (scavenging), which leads to some unburned fuel going right into the exhaust. Big 2-strokes inject the fuel in directly and only after exhaust valve have long been closed.
The smallest big 2-stroke diesel I’ve seen was a 254 which is 2 cylinder engine of 54 cu. in. displacement each. They are heavy especially because of the roots type blowers and the mass of metal needed to contain the combustion pressures and handle the torque. It weighed over 300 lbs but got great “mileage” (they are installed in refer trailers or “small” generators.)
Nitromethane is wonderful stuff because gas/diesel need about 14:1 air/gas mixtures, Nitro is 1:1. So although nitro has only a quarter of the energy per gallon, you can use 14 times as much per displacement so you get 3.5 times the power. I mention this because you may now realize why we don’t drive to work on nitro, because a moped running nitro would get worse mileage than a Hummer. That not to say the moped wouldn’t be fun, it would, you just need a BIG fuel tank.-- MisterQED, Nov 29 2007 random, halfbakery