I have to say that I too looked for small diesel engines and the smallest one I could come up with was the Hatz 1B20. It's a 4.6hp, 243cc diesel that weighs in at about 50 pounds. Northern Tool sells them for quite a hefty price. Not worth it IMO.
Diesel engines are heavy,expensive to build,and difficult to start,with a 20 to one or so compression ratio,they need a glow plug to get going or a blow torch.What they have going for them is low specific fuel consumption.Absolutely the last engine any person,not looking for punishment&frustration would think of putting on a bicycle.
diesel is almost $4.50 a gallon here, im not sure it would be worth the diesel conversion, would be very different though, i bet if someplace makes a 50cc diesel, it would get really good mileage though.
1) Have a lot of TQ without having to rev the snot out of them
2) Great MPG. Should be able to hit the 250+ MPG mark
3) I would put money on it that you could get 5 HP out of a small 50cc diesel. That doesn't seem like much but regular gas engines make around 2.1 to 2.5 hp. That is a big increase.
4) Should be great for hills
5) Should last a long time
You pay a little more for diesel but do the math........is it really that much more out of pocket for the fuel when we are talking about a 50cc engine that would get over 200mpg.
Assume 4 for regular and 4.50 for diesel. Lets also assume that the bikes get the same mpg (around 200 miles).......diesel should get better mpg but for sake of arguement we'll say the same.
4/200 = .02 ............that's 2 cents per mile
4.50/200 = .022 ........that's 2.225 cents per mile.
So your complaining about paying an extra .225 cents per mile?
Eat one less cheesburger at McDonalds and you'll make your cost up in fuel for the year. Now let me run another thing past you. What if you could run your cooking oil in the engine. Eat fries for lunch and use your own used oil for your engine. ie almost never having to fill up at the station. If you couldn't burn straight cooking oil I bet a dozen donuts that you could mix the oil with diesel to make it go further. But we are talking about less than 3 tenths of a cent per mile here.
The big down side is that buying the engine to start off with would be more. However diesel engines tend to last longer due to the engineering that goes into them.
If gas goes to (when gas goes to) 5 or 6 bucks a gallon we will see these engines developed and I want to be the one investing in this company that will make these engines.
Biodiesel would be the only reason I'd be interested in a micro-diesel. If you look at this thread, you'll see a post in there by ducatiluke about an 18cc diesel that's currently being developed. Their primary goal is to make a durable engine for irrigation pumps, but they're also aware of it's other potential applications.
It's VERY small, and could probably be adapted to a bike pretty easily.