I have a road bike I use for commuting and I'm about to move 20km further out, so I'm considering fitting a tiny engine to it to assist my ride to work.

However, where I live I have a restriction - the maximum power allowed is 200 watts (about 1/4 HP).

I've seen some kits, but they have huge engines (beats me why they have to be so big).

Further, I'd prefer a diesel engine (no spark/glow plugs) and better economy.

Some brief research has shown that a tiny (5cc or so) diesel engine should be able to produce about 200 watts. A larger one could be de-tuned. There are model aircraft diesel engines of this size, but they're quite expensive.

I've been told a "brushcutter motor" (small two-stroke) could be an option, but they are noisy, smoky and smelly.

I'm not worried about how to deliver the power to the wheel - I'm trying to pick the power plant first then make it work.

Has anyone got any suggestions for:

• diesel engine
• very small (200 watts max)
• not expensive

###Edit: My bike is a [Focus Planet TR 2.0 (2012)][2], which has [internal hub gears][3], so the solution can't involve replacing the hub.

Regarding range, I will live about 30km away from my CBD and batteries seems to have about a 60km range. Also, recharging takes a while, but filling a tiny tank takes seconds.

Also, I seriously doubt that the pollution created by a tiny 1cc engine exceeds that pollution created by the recharging process of burning coal and pushing the electricity through all the transformers and switches between the power station turbines and a bike battery.

For these reasons, I'm still seeking an internal combustion solution.