Here is the short version.  In the early part of the last century, a British company (Lister) built some stationary diesel engines intended for agricultural and light industial use.  They turned out to be very dependable, durable and economical.  Some of the spare parts were made in India.  The brits finally quit making the engine in the 1980's I think, but the Indians kept on making parts and then whole copies, some better and some worse.  

But every type of engine in the world has some compromise built in.  For Listers, it's weight.  My six horsepower Lister copy (listeroid) weighs around 700 pounds.  It has the same output as my 40 pound lawn mower.  

The difference is the typical lawn mower engine is rated around 700 hours operation before needing an overhaul.  The Lister is rated 50-100,000 hours between overhauls.  Plus, the fuel economy on the efficient Lister design is probably double that of the gas burner.  Plus, it can be made to burn used crankcase oil, or used vegetable oil from fryers, etc.

Here's a picture:

Good luck and have fun!