LNG will probably replace much of the diesel fuel used by railroads in North America in the next decade. At one time, I thought that maybe they would go electric but the low cost of LNG will probably preclude that in the near term. I know that Caterpillar which owns Electro-Motive Diesel has a joint venture with Westport Innovations for LNG/disel injectors. GE is also working on using LNG in their locomotives.

Power engineers have known for nearly a hundred years that diesel engines can have natural gas mixed into the input air of the engine to reduce the consumption of diesel fuel. This can be done with propane and butane as well and many diesel emergency generators run on natural gas when available with a small amount of diesel injected to "spark" the methane into combustion. Only very high compression, free piston engines can ignite methane with compression ignition. Naturally methane can be used in the intake air of gasoline engines with or without gasoline. With a slight reprogramming of the engine computers most diesel locomotives would operate tomorrow partially on propane from a trailing tanker car at much less cost. ..HG..

Henry,

You are correct and this is how most diesel engines run on natural gas. They carburet or inject natural gas into the air intake and ignite the more or less homogeneous mixture with a small diesel pilot injection. However, Westport Innovations has a dual fuel injector that injects both natural gas and a small amount of diesel for ignition. This allows the engine to run as a true diesel with a non-homogeneous mixture. They will also run on all diesel.