It's a relatively simply process, but it's relatively complicated in that it costs us $200 million to get there. It's an injector that has two nozzles. Importantly, a diesel engine doesn't use a spark plug; it uses compression ignition. It compresses the air and then injects fuel and the fuel auto-ignites. Natural gas doesn't have the same ignition properties as diesel, so we need to use a small amount of diesel right at the end of the compression stroke to ignite that fuel and get the flame effectively started in the combustion chamber, and then we inject natural gas. We use between 1% and 6% or 7% diesel, depending on the duty cycle of the vehicle. It's a pretty constant injection of diesel on every combustion cycle, but the natural gas varies according to the power load of the engine.
On May 15th, 2012. See this statement in context.