Have just read a newspaper story. Here is a few lines from the story. Can anyone explain to me how a LNG 'diesel' engine works? See the last line of the story.

Cummins Westport gets gas engine order from China

VANCOUVER — Cummins Westport Inc. has received its first low-emission engine order for Beijing's bus system, the company announced today.
Beijing Public Transportation Corporation has ordered 75 buses powered by the company's liquefied natural gas engine.
Beijing Public Transportation is Cummins Westport's largest customer in Asia, with more than 2,000 natural gas engines in bus service.
It is the second-largest order to date for the two-year-old joint venture between Cummins Inc. and Vancouver-based Westport Innovations Inc. The company markets technology that allows diesel engines to user cleaner-burning natural gas.

 

Stan, the Cummins NG engines that I have seen, used for power generation and such, are built on the same basic engine, but with different fuel delivery. They are almost the same as their diesel brothers but not running on diesel fuel. It is a conversion.

 

Are they still a compression ignition engine? Or do the have spark plugs? If it is compression igniton how is the gas injected?

 

All the ones I have seen did have spark plugs, these were on 1500kw gen sets. Different heads on these guys. Seems like the diesel sets had better power, but I rekon they want the cleaner emissions.

 

Kinda figured the media had it wrong. Just could not get my mind around a diesel LNG engine. Diesel yes. LNG yes, but not diesel LNG

 

There is such a thing as a diesel/natural gas engine. The natural gas is introduced into the engine intake air by a regulator. The "blend" is burned by the engine. I have seen many fleet vehicles that run this way. Most have a cylinder of "Compressed" Natural Gas.

LNG (-260F) is very cold like liquid nitrogen. My guess would be that the liquid is run through an ambient vaporizer and then to the regulator that would then blend it with the intake air. The vaporization of the liquid would produce a high pressure at the regulator for efficient blending with the regulator. The industry is moving toward the LNG due to the amount of fuel that is able to be carried. The Compressed NG system only have an effective range of maybe a couple of hundred miles. The Liquid allows for a much larger amount of fuel to be stored in the same space. One cubic foot of Liquid NG is equal to 600 cubic feet of vapor.

The introduction of NG into the diesel charge is supposed to reduce emmission and provide the same or improved power.

 

Thanks 4X4 for the explanation. Are you saying that these engines are still a compression ignition engine? Does that mean the these engines have no spark plugs, no injector pumps and no injectors?

 

Transportation engines must be miles ahead of the power generators. Or could these combo engines be limited by size?

 

I'm not absolutley sure how Cummins/Westport handles their LNG conversions. Cat/Clean Air Partners has a LNG/CNG conversion. It uses pilot injection of diesel fuel to "spark" the LNG or CNG. The ratio is typically 85/15. The benefit is that there is just enough diesel fuel injected to start the burn, but if the truck runs out of "gas" away from a refueling center it can be operated conventionally on 100% diesel fuel. There is no change in engine operation other than the reduced power caused by the lack of equivilent BTUs. Also known as Duel Fuel engines.

 

http://www.cumminswestport.com/index.php has the all the info on how it works. Basically they have both types, spark ingnited and pilot ignited.

 

TPyle got it right. His comments cover the type of engines that I had in mind.

 

I believe diesel is used for the pilot injection, and LNG is used for the main shot. It is a special injector that westport has manufactured that makes the engine run on diesel and LNG So... It is still a compression ignition engine.

Edited to add: Sorry tpyle I just read your post more closley...

 

Thanks guys for all tour info on this. Learn something new every day. Now, if I could only learn how to remember what I learn ......

 

Yesterday, I recieved the new Diesel Progress. Seems as though Cummins will also be offering the Cummins B propane to the FCC (Freightliner Custom Chassis) for various vehicles.