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Duel CNG/Diesel Fuel Engines
Continuing my thoughts on alternative fuel as it relates to running Fuel Cells to recharge batteries when boondocking I have thought a lot of running CNG (Compressed Natural Gas) for passenger vehicles. Getting more practical as the days go on. But the truck industry has begun to embrace running Duel Fuel Deisel engines. Some are running straight CNG for trucks that return home at night and can be refuelled easily and then there are more companies running duel systems for OTR trucks. I have posted a link giving some of the advantages of CNG/Diesel with big engines, and now it seems that they are close with a conversion for a Detroit Series 60. This might not be good for everyone but the cost of CNG on an equivelant basis is about $2.25 GGE vs. Diesel at $3.78. CNG runs cleaner and is better for the engine.
http://phillycleancities.org/wp-content/uploads/2012/03/ecodual.pdf
These two links might give someone a thought about CNG/Diesel as a duel fuel future.
Cheers
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5 Replies
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In some areas the cost of CNG is $1.79/gge; like Kwik-Trip in Wisconsin. The cost is even less if you have your own compressor and can brew your own directly from the gas company.
A gge … gas gallon equivalent is not really the same as a gallon of gasoline. The truckers I’ve talked to who are running CNG rigs tell me that a gge of CNG provides between 85% and 90% of the energy that a gallon of diesel (or they think gasoline provides).
Kwik-Trip in Wisconsin has 30 stations with CNG today in their 400+ station system. All its new trucks/tractors are CNG, diesel/CNG, or even LNG. They don’t plan on buying another straight diesel in the foreseeable future.
It appears the smaller diesel engines (up to 325/350hp) are being converted to straight CNG. I stood next to a Cummins in a Kwik-Trip tractor two years ago. Injectors replaced with spark plugs and CNG introduced via throttle body injection were the nighlighted changes to the Cummins engine. The hood was tilted forward, the engine was running, the K-T fleet manager and I carried on a conversion standing by the front tire without shouting at each other; very quiet. He said the drivers like the quiet engine, the automatic transmission, and the fact that CNG is domestically sourced.
The bigger engines (400 and 500 and more hp) use a blend of CNG and diesel. Sounds like a traditional diesel.
There are a number of hills the K-T trucks must climb leaving the K-T plants and warehouses in La Crosse (WI) which is just a few feet above the Mississippi River. The fleet manager conceded that their tests showed the CNG engine couldn’t maintain the same speed as a similar sized straight diesel, but the dropoff wasn’t insurmountable. (Mr. Mark should make a note of this.)
The K-T shop foreman said they have had to occasion to open up a CNG engine after considerable miles and they are stunned at how clean the inside is. Same for the oil at oil change, looks clean. The secret being little or no carbon atoms in the CNG, mostly hydrogen with burns clean.
The #1 obstacle to using CNG for buses like ours is where to put the CNG. The current generation of tanks are cylindrical with rounded ends which aren’t conductive to our bays and they are heavy. At 3600psi the range would be limited. The next generation tanks are expected to not have restrictions on shape which would make them more conducive for buses and they are expected to handle 4500psi to 4800psi.
I think CNG and probably LNG are great for trucks, buses, and trains that put on lots of miles. I don’t see NG as being conducive for our motor coaches. At the end of the day, a gallon of diesel (or gasoline) has a ton of BTUs and is avaiable just about everywhere!
Where CNG and LNG will help us diesel users is by decreasing demand for diesel as CNG and LNG picks up in popularity.
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Thanks for your post, an excellent insight into the technology from a practical usage. Thanks
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They no longer have diesel engines if they require spark plugs. Diesel engines initiate the combustion cycle with high compression, whereas if a spark plug is required the compression is insufficient to create combusiton.
That is the reason for the sound level difference.
As to power, BTUs are BTUs. In other words it is the BTU content of the fuel that is going to dictate perfromance. If a gallon of diesel contains 130 BTU (just a guess) and bio-diesel contains 110 BTU per gallon then the engine run on pure diesel is going to pull a hill better or get better MPG than the bio-diesel.
So far, despite all the presumed benefits to mankind and the environment, good old fashioned diesel fuel is still king. It may not burn as clean, or keep the engine as clean, but it gives more bang for the buck than anything else out there that is readily available, or that is practical for installation in our coaches.
By good old fashioned diesel I mean the stuff we used to burn before the regulators started forcing changes to the content such as reduction in sulfur levels.
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Dick,
Note taken.
Mark
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Jon makes good points.
As it was explained to me, the CNG/diesel combo engine don’t have spark plugs, start out with a heavy percentage of diesel (maybe 100%) and as they warm up CNG is introduced. Then depending on the load and speed of the engine the diesel/CNG split is varied. The CNG uses the explosion of the diesel to ignite as I recall. I can’t rmember how the CNG is introduced into the combustion chamber.
The straight CNG engine works just like a gasoline engine with spark plugs, ignition packs, and throttle body injection of the CNG. From what the Cummins rep told me, the engines used for both CNG and CNG/diesel combo were basically the traditional diesel blocks, rotating assemblies, valve train, and accessories.
Jon is right about BTUs. That is what gets the job done for the engine. One of the things I’ve learned about all of this is that the current definition for “gas gallon equivlaent” (GGE/gge) of CNG (which is how its sold) is that in practice its a little “light” compared to gasoline and diesel. I believe there is a “diesel gallon equivalent” (DGE/dge) defnition to, which is probably off a touch in definition of BTUs too. Maybe CNG and LNG will eventually be sold by DGE rather than GGE.
I can’t emphasis enough Jon’s final point about diesel (and gasoline for that matter) being hard to beat as a fuel source. Can be easily stored at atmospheric pressure, available and operates over a wide range of temperature, lots of BTUs per gallon at atmospheric pressure, easy to transport and transfer, etc.
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