Cummins using Natural Gas for Fuel

[Alan Reagan]

But how would the methane be injected in the Cummins? If it was put in through the air intake, the mixture not be precise. Also, there would be the risk of an explosion if the grid heaters turned on.

 

[jponder]

You talking about on our trucks? When they do Butane injection where does it go? It must go through the intake. I dont think the grid heaters are hot enough to ignite it. You thinking about going CNG ALAN? Heck go butane, its a liquid in the tank so as it boils out it will be cool and help cool the charge

 

[jponder]

or if butane is too heavy for you then go PROPANE!

 

[RustyJC]

Originally posted by Alan Reagan

If it was put in through the air intake, the mixture not be precise. Also, there would be the risk of an explosion if the grid heaters turned on.

2 of many reasons I don't like propane injection!



JMHO



As to the Cummins engines in question, they may be spark gas engines. A spark gas version of the ISB is available as a gas compressor driver - see HERE, or better yet, HERE.



Rusty

 

[Alan Reagan]

Just curious, John. With methane, I want to know how they get it in there in these trucks here in Savannah. When it's shipped, the LNG is near cryogenic. But even then, it has a very low vapor pressure..... only three to four psi. And it's kinda unpredictable as to how it's going to "boil off". Variables including atmospheric pressure and temperature are critical to a sustained vapor pressure .

 

[tgbol]

The Cummins LPG engines are really spark fired. They use elctronic injectors to fuel the engine and a spark plug to fire the mixture. Cat has a pilot fired system.

 

[jponder]

Originally posted by Alan Reagan

But how would the methane be injected in the Cummins? If it was put in through the air intake, the mixture not be precise. Also, there would be the risk of an explosion if the grid heaters turned on.

Are you talking on OUR trucks or on the buses???? If your talking about the buses how do you know they have a grid heater and they probably have a way to meter it.



If your talking about our trucks THE JUST DO IT and quite being skeered

 

[Alan Reagan]

Thanks tgbol. I wasn't sure if they were pilot fired or not. So the injectors are compressed gas injectors, I assume.



I Ain't Skeered :--) . Just a little nervous around things that go boom.

 

[JPope]

"... 2 of many reasons I don't like propane injection!... "



"... Just a little nervous around things that go boom... "



Sort of like the saying about pilots, there are old pilots and there are bold pilots, but no old bold pilots!!!!



Quite an education with this topic!!!!!

 

[jponder]

Originally posted by Alan Reagan

Just curious, John. With methane, I want to know how they get it in there in these trucks here in Savannah. When it's shipped, the LNG is near cryogenic. But even then, it has a very low vapor pressure..... only three to four psi. And it's kinda unpredictable as to how it's going to "boil off". Variables including atmospheric pressure and temperature are critical to a sustained vapor pressure .

Alan I didnt notice this post before. I wouldnt have guessed Natural Gas would be transfered as a liquid, Critical temp is -118 F deg and critical pressure is close to 700 psi. I dont see the point. I would have guessed it would be transfered as a compressed gas. The gas would be pumped into the busses tank. I bet they need some big tanks. Are you sure they are transferring the Methane as a liquid? WHY? I wish I hade a phse chart for Methane. if it has 700 psi at -118 you are going to have to get it REAL COLD till you get vapor pressures of 3 to 4 psi and why in the heck would they want tose low of VP's This is ver interesting

 

[jponder]

oh I forgot to mention, Vapor pressure wont be affected by atmospheric pressure, its a function of temp. The phase the Methane stays in will certainly be a function of atmospheric

 

[Alan Reagan]

Liquified Natural Gas is how it is received here from Trinidad. Vapor pressures in the tank are 3-4 psi both on the ship and in the storage facility. Now if there were a catastrophic release, it just spreads rapidly displacing all the oxygen when it is in this form. As it warms, it returns to its gaseous state and dissipates. To put it through the pipeline, it is in the gas state. You are correct, the transfer to vehicles is in the gas state. When I said "how they get it in there in these trucks" I was asking how the gas is injected into the engine, not put in the tank. I realize that the tank is carrying the methane in its gas state. I'm unfamiliar with what pressure a gas injector would pop off at.



The 700 psi you are referring to is probably the compressed gas pressure. The vapor pressure I'm referring to is the boil off gas being released from the liquid as it warms. I don't remember the exact temp but I believe the liquid state is around -400*.

 

[jponder]

I had no idea we imported Natural Gas into the USA. I would love to see one of those ships.

 

[JohnE]

Cummins natural gas or "alternative fuel" engines are commonly available in B Gas + & C Gas + packages.



I work at New Flyer. We produced most of the natural gas transit buses in service around North America including those at MARTA (Atlanta).



A Cummins natural gas engine uses a B or C series block with different pistons and head to accomodate spark plugs. Pistons are for spark ignition and result in approximately 10. 5:1 compression ratio.

A Woodward mixer (carburetor) meters the natural gas at around 75 psi based on throttle position, turbo boost, exhaust back pressure, knock sensors, and engine temperature. No direct injection.

They are not a pilot injection engine as those commonly use at co-generation facilities.



We use only C series engine rated from 250 to 280 hp. Torque is around 1000 ft-lbs from these engines.



No grid heaters on these engines. FMVS does require a complex fire & gas (leak) detection system with integral suppression system.



The turbo is a HX-40? with a coolant jacket due to the higher exhaust temperature of a spark ignition engine. After treatment usually includes a catalyzed muffler.



Transit buses use either Liquified Naural Gas (LNG) or Compressed natural Gas (CNG) for storage. CNG is the most common storage. Depending on the bus size this usually ranges from 4 to 7 tanks.



Maximum tank service pressure is 3,600 psi. A primary regulator drops the tank pressure down to around 100 psi. The primary regulator has a water jacket to prevent freeze up from the gas expansion.



Tank fill is from hot (direct) fill from a pump, cascade (storage tanks) or a combination of the two. MARTA uses Cat Diesel engine powered pumps for a very fast and hot fill.



Our tanks are all burst tested to 9000 psi and very stout.

Free naural gas is very difficult to ingite and sustain. Diesel is very low too. Gasoline is one of the most easily ignited vapors so what do most vehicles on the road use for fuels?





Cummins/Westport is working on direct injection engines. Rumor says it will be a dual injector with diesel pilot and gas.



Import natural gas? Most of our (local area) gas comes from Canada by pipeline.



If you have more quesions fire away.



-John

 

[A Johnson]

John, good post.



www.westport.com

www.cumminswestport.com



A Johnson

 

[DJW]

On a visit to New Zealand, country population 3 1/2 million, at a self service gas station in the suburb of Auckland, the choice of fuel was, Petrol, (Gasoline) Propane or Natural gas. In 1939 at age 13 in school in Wales UK, took Liquifycation? of Air, plus separating Gasses different temperatures etc, quite interesting. This Gas Station was for use of the general public, and certainly was not a Truck Fueling Station. One wonders if Standard Oil is still calling the Shots here in the USA ?

 

[Alan Reagan]

Excellent post, John on how the engines work. So it is carbuerated. That's what I was curious about.



jponder, I have a couple of pictures but they are too big too attach (477 kB). It's some I took last year of an inbound tanker.

 

[jponder]

John you mentioned that some buses used LNG?



If you fill a tank with cold NG,if you wanted to to keep it a liquid, then do the buses have a system to keep it cold?



If you dont keep it cold then the prsessure is going to keep rising and rising.



What do they do if the bus sits overnight with a full tank, OTOH maybe 9K psi cylinders can handle it. Makes you wonder what the pressure could reach at say 100 degress F. Mehtane will not form a liquid at those high pressure so the tanks better be stout... ... . It sounds like they are

 

[JohnE]

Thanks "A" for adding the links.

Originally posted by Alan Reagan

Excellent post, John on how the engines work. So it is carbuerated. That's what I was curious about.

...

Here's the one for Woodward mixers

I call it a carburetor simply because it uses a butterfly valve same as any gasoline powered vehicle.

Originally posted by jponder

John you mentioned that some buses used LNG?



If you fill a tank with cold NG,if you wanted to to keep it a liquid, then do the buses have a system to keep it cold?



If you dont keep it cold then the prsessure is going to keep rising and rising.



What do they do if the bus sits overnight with a full tank, OTOH maybe 9K psi cylinders can handle it. Makes you wonder what the pressure could reach at say 100 degress F. Mehtane will not form a liquid at those high pressure so the tanks better be stout... ... . It sounds like they are

I'm not very knowledgable on LNG storage. I do know it requires SS insulated tanks to keep the fuel in cryogenic (liguid) state. They do not have refrigeration not do I remember the burst pressure. Most transit companies use LNG because it comes without mercapton (stink). CNG filling sites are in many residential neighborhoods and causes complaints from odor.



Methane or natural gas will go cryogenic if filling an empty tank from a high pressure cascade (storage tank) system. (Remember I said the primary regualtor has a water jacket to freeze up?) Composite tanks are not tolerant of cryo flow. They are 100% designed for CNG only. Yes they are very stout. The most dangerous part of CNG is the C or compressed. Natural gas in free state is very difficult to sustain combustion.

We have a very strict chart on pressure fills based on ambient temperature. This prevent Pressure Relief Valves (PRVs) from discharging if the temperature rises suddenly. Buses leaving on a route can take a full fill as they burn down the pressure quickly.

 

[jponder]

Cool, Now the next step... ... ..... HYDROGEN! That would have even lower emissions. and we could make it via solar energy. Just because they want to use H2 in those fuel cells shouldnt mean we cant run a little in our Cummins