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Finished reading an article in November Trains magazine referencing that BNSF and CN are evaluating running some engines on compressed or liquefied natural gases.  Given the lower gas fuel cost vs diesel, these RR are taking a second look at possible fleet conversion.

 

I assume the diesel motors are extensively modified to accept these gases.  My understanding is diesel fuel has a high ignition point requiring great compression to generate the heat to combust the fuel, while gas has low ignition point thus lower compression required(or maybe I have ignition points reversed, but you get the idea).  I haven't found any material that explains how the RR modify the equipment for LNG.

 

Second in light of accidents, if a fuel tank ruptures usually there is a oil leak no fire.  But if one of the gas fuel tenders ruptured, there would be a rather cataclysmic explosion.  I have to assume that tanks are double lined heavier steel to minimize punctures.

Last edited by rrman
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After googling around, stumbled onto this simple explanation that seems to answer my technical questions.

 

http://www.afsglobal.com/faq/d...-gas-conversion.html

 

Alot of work it seems, but guess bean counters have crunched the numbers to justify the labor and material costs to change over.

 

Still haven't found an explanation for fuel tenders safety, though.

Last edited by rrman
Originally Posted by rrman:

I assume the diesel motors are extensively modified to accept these gases.  My understanding is diesel fuel has a high ignition point requiring great compression to generate the heat to combust the fuel, while gas has low ignition point thus lower compression required(or maybe I have ignition points reversed, but you get the idea).  I haven't found any material that explains how the RR modify the equipment for LNG.

 

CNG and Propane conversions are popular for diesel pickups. Basically they are injecting CNG/Propane through the air intake before the turbocharger where it mixes with the incoming air. The better conversion kits add CNG/Propane and back off on the diesel fuel for fuel economy purposes (sometimes the kits are added to make additional power). Diesel fuel is still burned to ignite the CNG/Propane. I think Propane has a tendency to detonate (pre-ignite) due to its lower octane rating than CNG (~110 vs. ~130). LNG is stored at ~-260*F and when heated becomes natural gas. You can get a good idea of whats involved in the conversions by googling CNG or Propane conversion kits.

I work with a lot of reciprocating-piston distributed power generators in the 1200 - 6000 HP range and there are a lot of them now being made to run on natural gas.  It is a fairly straightforward re-design, and there are even dual fuel units available, but they are expensive and higher maintenance.  

 

The trend to NG as fuel instead of diesel originally started due to compliance with emissions requirements - in some jurisdictions it is  easier to get a unit certified if it burns NG than diesel.  Cost is now another issue accelerating the trend.  Also, many fast-start diesel back-up units (designed to fire up and produce power within 7 seconds) will use NG to start, because when running on that they can fire on the first compression stroke - they then transition over the diesel with a few seconds.

 

It will be interesting to see if the RRs follow this route.  NG-fired units have proven to be slightly lower in maintenance costs over time, so there may be yet another reasons. 

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