The potential opportunities for fuel cost and emissions reduction as a result of converting from diesel to natural gas (NG) are well known in the rail industry. Recent developments in domestic sources for petroleum have both lowered the cost and stabilized the natural gas market making the adoption of NG more strategically viable than ever before. NG Engine conversion systems for medium speed diesel engines have been available for over 20 years and environmental incentives are helping to further support the adoption of NG not only as an alternate fuel, but possibly as the new primary fuel. The major challenge for railroad transition to NG is now to develop a manageable and cost effective on board storage architecture with capacity to provide sufficient range to meet industry acceptance for general use.
For long haul applications, the solution has been to add a large locomotive NG tender. For short line, switcher and commuter applications, the fuel cost benefits do not warrant the cost and complexity of such a system. For these short to medium range applications, an “on locomotive” storage system with a capacity equivalent to a minimum of 500 diesel gallons is a better solution. This paper summarizes the development of a crashworthy, high capacity, underframe NG storage solution packaged in the form factor normally occupied by the conventional locomotive diesel fuel tank (Fig. 1).
Primary challenges for the CNG storage system solution are to achieve high storage density and crashworthiness while within the confines of existing AAR M-1001Plate C profile. It is expected that the system is to meet both the CFR/FRA structural requirements for diesel tanks and relevant DOT requirements for CNG cylinders used in mobile applications.
The NG storage system presented consists of an outer enclosure which mounts to the locomotive similarly to the existing diesel fuel tank. The enclosure contains and interfaces with NG cylinders specifically designed for the application. The system design withstands the various load requirements defined in 49 CFR Part 238 Appendix D, that simulate both jackknife derailment and class 8 truck side impact scenarios. NG cylinders within the enclosure must be approved for use in this application and have sufficient capacity and maintainability to create new opportunities for NG conversion in the rail industry. The primary design goal for the storage system is to integrate the cylinder size and configuration within the enclosure such that storage volume is maximized and crash impact loads are minimized. Impact loads are distributed through the system ensuring that point loading sufficient to breach one or more of the NG cylinders or fuel lines does not occur. An overview of the development and results of physical derailment and side impact testing performed in support of this effort are presented.