Lube-Tech
Beginning with the initial emissions standards signed by the EPA in December 1997, locomotive engines have been subject to a tiered system of increasingly stringent emissions standards, ranging from Tier 0 to Tier 4. Higher tier numbers are assigned to more recent and stricter emissions standards. Since 2015, the railway industry has been required to meet Tier 4 locomotive engine standards, which impose limits on particulate matter (PM), total hydrocarbon emissions (THC), NOx, and CO, as outlined in Table 1 [4].
Table 1: EPA emissions standards for line-Haul locomotives. HC standard refers to THC for diesel, non-methane hydrocarbons (NMHC) for natural gas, and THC equivalent (THCE) for ethanol engines [4].
To meet these standards, advancements in technology have been pursued in various areas, including advanced “stop-start” control systems and more efficient locomotive engines, aiming to enhance fuel efficiency and minimise engine idling times [3]. The European Commission is ruling out the strictest emission standards, which is tougher than Tier 4 [Figure 2].
PUBLISHED BY LUBE: THE EUROPEAN LUBRICANTS INDUSTRY MAGAZINE
No.148 page 2
The regulations are slightly different for switch locomo- tive emissions. According to Tier-4 regulation, switch locomotives are allowed to emit 2.4 g/bhp-hr CO [5].
Diesel engine lubrication
Being the heart of the locomotive, engine lubrication is extremely important for performance and emission control. Locomotive diesel engines typically generate between 1200 to 6000 HP. However, most of the Wabtec (formally known as GE) and Progress Rail (formally known as EMD) locomotive engines are rated at 4500 HP [6]. To keep such engines running smoothly at these horsepower levels, the engine oil must have the necessary qualities to lubricate the piston rings/liners, connecting rods, main bearings, and valve trains. The turbocharger bearings in locomotive engines are also lubricated by the engine oil. The engine oil serves multiple functions, including lubrication, cooling, and maintaining cleanliness by removing combustion byproducts, deposits, and debris. It also helps neutralise acidic combustion byproducts such as sulphuric and nitric acids. Engine oils typically contain an additive system that contains functional components that serve as detergents, dispersants, anti-wear agents, antioxidants, viscosity index improvers, and pour point depressants. These comprehensive additive systems are formulated in the oil to enhance performance and extend oil drain intervals, where applicable.
Figure 2: Comparison of PM and NOx emission limits between the U.S. and EU [4].
Typically, the primary anti-wear component found in most motor oils is Zinc Dithio Diphosphate (ZDDP). However, railway engine oils have traditionally been formulated without zinc due to concerns about potential damage to silver wrist-pin bearings used in Progress Rail engines. In contrast, Wabtec engines did not utilise silver bearings and, therefore, did not require zinc-free oils. To ensure operational simplicity and avoid the need to manage different engine oils for a mixed fleet of EMD and Wabtec locomotives, the industry adopted zinc-free oil as the engine oil standard. Although EMD ceased the use of silver
32 LUBE MAGAZINE NO.177 OCTOBER 2023
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