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Verified Technologies for SmartWay and Clean Diesel

Caterpillar Technology—Locomotive Selective Catalytic Reduction (SCR) System

This retrofit technology is included on EPA's Verified Technologies List for Clean Diesel.

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Technology specifications

Engine Model/Application

Caterpillar 3516, line-haul locomotive engines; either originally manufactured to meet Tier 2 standards for model years 2010–2011, remanufactured to meet Tier 1 standards for model years 2012–2013, or remanufactured to meet Tier 2 standards for model year 2016; turbocharged with power ratings 2650 ≤ Horsepower ≤ 3005 when used in line-haul application/duty cycle only

Retrofit Fuel, Max Sulfur 15 parts per million (ppm)
Reduction in particulate matter (PM) 20%
Reduction in nitrogen oxide (NOx) 75%
Reduction in hydrocarbons (HC) 90%
Reduction in carbon monoxide (CO) 70%

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Criteria to achieve emission reductions

The following criteria must be met in order for appropriately retrofitted engines to achieve the aforementioned emission reductions:

  1. The Caterpillar Locomotive SCR System is appropriately installed and operated in a line-haul locomotive application.  Emission reductions are not verified for locomotives operated in switcher applications or switcher duty cycles.
  2. The locomotive must be operated on ultra-low sulfur diesel fuel (ULSD) of 15 ppm or less.
  3. The locomotive must always have a supply of Diesel Exhaust Fluid (DEF) that meets and displays certification of the American Petroleum Institute ISO Standard 22241-1 quality requirements that ensures the proper purity and concentration of 32.5% of urea. The engines and locomotives must be designed to track and log, in nonvolatile computer memory1, all incidents of engine operation with inadequate DEF injection or DEF quality.
  4. The SCR system shall not be sold or operated in geographic areas where the DEF may freeze (-11°C), unless it is equipped with tank heaters and DEF line heaters to prevent freezing. 
  5. Caterpillar is required to provide the operator with clear and visible instructions for maintaining DEF for proper system operation.
  6. Each installation will be equipped with a monitoring system that displays warning lights visible to the operator and audible alarms for low DEF tank level, high SCR inlet temperature and system abnormalities. The monitoring system will also store diagnostic error codes related to DEF tank level and system malfunctions.
  7. The engine exhaust temperature must achieve at least 240°C for 40% of operation and not exceed 550°C. Caterpillar will review actual locomotive operating conditions and perform temperature data-logging prior to retrofitting a locomotive with the Caterpillar Locomotive SCR System to ensure compatibility.
  8. The Caterpillar Locomotive SCR System may require replacement if SCR inlet temperature exceeds 550°C for an extended, continuous period of time. Operation with temperatures above 550°C may require inspection for damage by Caterpillar.
  9. The Caterpillar Locomotive SCR catalyst should be replaced after 15,000 hours of operation or when the locomotive is rebuilt/remanufactured, whichever comes first.
  10. Caterpillar is responsible for informing customers, in writing, that disposal of the Caterpillar Locomotive SCR System must be in accordance to all applicable federal, state, and local laws. 

1  Non-volatile storage is computer memory that can retain stored information even when not powered.

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Verification Letters from EPA

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