KiwiRail’s new DM class locomotives for the South Island

Historically, New Zealand acquired locomotives for the national railway network from English builders in the 19th century, followed by a swing in favour of American builders, then proceeding to establish its purpose-built workshops to build steam locomotives and rolling stock, as well as utilising several local engineering firms.  The introduction of electric traction in 1923 for the Otira Tunnel saw English-Electric selected as the builder of the EO class, continuing with the EC class for the Christchurch-Lyttelton electrification in 1929 and again for the Wellington suburban service in the mid-1930s (ED and EW classes), followed by the DM/D electric multiple units (EMUs).

Fast-forward to the phasing out of steam traction in the 1950s in favour of diesel, the Government again turned to English-electric for its first main-line locomotives – DE, DF and DG/DH classes.  The double-cab DFs were expected to establish a fast 12-hour freight schedule between Auckland and Wellington, but did not live up to expectations and were subsequently transferred to the Frankton-Bay of Plenty line to see out their days; the half-units (DG/DH) were used in both islands, but at a mere 750 horsepower, encountered increasing difficulty with heavier freight trains on the mountainous sections of our main lines, and could not achieve the same speeds as the steam-powered JA class on the South Island Limited (70+ miles per hour) which they were intended to replace.

Consequently, for the North Island, New Zealand Rail Limited (NZR) turned to American builder General Motors (Electro-Motive Division) in the mid-1950s for the 1,400 hp DA class for the North Island Main Trunk (NIMT) to replace the KA class 4-8-4’s, along with the smaller, lighter variant DB class for secondary lines. These were followed by the new EMD-DF class from its Ontario plant, which is still in service today in both islands. The South Island had to “soldier on” with older diesel classes (and steam) until 1968, when NZR turned to Japan to build a new type of diesel-electric locomotive for the South Island, incorporating a high-revving Caterpillar engine built by Mitsubishi Heavy Industries; they were the last “whole fleet replacement” for “The Mainland”.

Subsequently, NZR turned to a new American builder (General Electric) to supplement the DA class with a more powerful type developing 2,750 hp (DX class). These came online in 1972, all North Island-based. In 1988, with the completion of the NIMT 25KvA electrification between Te Rapa and Palmerston North, Brush Traction was selected for the motive power, producing the smart EF class—at 3,000 hp, New Zealand’s most powerful locomotive at the time.

The final phase of North Island locomotive development to date is the Chinese-built DL class of diesel-electric introduced in 2010. These have had several “issues” since their introduction, so when it came to the South Island’s turn to upgrade its power, KiwiRail turned to European locomotive builders, selecting the tender of Swiss firm Stadler AG. KiwiRail created a functional specification from which Stadler has developed the design and tech specs. These are being built at its facility in Valencia, Spain, and will enter service in 2025.

However, the first two prototypes were unloaded from the heavy-lift cargo ship Eemslift Nadine at Lyttelton on 19 October 2024 and towed to Middleton Yard by DXs 5229 and 5108 for an intensive programme of commissioning and testing over the next six months. The next batch of five locos is virtually ready to be shipped, but this will not occur until after any “bugs” found with the prototypes have been ironed out. They’re expected to ship in June 2025.

Caterpillar engine – technical specifications

Caterpillar manufactures the Cat® C175-16 rail engines at its large engine facility in Lafayette, Indiana, USA. Depending on locomotive configuration, they produce between 2,800 kW (3,725 hp) and 3,000 kW (4,023 hp) at 1800 RPM, with peak torque from 1,500 RPM. The model designation C175-16 relates to a cylinder bore size of 175 millimetres and a configuration of 16 cylinders in a V format. Combined with a stroke of 220 millimetres, total engine displacement is 84.7 litres (5,168 cubic inches) or 5.29 litres per cylinder.

The Cat® C175-16 in the DM locomotive is a four-stroke diesel engine with a common rail fuel injection system with twin turbos, and includes a Selective Catalytic Reduction (SCR) exhaust after-treatment system. The engine uses Diesel Exhaust Fluid (DEF/AdBlue) injection and SCR catalyst to meet Euro-V emissions reduction levels.

Available in 16- and 20-cylinder configurations, Cat® C175 diesel engines are used across Caterpillar’s product lines in applications including power generation, mining trucks, locomotives, marine propulsion, and offshore drilling and production. In December 2023, Caterpillar celebrated the production of the 10,000th engine on the Cat® C175 platform, which has been used around the globe since 2009, logging more than 140 million operating hours across numerous industry sectors.

Environmental aspects

New Zealand passed its zero-carbon amendment to the Climate Change Response Act 2002 in 2019, which set a target for all greenhouse gases (except for biogenic methane) to reach net zero by 2050. This is in line with the Paris Agreement, which aims to limit the global average temperature increase to 1.5° Celsius above pre-industrial levels.

Specifications for each new locomotive include:

• Low emissions profile (meeting the EU Stage V emission standard)
• 25 per cent reduction in Nitrous Oxide emissions
• 30 per cent reduction in Particulate Matter emissions

DM locomotives have an advanced filtration system that removes 97 per cent of harmful exhaust emissions – a vast improvement over earlier generation diesel locomotives.

Improved traction system design enables:

• fewer locomotives to do the same work
• potential reduction of 20-25 per cent in carbon dioxide emissions through reduced fuel burn and use of onboard technologies
• futureproofing for longer and heavier trains
• Dual cabs to provide operational flexibility
• Equipped with an auto engine start-stop system which can switch off the engine when the locomotive is idling, saving fuel
• Driver energy reduction and advisory system to support the locomotive and drivers to achieve its optimal energy performance

Remote diagnostic system allows KiwiRail to receive:

• Instantaneous fleet geographical location, speed, fuel tank status and battery main switch status
• Summary indication of mileage and energy consumption for each locomotive
• Fault records automatically logged for each locomotive
• Locomotive condition and trending of key parameters

This alone should ensure that they have a service life of at least as long as the DX class, as transport operators are pressured to reduce their reliance on fossil power. Battery electric locomotives (re-chargeable from overhead catenary) are still some way off  as are hydrogen fuel cell locomotives. Read more.

Unloading at Lyttelton Port

Eemslift Nadine berthed in Lyttelton before midnight on 18 October, and unloading commenced at 7.30 am the following day, being completed at 2.15 pm. This was a complex operation because there are no longer railway tracks connecting the wharves with KiwiRail’s yard, so the locos had to be placed onto a heavy-duty low-loader and moved along the wharf to the nearest siding where two DXs were waiting to marshal them for the move to Middleton.

Commissioning and testing at Middleton

The two locomotives are currently undergoing extended testing at both the sub-system level and locomotive level. Static testing includes verification, validation and certification of safety-critical functionalities. Interoperability with other rolling stock will also be verified during this stage.

Main line testing programme

This will commence in January 2025 and will include route clearance runs across multiple networks including MNL, MSL and Midland lines. After dynamic testing is complete, the prototypes will enter regular service around mid-2025. DM locomotives are designed to be used for both passenger and freight duties.

Acknowledgements

Chrissy Farago, KiwiRail for information on design concept, commissioning and testing programme. Brett Congalton, Terra Cat Christchurch for engine specifications and pictures. Darryl Bond, Linesider magazine publisher in Oamaru for cab interior view.

Author

After discharge from 12 years of army service and 14 years in the insurance industry, Chris joined Pacifica Shipping at their Lyttelton engineering workshop where he introduced a job-costing system, provedored four ships. He then managed cargo claims and purchasing. After a brief retirement, he was appointed Member Services Manager for CILT NZ, of which he is a Life Chartered Member. Chris has been involved with railway preservation for 50 years, being a member of the Diesel Traction Group at Ferrymead.  He has a large model railway layout and a particular interest in modern intermodal freight.