RELIABLE railway operation in extreme environments poses a host of challenges, not least when it comes to locomotives, which require special design features and technologies to optimise performance in the harshest conditions.

As a diesel-electric locomotive supplier to the Middle East and North Africa regions over many decades, EMD has designed and manufactured locomotives for desert environments including Saudi Arabia, the United Arab Emirates and Mauritania. These locomotives are engineered, optimised and validated to endure harsh climatic conditions and temperatures that can range from -40° to +50°C.

For railways operating in such extreme desert conditions, EMD offers the SD70ACS model locomotive (the second 'S' denoting sand). The SD70ACS is a development of EMD's main heavy-haul freight locomotive, the SD70ACe, which is in widespread use with railways in North America, South America and Australia. The SD70ACS locomotive is equipped with EMD's 3.2MW output 16-710 engine with Tier 3 emissions technology, ac traction, EM2000 microprocessor control system, and an isolated cab. This locomotive is also fitted with ETCS equipment.

In addition to the SD70ACS locomotive, EMD offers the GT46ACS locomotive model for lower axleload applications. The SD70ACS and GT46ACS locomotive models incorporate a number of custom design features and technologies to cope with extreme heat and wind-blown sand.

A key feature is the pulse filtration system, a two-stage active air filtration system which filters fine sand and particulates from the intake air that is delivered to locomotive equipment including the engine, traction alternator, traction motors, electrical locker and compressed air system. Sand removed from the intake air is discarded through a periodic discharge cycle or pulsed air blow down.

Phosphate-Train1Advanced sealing systems are used to minimise sand infiltration. The locomotive cab, carbody, battery box and sub-base compartment doors incorporate special sealing technologies to reduce the ingress of sand. Gear cases are also equipped with a special labyrinth sealing system to prevent the ingress of sand into the traction motor gear case. The SD70ACS and GT46ACS also feature a pressurised bodyshell to further prevent sand from entering the interior of the locomotive.

To guard against sand erosion, both types are equipped with specially-coated radiator cooling fans. Experience showed the high sand concentration in the fast-moving air that passed over the fan blades would reduce the life of the fan as the blades suffered a high level of sand erosion. To combat this, EMD applies a coating to the fan blades to prevent sand erosion, prolonging the life of the fan and ensuring the cooling system operates reliably in the high ambient conditions.

Clearing wind-blown sand from the rails is another key consideration for operation in desert environments, and EMD has recently redesigned its movable sand plough to improve sand clearance capabilities. The locomotive is equipped with two fixed sand ploughs and a third, movable plough that can be lowered at the driver's discretion to remove large sand drifts that can cover the rails.

A specially-designed tropical roof minimises heat transfer into the locomotive cab, and together with the air-conditioning system, provides a safe and comfortable environment for the crew. Filtered make-up air is also supplied to the locomotive cab.

The EMD Engine Control (EMDEC) and EM2000 control systems protect the locomotive from engine overspeed, low water pressure, low oil pressure, hot oil temperature and high crankcase pressure conditions, constantly monitoring onboard temperatures and automatically making adjustments to keep components operating reliably and safely.

A high capacity cooling system is equipped with two, two-speed fans to reduce cooling water temperatures at higher ambient conditions and minimise engine de-rate.

Special blowers are utilised to cool the traction alternators, traction motors and electrical cabinets. The ventilation system is designed and used in conjunction with the EM2000 control system to ensure components operate within permissible limits. The air supplied to these blowers is filtered by the pulse filtration system to prevent sand-filled air from reaching critical components.

A software-based motor management system automatically adjusts tractive effort for prolonged operation during long, heavy hauls at low speeds to protect the traction equipment.

The SD70ACS and GT46ACS are also fitted with a dynamic brake grid system for operation in low humidity environments.