TO MEET the latest emissions limits for railcars in Europe, British diesel engine supplier Cummins has announced plans to modify its QSK19-R design with a modular common rail fuel system. The QSK19-R, rated at 650 to 750hp, is being fitted to the 51 three-car TransPennine Express DMUs being built by Siemens for use by Keolis/FirstGroup in northern England (RG 9.05 p568).
The modular common rail fuel system is also to be fitted to the Tier 2 version of the QSK60-L engine, which Cummins is offering to repower HST trainsets operated by GNER on the East Coast Main Line in the UK (RG 11.05 p707). It is also fitted to Tier 3 engines of the same type in the 510 to 700hp range.
With a common rail fuel system, the fuel is held under high pressure at the top of the injector ready for delivery into the cylinders. This avoids the need to have all the pipework pressurised.
Each injector has a pressure-balanced shuttle valve that reacts very quickly to an electrical signal, which allows up to five closely-controlled injection events to take place with every cylinder firing. Using the latest modelling techniques, Cummins has developed a test programme to optimise injector performance. The results of an initial test are used to determine the most likely set of injection parameters to meet the engine’s design objectives. Tests can then be run throughout the engine’s operating range using a recommended trial calibration. If necessary, the operator can retune the modular common rail calibration to give combustion characteristics that suit the after-treatment.
Benefits of a modular common rail fuel system include reduced smoke emission, better idle stability, less idling noise and improved cold start characteristics. Fuel pressure does not depend on the engine speed and load conditions, allowing for flexibility in controlling both the injection rates and timing. This feature differentiates the common rail from conventional injection systems, where injection pressure increases with engine speed. High injection pressures and good spray preparation are possible even at low engine speeds and loads.
CAPTION: Cummins has developed the QSK50T2 engine which meets Tier 2 emissions criteria, and is planning to incorporate the modular common rail fuel system in the QSK50-L version
