New Ships to be Powered by Wärtsilä X72 Diesel Engiines
Times of economic austerity in the maritime sector demand of new engines the lowest possible operational costs and best environmental performance, factors that led two Singapore companies to choose Wärtsilä’s recently introduced X72 licensed engines to power four new-build container ships and two bulk carriers now on order in Chinese shipyards. Indeed, Wärtsilä claim that with the X72 engine, compared to similar vessels that have recently been delivered, the bulk carriers’ fuel consumption can be reduced by approximately 5 tons/day, while the container vessels can achieve savings of 4 tons/day.
Wärtsilä had in mind Capesize bulk carriers, and Panamax container vessels just such as these new vessels as ideal applications for the 72-bore engine when they began R&D about two years ago at their Low-Speed Competence Centre in Winterthur, Switzerland.
The Wärtsilä X72 Engine
Image courtesy of Wärtsilä
Basically, this marine diesel engine is a camshaft-less low-speed, direct-reversible, two-stroke engine, fully electronically controlled, designed for running on a wide range of fuels from marine diesel oil (MDO) to heavy fuel oils (HFO) of different qualities.
Requisite for the remarkable fuel economies achievable by this engine is the RT-flex common-rail system, which is employed in special tuning regimes to optimise brake specific fuel consumption (BSFC) at individual engine loads, a concept first applied in Wärtsilä Delta Tuning, now extended to Low-Load Tuning, which provides the lowest possible BSFC in the operating range of 40 to 70% engine load.
The reduced part-load BSFC in Low-Load Tuning is achieved by optimizing the turbocharger match for part-load operation. This is done by increasing the combustion pressure at less than 75% load through an increased scavenge air pressure and a higher air flow (waste gate closed), and by blowing off part of the exhaust gas flow (waste gate open) at engine loads above 85%.The higher scavenge air pressure at part-load results in lower thermal load and better combustion over the entire part-load range.
Low-Load Tuning requires the fitting of an exhaust gas waste gate (a pneumatically operated valve, see schematic below) on the exhaust gas receiver before the turbocharger turbine. Exhaust gas blown off through the waste gate is by-passed to the main exhaust uptake. The waste gate is opened at engine loads above 85% to protect the turbocharger and the engine from overload.
Functional principle of Low-Load Tuning: Schematic courtesy of Wärtsilä
This new X-series engine has numerous features that provide greater operational efficiencies with a reduced environmental impact that include: extended rating fields that offer the optimum propeller speed for different applications; low fuel consumption resulting from the advantageous stroke-to-bore parameters. Last, but by no means least, this engine has an extended interval of five years between overhauls.