Hitachi Zosen was awarded a contract in March 2007 by Wärtsilä Corporation to build four six-cylinder Wärtsilä RT-flex50-B engines for ships to be built in China
. The first of the ships will be delivered in the second quarter 2009. The engines each have a maximum continuous power of 9960 kW (13,560 bhp) at 124 rpm.
Wärtsilä RT-flex marine low-speed engines incorporate the latest electronically-controlled common-rail technology
for fuel injection and valve actuation. The new technology provides great flexibility in engine setting, bringing benefits in lower fuel consumption, lower minimum running speeds, smokeless operation at all running speeds, and better control of other exhaust emissions.
RT-flex engines are available in eight cylinder sizes covering a power range from 5800 to 80,080 kW. The Wärtsilä RT-flex50-B is the smallest of these, providing prime movers of 5800 to 13,280 kW ideally suited to the propulsion of bulk carriers in the Handymax to Panamax size range, product tankers and 900-1500 TEU feeder container vessels. It is designed to meet the market needs for outstanding reliability, high efficiency, compactness, optimised manufacturing, and environmental requirements. As with all new marine engines nowadays, it is fully compliant with the NOx emission regulation of Annexe VI of the MARPOL 1973/78 convention.
The first RT-flex50 engine entered service in January 2006. The engine type has been very successful in the market with some 85 engines already sold.