Rolls-Royce Power Systems explains why it built LNG-powered engines, instead of using a dual-fuel unit
There are a growing number of dual-fuel engines that use both diesel and natural gas and a growing requirement to develop main propulsion engines that purely burn gas for applications including OSVs.
Rolls-Royce Power Systems has developed gas-fuelled engines and generator sets for offshore support and oceangoing towage vessels. Its main product for these vessels is a new 16-cylinder pure gas engine, based on MTU’s proven 16V 4000 M63 diesel engine, with a power output of 1,492 kW.
Rolls-Royce Power Systems says it has also produced an eight-cylinder version with an output of 746 kW. These units would be suited to special purpose vessels, smaller OSVs, tugboats, ferries and push boats.
“The dynamic acceleration behaviour and the possibility to install direct mechanical propulsion systems with fixed propellers are suitable for various commercial vessels,” says Rolls-Royce Power Systems commercial marine applications engineer Cyrill Halbauer.
Both engines exceed compliance with IMO Tier III and US Environmental Protection Agency’s Tier 4 emissions requirements “with no sulphur oxide emissions and very low nitrogen oxide and particulate matter, which are below the verification limit,” says Mr Halbauer.
“Dual-fuel engines tend to have a higher impact on the weight of the propulsion system”
Early deliveries of the eight- and 16-cylinder engines have been for commercial vessels and ferries. Mr Halbauer says pure gas engines were developed, instead of a dual-fuel version, as these would have had higher complexity, “since two different types of fuel need to be taken into account”.
He continued: “Dual-fuel engines tend to be heavier and therefore have a higher impact on the weight of the propulsion system.”
MTU is also supplying more of its diesel engines in combination with electrical components for offshore vessels, says Mr Halbauer.
“In recent years, there has been interest in variable-speed units as a driver of commercial vessels, such as OSVs,” he says. “Variable-speed technology allows the speed of an engine to be regulated and adjusted according to the electrical load that is connected, which makes it more economical to run.”
Compared to traditional, constant-speed units, variable units can offer several advantages, such as up to 15% reduction in fuel consumption, up to 20% increase in time between overhauls, lower noise emissions, engine-sensitive operations and increased power density.
Rolls-Royce Power Systems will be offering complete hybrid propulsion systems for vessels. These will consist of MTU combustion engines, electric drive modules, transmission systems, batteries, monitoring and control systems.
Mr Halbauer says these systems will be offered in a variety of power ranges to suit individual vessel operator requirements. Systems incorporating MTU Series 2000 engines, combined with variable electrical power, will be launched first. These will cover a power range of 1,000- 2,200 kW per power train.
“Step-by-step, MTU will then extend its portfolio with the addition of hybrid systems based on the power delivered by MTU Series 4000 engines and variable electrical power, and will cover a power range of 1,000-4,000 kW per powertrain,” says Mr Halbauer.
MTU will focus on power take-in (PTI) solutions and gradually introduce inline solutions. With its PTI product, the gearbox is connected to the diesel engine via a clutch. “To this PTI gearbox, an electric motor is attached which can be coupled or decoupled as needed,” Mr Halbauer explains.
The MTU inline solution consists of an intermediate shaft gearbox that is flanged between the diesel engine and the transmission gear unit. At this intermediate shaft gearbox, up to four electric motors (depending on customer and performance requirements) would directly be attached.