Progress Rail has developed gas injection for its engines for Tier III and EPA Tier 4, and SCRs for tug owners that want to continue using diesel
Caterpillar subsidiary Progress Rail, which manufactures EMD (Electro-MOtive Diesel) engines, has introduced dual-fuel engines for a new generation of tugboats that need to operate under the US Environmental Protection Agency’s (EPA’s) and IMO’s stringent emission rules. These engines would mostly use gas as a fuel with diesel just as a pilot.
Dual-fuel engines are based on EMD’s existing diesel-only 710 series E23 engines, They meet EPA’s Tier 4 and IMO’s Marpol Annex VI for IMO Tier III requirements and will reduce fuel consumption for tug owners compared with diesel-only EMD engines, said Progress Rail director of power products Brian Grinter.
EMD diesel and dual-fuel engines are two-stroke and medium-speed for a wide range of applications including power generation on semi-submersible drilling rigs, emergency power on naval ships and main engines on tugs and ferries.
Being two-stroke, they are different from the majority of tugboat engines worldwide, which are four-stroke. Utilising a supercharger or turbocharger, EMD engines can react quickly to the varying loads and operational requirements.
Mr Grinter presented Progress Rail’s engine technology at the British Tugowners Association conference, which Tug Technology & Business attended, in April 2018. He said there are two types of EMD dual-fuel engines available for workboats, which have operational and environmental benefits for owners.
E23 GB uses dynamic gas blending, which substitutes 80% of the diesel with gas and can seamlessly switch between the two without interruption of power output. “This injects gas at low pressure at the bottom of the stroke through the inlet ports,” he said, adding that it would be a good option for upgrade projects. “These retain power output, transient response and reliability of the original diesel engines,” Mr Grinter said.
For newbuilding tug projects, the other engine model, E23 GD, could be used to maximise the use of LNG as it requires minimal diesel use. Mr Grinter said E23 GD has direct injected gas at high pressure and substitutes 95% of the diesel with gas with “the same power and transients as a diesel engine.”
Mr Grinter explained that, if needed, the E23 GD engine could operate up to 30% power on diesel-only. In addition, it has almost no methane slip as the gas injected is completely burnt. Although EMD has not yet sold any dual-fuel engines to tug owners, Mr Grinter expects they will be “a big part of our future sales”.
EMD has also developed engines for tugowners that want to continue with diesel fuel but also want to meet US EPA Tier 4 and IMO Tier III requirements. This involves supplying a selective catalytic reduction (SCR) exhaust gas after-treatment unit with the engine. An SCR injects a liquid-reductant agent, in this case urea, into a diesel engine’s exhaust stream which then passes through a catalyst to remove nitrogen oxides (NOx).
For an EMD E23B engine, the SCR is integrated into the engine with the same footprint as an E23 that does not have a NOx reduction unit. “There is no change in width or length of engine, so it can fit in same space in engineroom,” said Mr Grinter. “We have designed our solution so the SCR can be maintained completely within the engineroom.”
Progress Rail regional support manager for EMD marine products Andy Alexander explained that E23 and E23B engines come in 8-, 12-, 16- and 20-valve versions. They are in a range of 1,250 bkW to 3,730 bkW with running speeds of 750 rpm or 900 rpm and with power development of up to 186 kW/cylinder.
Mr Alexander said these engines have a “two-cycle advantage over four-stroke engine.” The cool, high density charge air delivered to the E23 cylinders across this entire range enables the engine to accelerate from idle of 200 rpm to full power of up to 900 rpm rapidly.
“The transient response from zero to full power driving a fixed pitch propeller is 11 seconds,” Mr Alexander said. In a power generation application, this transient response is just two seconds.
“E23 has a high power-to-weight ratio, allows for easy condition monitoring, lower maintenance and lifecycle advantages over competitive four-stroke engines,” he listed as other advantages.
For example, the turbocharger has 30,000 hours running time before an overhaul is needed. Engine cylinders have the same running hours and there should be no need for mid-life overhauls, said Mr Alexander. There is also no need for oil changes between overhauls.
During planned overhauls the power assembly, head, liner, piston and rod, can all be removed as one unit in less than four hours and the replacement components are light weight.
E23 engines have an inbound overhead camshaft, partially water-cooled exhaust, full liner cooling and closed crankcase ventilation. The fuel oil system has electric-controlled injectors, a mechanical oil filter and centrifuge. Progress Rail developed non-invasive inspection of cylinder components for easy maintenance.
Mr Alexander and Mr Grinter told the conference that these medium-speed and two-stroke engines have many advantages over four-stroke, high-speed engines for tugs. Those same advantages carry over to LNG gas injection versions as well.
• Moran Towing is using E23 engines on 12 of its tugs that operate on the US East Coast. These are on 4,475 kW tugs with twin-screw Z-drive propulsion that, in pairs, handle large container ships using ports of New York, New Jersey and Norfolk in Virginia.
EMD 710 Series E23/E23B ratings
Valves 900 rpm 750 rpm
8 1,491-1,864 1,250
12 2,237 1,560
16 2,983 2,480
20 3,730 3,098
Intermediate ratings are also available
Engines become part of an intelligent propulsion system
Engines should be part of an integrated and intelligent propulsion system to meet IMO Tier III/EPA Tier 4 requirements. They are already connected to propulsion thrusters of various types and sizes and a tug’s automation.
However, analytics and intelligence can be added to these systems, said Caterpillar segment manager John Shock at Riviera Maritime Media’s Sulphur Cap 2020 conference, which was held in Amsterdam, the Netherlands, in April.
“Future designs will require integration of intelligent propulsion systems and technology to meet the demands for efficiency and emissions reduction,” he said at the conference. He expects there will be greater levels of automation and digital analytics “to achieve and maintain [IMO/EPA] compliant operations and to provide compliance documentation.”
Apart from the engines, an integrated propulsion system will include propellers that are optimised using computational fluid dynamics, power management and engine optimisation units and marine asset intelligence, said Mr Shock.
Caterpillar has developed a multi-engine optimiser (MEO) that advises which engines to run and at what load (TTB, Q1 2018). “It uses detailed fuel maps to pick optimum load points for constant speed or variable speeds,” said Mr Shock. MEO runs each engine at this most efficient load point for the power required.
Engine response data facilitates a stable bus in power terms for variable speed operations. It also means medium-speed and high-speed engines can operate on the same bus. Mr Shock said fuel savings could range between 5%-20%, NOx reductions by 5%-50% and overhauls could be extended up to 25%.
Under asset intelligence, engineroom equipment is monitored and analysed. This data is sent to shore for automated and expert analytics that can identify potential issues and develop advisories to vessel managers and masters, Mr Shock explained.