Upgrade for popular four-stroke engine
Wärtsilä explains how over the last two years it has been carrying out a test programme of improvements to its 32cm-bore four-stroke engine, to provide claimed best-in-class power density and fuel economy across a broad operating range, with rated power up by 15%.
The upgraded Wärtsilä 32 now produces 580kW/cylinder at 750rpm, and is available in six-eight- and nine-cylinder in-line, and 12- and 16-cylinder V versions; representing a total rated engine output range of 3.5MW to 9.3MW. It can operate on HFO, light distillate fuel and liquid bio fuel with a broad range of fuel viscosities, from 2.0 cSt up to 730 cSt HFO (at 50 °C/122 °F). The engine will operate efficiently and economically on low sulphur fuel oils (<0.1% S), making it suitable for operation in ECAs. It fulfils the IMO Tier II regulations as set out in Annex VI of MARPOL 73/7. It can also be equipped with SCR, such as the Wärtsilä nitrogen oxide reducer (NOR), to provide Tier III compliance.
The cylinder output of the Wärtsilä 32 engine has been increased six times since 1980. In 1980, the first 32 engine had 308kW/cylinder. Over some 30 years, 4,000 of the engines have been delivered to the marine market alone. It has a proven track record in a range of vessel applications, including as main propulsion, both direct mechanical drive as well as diesel electric, and as an auxiliary engine. It can be optimised for either constant speed or along a combinatory curve.
In the merchant fleet, typical applications include use as the main engine on different types of tankers and container vessels. In the offshore sector, the Wärtsilä 32 is claimed to be the most popular medium-speed engine for offshore service vessels and drilling vessels. The Wärtsilä 32 has enjoyed similar success in the cruise and ferry sector. As an auxiliary engine, the Wärtsilä 32 is widely utilised in all vessel categories where high electrical load is needed.
The upgraded Wärtsilä 32 is based on the same proven technology and design principles as the current Wärtsilä 32 engines. It is a turbocharged four-stroke diesel engine with direct fuel injection and charge air cooling. The cylinder bore is 320 mm and the stroke is 400 mm.Because the basic technology was already in place, the project proceeded very rapidly. Development began after official approval in October 2009, and the first 6-cylinder proto engine was started successfully at the Vaasa factory’s test run cell in September 2010.
The Wärtsilä 32 pilot sales release took place in November 2010 and the first customer order was received in April 2011. The Type- and Engine International Air Pollution Prevention (EIAPP) tests with classification societies were completed by the end of September 2011. Assembly of the first pilot engines began during August and the testing was completed at the Vaasa factory by the end of October 2011. The development project itself was closed at the end of January 2012.
It was clear from the start that the most suitable way to improve the power density and product cost ratios was to increase the firing pressure. For this, it was necessary to optimise the combustion and employ high efficiency turbocharging. The firing pressure has been increased from 21MPa to 23MPa.
However, while increasing the firing pressure, it was also necessary to ensure that reliability was maintained and that the prospective commonality with gas engines could be ensured. This meant the redesign of several components. Attention was paid to environmental aspects such as noise and exhaust gas.
The engine block is based on the established Wärtsilä 32, with the cylinder head bolt thread size increased from M56 to M60. The bore for the cylinder liner is increased to enable the future use of a gas engine cylinder liner with 340mm cylinder bore.
The camshaft bearing diameter has been increased from 190mm to 230mm and the centreline is moved 20mm downwards to give more space for better serviceability. The cam profiles are new and performance has been optimised.
The cylinder head casting is common to that of the gas engines. The design has been strengthened in many ways, for example by improving the flame plate. Attention has also been paid to easing serviceability. The crankshaft has a new strengthened design with thicker crank webs. The engine covers feature improved noise reduction and are common with those for gas engines. The connecting rod design is the same three-piece design, known as the ‘marine-design’, as the older Wärtsilä 32, but a harder material has is now used. The three-piece design reduces the height required for piston overhaul, a task which can be undertaken without touching the big-end bearing, while the big-end bearing itself can be inspected without removing the piston.
The conventional fuel injection system has been upgraded with increased injection pressure and volume. The Wärtsilä 32 engine is designed for continuous operation on HFO as well as LFO. A pre-heated engine can be started directly on HFO provided that the external fuel system has the correct temperature and pressure.
Due to the increased charge air pressure ratio and efficiency, a new turbocharger version has been introduced. Both turbocharger types are connected to the engine lubricating oil system. The re-designed charge air cooling system provides better engine performance and commonality with gas engines. The exhaust system remains the same, with the exhaust waste gate and by-pass system identical to that used on gas engines. For offshore sector use, a charge air blocking device will be available. The various changes to the charge air system have led to a new design for the insulation box, heat- and noise coverings.
The starting air system has had several improvements, including a new main starting valve, resulting in a faster overall functional speed of the system. Again, attention has been paid to ease of assembly and thus serviceability, and commonality with gas engines.
The UNIC C2 engine control system is used on the upgraded engine without major changes, but some previously optional features are now standard, including engine slow turning and the temperature monitoring systems for cylinder liners and big end bearings.
The UNIC C2 is an embedded engine management system, designed for the marine environment with special attention to temperature and vibration endurance. This allows the system to be directly mounted on the engine, resulting in a compact design without the need for components to be mounted in external cabinets or panels. It also allows the engine to be delivered fully tested at the factory, meaning that the engine or generating set can be operational with a minimum of commissioning and installation work.
The modular and standardised interface enables integration with off-engine automation systems, for example, conversion of diesel engines to dual-fuel or common rail engines can be achieved with a minimum of modifications. The critical parts of the UNIC system are either redundant or highly fault-tolerant to guarantee safety and availability. In particular, parts like the communication and power supply are fully redundant to allow single failures without interruptions to the engine’s operation.
Testing of the Wärtsilä 32 started in September 2010, and the first engine was moved to the engine laboratory in October. The main focus of the early tests was on optimising engine performance for constant speed applications. Fuel consumption, emissions and thermal load were according to expectations. A load acceptance optimisation test was also performed in order to reach the three-step loading target.
Testing continued until the beginning of 2011 with product validation tests, such as vibration, stress, temperature and pressure pulse measurements, to provide component data for extended maintenance-free operation,- and thus maximum revenue-earning capability. The engine then began endurance testing, with around 3,750h operation expected to be completed in the laboratory before the end of 2012.
The main drivers for the upgrade design were high power density, control of product costs, and commonality with gas engines. In simple terms, this means more power with fewer cylinders to overhaul. The engine is designed for long periods of maintenance-free operation and has overhaul intervals of up to 24,000 hours with low consumption of spares. This, and the maintenance-friendly design, serves to reduce downtime, promote scheduling, and cut operating costs. Together with dynamic maintenance planning and service agreements, the overhaul interval time for the Wärtsilä 32 can be extended further.
The Wärtsilä 32 has been designed to operate reliably on a range of fuels, including HFO, MDO and liquid bio fuels, and even with the poorest quality of heavy fuel. In all cases it has shown proven reliability, high power density, and low fuel consumption over a wide load range. Additionally, the high degree of commonality with gas engines makes future conversions to, for example, dual-fuel, very easy.
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