Cat g3520h gensets

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Hart MarineGas engine promises lowest owning and operating costs

Caterpillar's latest gas engine is claimed to offer the lowest cost of ownership and operation for a gas engine in the 2.5 MW power range

Caterpillar has introduced a new generator set G3520H, designed to deliver the lowest owning and operating costs in the market currently.

The new generator is the second one belonging to the H-series product line, and operates on natural gas fuel. The machine is being offered at 2,500kWe power output at 50Hz and 60Hz, stated Caterpillar officials.

The Cat G3520H was specifically designed to improve return on investment (ROI), extended duty combined heat and power and continuous electric power applications. It has an improved electrical efficiency of up to 45.3 per cent and decreased maintenance costs. The generator can be used in hospitals, data centres, manufacturing plants and greenhouses.

Additionally, product developments include cuffed cylinder liners, updated valve stem sealing, and increased valve train lubrication – all of which have minimized the number of maintenance events and reduced oil consumption over previous levels. The new model also features an open combustion chamber design, which allows use of a low-pressure fuel system that facilitates maximum performance on pipeline natural gas.

The major overhaul period of the G3520H is 80,000 hours with an in-frame maintenance interval at 40,000 hours. It has accumulated more than 100,000 hours, and is built on the legacy of the G3500 generator set platform, which has more than 10,000 MWe of power installed.

The machine’s generator set is tailored to specific applications with a wide selection of Cat SR5 generators and attachments, premium controls, exhaust options, remote annunciator modules and battery chargers. The expanded set of features from Caterpillar also includes a complete gas train, package-mounted air cleaners and simplified wiring connections.

Building on a platform


The new engine is the latest mile­ stone in more than three decades of engine evolution. Caterpillar's 3500 series engine platform has been in existence since the early 1980s and has been improved as new technology has become available. The H Series has accumulated more than 100 000 hours and is built on the legacy of the proven 03500 generator set platform, which has over 10 000 MWe of power installed worldwide.

The main focus for technology development over the years has been on improving power density and con­ trolling emissions. Each new series in the platform has therefore looked to improve power density and efficiency compared with its predecessor in these two key areas.

"With the electronics and controls that we can put on these engines also gives us the ability to decrease the cost per kilowatt-hour of the lifecycle cost," said Yohe.

The new engine fills a market gap for Caterpillar, which prior to this did not have a gas product in the 2.5 MW size range. "As for the rest of the H series platform - there is a 16 cylinder engine and a 12-cylinder is being developed - we are really going after the best-in-class life cycle cost," said Yohe.

V20 Design

Development of the H series began in late 2009. Work on this latest V20 en­gine began late 2012/early 2013 and it was released in July 2014 for both the 50 and 60 Hz markets.

"The basic recipe for the platform is what takes time," said Yohe. "And once we have developed the recipe, we have to validate it -not only in the lab but also in the field."

According to Caterpillar, the 16 cylinder version accumulated over 80 000 hours of operation to validate the platform. Yohe added: "To validate the 20-cylinder version, we only had to essentially validate the other four cylinders, so it required  less  hours but you are still in the 15-20 000 hour range for validation of the lower owning and operating cost and service maintenance intervals."

While this is ongoing, technical data work is being undertaken in the lab to verify parameters such as emission levels when using different fuels, altitude and ambient temperature capabilities, etc.

The G3520H has been designed for increased power density. The in­ creased power density of the genera­ tor sets provides a compact size that helps reduce installation costs.

The V20-cylinder engine has a 170 mm bore and stroke of 215 mm. Caterpillar notes that there have been a number of improvements that enable the  increased  electrical  efficiencies and better operational cost. sign that features higher-compression ratio steel pistons, and a high-efficiency turbocharger and electrical genera­tor.

Another major theme was reducing the amount of unburned hydro­ carbons. "There is legislation on un­ burned hydrocarbons in Holland that we meet with this product," notes Yohe.

The G3520H is a spark-ignited with a traditional lean-burn type design. Multiple NOx emissions settings are available, including 500 mg/Nm3 ( l.1 gm/bhp-hr) NOx and 250 mg/ Nm3 (0.55 g/bhp-hr) (50 Hz).

As is common in many  spark-ignited, lean-burn engines, Miller timing is used to control combustion and NOx formation. The Miller cycle differs from the more traditional Otto cycle in that the intke valves close not when the piston reaches bottom dead centre but at typically 10 to 15° before bottom dead centre. This adjustment in the combustion cycle by itself can increase fuel efficiency by about one per cent.

The Miller cycle can be configured as early inlet valve close (EIC) or a late inlet valve close (LIC) version. The EIC camshaft configuration is used on most gaseous-fuelled heavy­ duty  engines. As  the  piston  continues downward with the intake valves closed, the air/fuel mixture expands and thus cools, increasing the detonation margin.

Operational Performance

The engine is capable of fast starts and can operate in island mode. In terms of ramping, it can accept load steps of around 30%.
For applications isolated from a primary electric utility, Caterpillar says the G3520H offers "industry­ leading" load acceptance capability. "These engines can typically be on line in 30 seconds and near full load in that time if ramping load." notes Yohe.

This makes it suitable for supporting wind generation. "We have seen interest in this from the peaking industry - either at the end-use level or at the utility level. In fact one of the first applications for the engine is at a utility in Utah, USA. It is being utilized as a peaking unit that is providing online power to the grid most of the time but is capable of being isolated and running in parallel with other gensets to basically create a local grid," said Yohe.

In the Utah utility application, the engine is installed at about 5400 ft (1646 m) but notably performance is not compromised at higher altitudes and ambient conditions. The engine has updated turbocharger trim options making it capable of running at altitude with similar operating characteristics. "There is a version that is designed to run at high altitudes with minimal power derates and a loss of only a couple tenths of a per cent in efficiency," noted Yohe.


So far, interest in the new engine has been for a mix of peaking and co-generation applications. Caterpillar notes that a number of H series products are also being used in standby applications, where they can also be run in island mode . Caterpillar notes that the unit in Utah can be used in peaking mode or for "storm avoidance", whereby if the grid goes down in a storm, the engine can operate in is­ land mode to provide power.

The engine, however, is primarily targeted at high-hour, base load applications and is therefore designed to be effective in continuous-duty applications. It can be used in industrial and commercial facilities such as hospitals, data centres, manufacturing plants and greenhouses, as well as in distributed generation power plants.

Michael Devine, Gas Product Marketing Manager said: "We do a lot of CHP work with these products in many different markets, it just depends what the applications are. It could be heating and/or cooling - co­ gen/tri-generation. It could even be quadgen where you take the C02 from the unit for greenhouse applications, for ex­ ample, or where the C02 is used for improving plant growth."

The temperature of the heat recovered from the engine for CHP depends on the application. "Basically you would have different temperatures be­ cause of the lean burn design. You can reduce NOx by reducing the temperature in the exhaust so an engine operating at 500 mg/Nm3 would have a higher exhaust temperature than one running at 250 mg/Nm3," explained Devine.

Currently there are a total of five 20-cylinder installations in the field to assess and validate the engines.
Caterpillar currently has "an endurance unit" running at its offices in Lafayette that not only helps offset some of its energy costs but also allows the company to collect running data on the engine. "We have a G3520H at our facility which runs 24/7. We collect data and it reduces our cost of operation by providing us with lower cost electricity," said Devine.

There are also a number of additional units on order. Caterpillar says it is running ahead of schedule in terms of the number of units being ordered and therefore expects to see " a lot more activity in the 6-8 months". 

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Cat G3520H Engine.

The 2.5 MW G3520H was launched in July last year for the 50 and 60 Hz markets.