converted Mirrlees Blackstone K9 Major diesel engine. The conversion work in a Middle East plant has been carried out by German manufacturer Heinzmann.
With the experience of over 10 years in dual-fuel engine conversions, Heinzmann has recently launched into the conversion of large diesel engines, utilizing the technology of individual cylinder gas admission valves. Hubert Kienzler, program director, Gas Engine Management at Heinzmann in Germany, recently explained the experience his company has accumulated in the field of fuel conversion for diesel engines and the technology behind this type of project. “Heinzmann carried out the first fuel conversion projects with diesel engines in 1995.
At first, these projects involved mainly the supply of components for the conversion, especially controllers. Projects in these 13 years have included stationary gen-sets and compressors, as well as commercial vehicles; and such projects have taken Heinzmann to every corner of the world from Egypt to Brazil, from Uzbekistan to India,” Kienzler said. He added that among the latest projects the company has carried out are three diesel engines in the Middle East. One Mirrlees Blackstone K9 Major that was commissioned in April 2008 and two Mirrlees Blackstone K8 Major that were commissioned in September 2008.
conversion on a Mirrlees Blackstone diesel engine. Below the gas rail is an individual cylinder gas admission valve — the Megasol by Heinzmann.
Kienzler confirmed that for Heinzmann these projects represent the first installation of individual cylinder gas admission valves, which make it possible to balance all cylinders individually. “The system is called Artemis V, and this technology makes the system very attractive for large diesel engines for power generation applications. All these projects refer to gen-sets, and the typical customer for us is a factory with its own power plant, composed of three to six diesel engines in the power range from 1 to 5 MW.”
The availability of natural gas is of course critical, and the Middle East proved to be the perfect cradle for this technology. Kienzler explained that one of the main driving factors for choosing a fuel conversion is that fuel cost is rising. But, he also noted how in this area, there is no regulation for factories to supply electricity to the grid, thus Heinzmann’s customers can use their own electricity production for peak shaving and to reduce power input.
Heinzmann reported an increasing interest in this kind of conversion, with more orders from existing customers, as well as new businesses. The demand comes mainly from regions where electric grid stability is not assured and where natural gas is available without restrictions at a reasonable price. Examples of such areas include Pakistan, Nigeria and Iraq.
The company also pointed out how, depending on engine size, operating hours per day and fuel costs, the investment for the dual-fuel conversion can be paid back in some countries within a few months. The German manufacturer offers a turnkey solution, by supplying the complete conversion kit including all controls, actuators, valves, cable harness, some mounting materials and the gas train.
The customer has to provide for, and install, specific mounting material and the piping while Heinzmann offers its assistance. The dualfuel system is then integrated into the existing compressor or plant management. With its LMG11 or Theseus units, Heinzmann additionally provides the generator control unit for isolated and mains parallel operation. Every project is carried out by Heinzmann, which counts on its own technical support network worldwide.
In several countries the commissioning can be done directly by the local Heinzmann office, and the company calculated an average of one to two weeks after everything is installed for the commissioning of an engine. This depends on the condition of the unit and of the plant.
Kienzler explained that in the conversion from diesel fuel to dual fuel, there are technical limitations arising from the engine itself. “The combustion of gas implies a higher temperature, which causes critical exhaust temperatures. Therefore, for every engine we need to first of all set the limit allowed in terms of temperatures, which we obtain by running the engine with pure diesel and measuring the maximum temperature at full load. This is the threshold we cannot surpass in dualfuel operation.”
Once the combustion temperature limit is determined, the new Artemis V system has the important advantage of allowing individual balance of all cylinders. “It is very important to measure the individual cylinder temperature,” explained Kienzler. “Then, with individual gas admission valves we are able to adjust, singularly, the gas injection per every cylinder, thus balancing all cylinders in terms of exhaust temperature and load.”
He added that the new technology allows the ability to compensate all misbalancing factors related to different behavior in the various components, such as diesel pumps, cylinder and air exchange, gas admission valves and other influences occurring during operation. Kienzler underlined that the control technology of Artemis V also allows it to detect things like cylinder misfiring, gas valve failures and other troubles that can lead to severe temperature changes. Depending on the detected failure, Artemis V will stop the dual-fuel mode or completely shut down the engine.
From his experience in the field, Kienzler reported that in all the installations he has worked with, there was a remarkable misbalancing in the diesel injection, resulting in up to ±50°C variations in the individual cylinders. “By switching over to the dual-fuel mode, after all balancing operations, we were able to set the precise gas amount for every cylinder and limit the variation to only 2°C. The result was a much better engine balancing than before.”
Kienzler also remarked how the diesel pumps play a key role in the final result. “The balancing of the diesel pumps should be optimized as much as possible. Otherwise, if we reduce the amount of diesel in dual-fuel mode to get the maximum conversion ratio, there is a risk that certain cylinders will not fire. In other words: the maximum possible conversion ratio depends also on the diesel pump adjustment.” A rather typical conversion ratio is, for example, 30% diesel fuel and 70% gas but, as Kienzler noted, the exact ratio is determined per every engine during commissioning.
Another interesting component of the dual-fuel conversion that Heinzmann offers as an option is the Ariadne knock controller. This system provides additional engine protection and allows it to safely achieve the set limit in the conversion ratio.
Kienzler illustrated that during the last commissioning, Heinzmann’s technicians found initially that the diesel system adjustment was not working properly. “In one engine, two cylinders were knocking with low gas injection quantities, and Ariadne also detected a cylinder where the knocking was not audibly detectable. A cylinder pressure measurement confirmed the knock measurement result. It was possible then to optimize the timing for the diesel injection to have the best efficiency and the higher gas percentage, while at the same time operating the engine within a safe range.”
The Ariadne control reacts to knocking by reducing the gas percentage with light knocking and by completely switching off the gas mode with heavy knocking. In the wake of the success registered with these fuel conversions, Heinzmann has future plans for additional features. “We are planning to offer to our customers a diesel system exchange, meaning that we can install a small common rail injection system that will provide only a small pilot fuel injection,” said Kienzler. “We will then have an almost pure gas engine with a minimum diesel percentage. The system is currently in development.”
Kienzler concluded by pointing out how the engine condition before the conversion is critical for the commissioning. He said that some of the engines they have worked with were in relatively bad condition, which makes commissioning longer and more difficult. After commissioning, the responsibility for the conversion is referred to Heinzmann. The company has decided to ask customers in the future for an engine recondition, or at least a manufacturer’s service intervention, before the conversion work is carried out.