Fuel flexibility of future combustion engine power plants
Päivi Aakko-Saksa, Sami Nyyssönen, Tuula Kajolinna, Raimo Turunen (VTT Technical Research Centre of Finland Ltd), Juha-Pekka Sundell (Wärtsilä Energy Solutions), Lauri Pirvola, Tuomas Niskanen (Gasum Oy), Pekka Hjon (AGCO Power), Seppo Niemi (University of Vaasa), Teemu Sarjovaara (Aalto University)
The most important challenges that the world faces today relate to climate change and energy security. There are proposals to reduce the greenhouse gas (GHG) emissions of developed countries by at least 80% by 2050 compared to 1990 . Furthermore, regulations for other emissions are tightening.
New alternative and renewable fuels for internal combustion engines can contribute in meeting future targets. A spectrum of fuel options is available, including various liquid and gaseous fuels.
The Future Combustion Engine Power Plant (FCEP) research program in Finland belongs to the Cluster of Energy and Environment (CLEEN Ltd., currently CLIC Innovation), which aims at maintaining and developing an open innovation platform for market-driven joint research between industry and academia. Work Package 4 (WP4) of FCEP focused on fuel flexibility in combustion engines. In this work, fossil, bio and other alternative fuels were considered for engine power plants, ships and high-speed engines at least for the next 40 years. The quality of fuels was considered together with the needs of engine and emission control technologies. This article discusses the main results of the fuel flexibility-related issues of FCEP WP4.
LNG and Biogas
The shipping sector will face major challenges with new emission regulations. Emission Control Area (ECA) requirements shifting from a fuel oil-based to an LNG-based shipping industry will have the potential to reduce carbon dioxide (CO2), nitrogen oxides (NOx) and sulphur oxides (SOx) emissions. The main challenge is an insufficient LNG fuel infrastructure. The work at hand investigated LNG logistics and bunkering solutions for the Finnish market . The various steps in the LNG logistics chain and a number of attributes for each logistical component were analysed: description, technology maturity and experience, references, economic aspects, space and site requirements, size, scalability, flexibility, limitations, feasibility and risks. The assessment of a possible LNG distribution system for the Finnish marine LNG market concludes that the development will most probably be phased but with a focus on the main RoPax (vessels for wheeled cargo and passengers) and RoRo (roll-on/roll-off vessels for wheeled cargo) hubs in the western and southern coast of Finland. Potential hazards in the LNG logistics chain for maritime applications were identified and ranked in terms of consequence and probability, and mitigating measures for the various hazards were mapped out.
A comprehensive supply chain is the main challenge for LNG, which was studied by Riaz . Natural gas harmonisation, interoperability and interchangeability are the additional new focus areas for the Finnish natural gas market. New markets demand an LNG with quality compatible to existing pipeline grid and clientele specifications. Production, liquefaction, storage, transportation and regasification are among the main components of the LNG value chain. A preliminary simulation was conducted for enhancing the LNG methane number through the LPG extraction process by means of Aspen HYSYS software.
Three interchangeability parameters of natural gas were taken into account: methane number, Wobbe index and lower heating value. On comparing the available and the required LNG quality, limited LNG sources for the Finnish natural gas market were found without at least some processing before injecting into the Finnish natural gas grid. The strict criterion is based on the methane number requirement of 87 by the existing Finnish grid operated by Gasum. A variety of technologies to improve and manage LNG quality are available at LNG receiving/import terminals. A basic simulation process for LNG quality management compares three preliminary methods to adjust the quality of imported LNG to reduce heating value :
Case I. Extraction of LPG
Case II. Injection of nitrogen (nitrogen ballasting)
Case III. Injection of CO2 (CO2 ballasting)
As portrayed in Figure 1, Case II is the most energy intensive of these processes. Biogas can reduce life cycle CO2 emissions, but the quality of biogas is not sufficient for internal combustion engines without upgrading, i.e. the removal of CO2 from raw biogas to increase its methane content. Water scrubbing, PSA and chemical absorption are popular technologies for upgrading of biogas. Costs of upgrading are dependent on the technology and size of the plant.
No upgrading technology is suitable for all applications: case-by-case choices are needed to provide a sufficient quality of biogas for the natural gas grid or other applications.
In general, all upgrading technologies are under constant development and this is expected to have a positive impact on cost levels.
A special issue regarding biogas from wastewater and landfills are siloxanes originating from hygiene, health care and industrial products. Siloxanes are harmful for engines even at low concentrations. The test bench for siloxane removal technologies was built up at VTT. Three market leading siloxane removal adsorbents were tested: activated carbon, molecular sieve and silica gel-based media. Three siloxane removal systems performed well in the tests, but differences in efficiencies and cleanliness of purified biogas were observed. In the evaluation of the siloxane monitoring systems, 12 were found capable to measure low siloxane concentrations. The detection limits and specificity varies substantially, and portable monitoring systems were not easily available.
Modelling Fuel Performance in an Engine
An attempt was made to model the performance and emissions of an engine using a particular fuel based on its chemical and physical properties. Two simulation softwares, GT-Power and Diesel-RK, were used to build models to predict the ignition and combustion of the fuels. It was demonstrated that the characteristic changes in engine operation by changing the fuel could be simulated with the predictive tool. However, the simulation model required calibration for each case, thus making engine testing a necessity .
Unconventional and Difficult Fuels for Medium-Speed Engines
Some difficult fuels cannot be used in engines without fuel pre-treatment. In this work, new pre-treatment methods were developed. Remarkable success was achieved with the theory behind the agglomerates, also known as phosphate lipids (Figure 2), which is a challenge for fuel filters. Fibres were found from crude palm oil (CPO), which will affect filters in a negative way. For the fibres, mechanical manipulation tests were conducted. Different kinds of washing methods for filters were also developed .
Water degumming is a process that decreases the content of inorganic particles, fibres and gum-forming oil components in crude vegetable oil. The main purpose was to produce oil that doesn’t form deposits during transportation and storage. Methods were developed as laboratory size tests and continued as engine size tests. A totally new kind of filter unit for liquid biofuel (LBF) was developed.
The deterioration of oils and fats is a sum of different factors which all involve various chemical, physical and biological mechanisms. A study was performed on the stabilisation of plant oils and animal fats in comparison with ester-type biodiesels.
LBF fuels with poor cold properties were successfully used in winter conditions in a containerized 9L20 (1.6 MW) power plant. All fuels tested were suitable for use even in cold conditions; however, chicken oil showed some problems.
With VTT’s Wärtsilä Vasa 4R32 engine, almost 20 combinations of fuels were studied . Using fractions currently nominated as hazardous waste would allow recycling of fuels. A medium-speed engine was used in two modes: LN configuration uses standard mechanical injection system and the GD injection system is a dual-fuel arrangement. For dual-fuel tests, the standard Wärtsilä GD-injection system was modified to accept liquid and liquefied fuels .
Single-fuel tests included light fuel oil (LFO), animal fat, shale oil, tyre pyrolysis oil and hexane fuels. LFO was used as a reference fuel in both LN and GD engine modes . Actual test fuels were conducted into cylinder trough LN or GD (pilot side) standard injectors, except for two cases in which LN engine mode with modified W20 engine injector nozzle tips were used (reduced injector fuel hole diameter).
Engine development may increase possibilities to utilize new alternative fuels for mobile machinery. For conventional diesel engine of non-road machinery, these alternatives cover basically an ester-type FAME biodiesel and paraffinic HVO-type renewable fuel.
The literature study showed that FAME fuels have been problematic as regards storage stability . In addition, phosphorus present in FAME is harmful for catalysts. The chemical composition of FAME varies quite considerably depending on the production site and raw material leading to regional variations in fuel composition. Exhaust after-treatment systems are introduced today to non-road mobile machinery, such as exhaust gas recirculation (EGR) plus diesel particulate filter (DPF) or diesel oxidation catalyst (DOC) plus SCR (selective catalytic reduction). AGCO Power selected SCR technology, because it gives clear benefits in fuel economy, base engine durability and cooling capacity. If an engine manufacturer gave an approval to use FAME fuel, it should be applicable in all regions where quality-controlled FAME is available.
The 500-hour B20 test was conducted with a modern off-road diesel engine driven with a fuel blend of ordinary diesel fuel oil (DFO) and soybean methyl ester (SME) for a period of 500 hours . The B20 blend was doped to contain sodium (Na) and potassium (K) 10 parts per million (ppm), calcium (Ca) and magnesium (Mg) 10 ppm and phosphorus (P) 4 ppm before preparing the blend. The risk of damage can be considered noticeable even though FAME quality would be controlled according to proper standards. The conclusion was that 20% FAME blend cannot be recommended for the state-of-the art heavy-duty engines without revising the alkali and earth alkaline metals limits of EN14214 diesel fuel standard.
A turbocharged, intercooled high-speed non-road diesel engine was driven with HVO, biodiesel from fish wastes (FISH ME), and animal fat-based methyl ester (AFME). [8, 9] In addition, four different injector tips were investigated, running the engine on DFO. Regarding exhaust smoke at part loads, some advantages were achieved with the eight-hole low-flow (LF) injection nozzles.
One pathway to use alternative fuels for non-road machinery is the development of a diesel-ignited dual fuel engines. Here, focus was on a dual fuel engine using ethanol as the main fuel and diesel fuel for ignition. Because ethanol is relatively cheap and plentiful on sugar cane farms and basic diesel-powered tractors are used, the objective was to study if a standard diesel engine could be modified to run with ethanol as primary fuel, ignited with diesel fuel.
Two dual-fuel test engines were built up, the second one by using a 6 cylinder 7.4 litre engine as basis, having a common rail system and 2-valve cylinder heads. The main modifications included intake manifold with individual ports for ethanol injectors and lower waste gate opening setting . Separate but interconnected ECUs were used for diesel and ethanol control. The performance targets were met and the engine can be switched from diesel to dual fuel at any time without any noticeable change in engine performance or driveability. The diesel substitution rate was 20–70% depending on speed and load. In addition, performance in 100% diesel operation was not compromised.
Exhaust emission measurements showed that the premixed ethanol increases hydrocarbon (HC) and carbon monoxide (CO) comparable to spark ignition (SI) engine level, whereas the dual-fuel combustion reduces NOx compared to 100% diesel fuel. Particulate matter (PM) emissions are typically lower for ethanol than for diesel fuel. It was possible to reach Tier 3 level by making some modifications in the charging system and diesel parameters and adding an oxidation catalyst.
Summary and Conclusions
Fuel flexible engines represent a pathway to cope in the increasingly complex fuel market.
LNG was found to be the potential fuel to respond to upcoming emission requirements, but insufficient infrastructure presents a weak spot for large-scale use. Various steps to improve LNG logistics in Finland were explored. A suitable LNG distribution network was found to probably focus on the main RoPax and RoRo hubs along the western and southern coasts of Finland. The challenges associated with the LNG supply chain relate to harmonisation, interoperability and interchangeability.
Production, liquefaction, storage, transportation and regasification are among the main components of the LNG value chain. LNG sources suitable for import to Finland were identified based on specifications set by national natural gas applications. Methane number was the deciding factor for appropriate LNG variety available worldwide. Technologies available for LNG quality improvement and management were also evaluated.
The quality of biogas as such is not sufficient for internal combustion engines; CO2 and different impurities need to be removed. Water scrubbing, PSA and chemical absorption are popular technologies, with costs of upgrading dependent on the technology and size of the plant. Siloxanes present in biogas from wastewater and landfills are harmful for engines even at low concentrations. Three siloxane removal systems performed well in the tests, but differences in efficiencies and cleanliness of purified biogas were observed. In the evaluation of the siloxane monitoring systems, 12 were found capable to measure low siloxane concentrations. The detection limits and specificity varies substantially, and portable monitoring systems were not easily available.
For difficult fuels, pre-treatment methods were developed and remarkable success was experienced with new washing methods and fuel filters. For plant oils, animal fats and esters, the efficiency of antioxidants was shown to be fuel-dependent. Use of several liquid biofuels with poor cold properties performed well in winter conditions in a containerised 1.6 MW power plant. With medium-speed Wärtsilä Vasa 4R32 engine, almost 20 combinations of fuels were studied in standard LN configuration and with the modified GD injection system. Improvements in injection system performance, controllability and efficiency were made.
For conventional diesel engines of non-road machinery, paraffinic HVO-type renewable fuel shows generally good performance, whereas ester-type FAME biodiesel is problematic. This work showed that a 20% FAME blend cannot be recommended for the state-of-the art heavy-duty engines equipped with emission control device without revising the metal limits of EN14214. Tests with fish oil and animal fat esters were conducted with a turbocharged, intercooled common-rail high-speed engine. NOx emissions were higher for esters than for diesel fuel at high loads, whereas the lowest high-load NOx was measured for paraffinic HVO. The lowest smoke readings were recorded for esters, but HVO also resulted in lower smoke than conventional diesel fuel oil.
For non-road machinery, a diesel-ignited dual-fuel ethanol engine was developed. Depending on speed and load, 20% to 70% of diesel consumption can be replaced with ethanol without compromising 100% diesel operation. It was possible to reach Tier 3 emission level by making some modifications and by adding an oxidation catalyst.
A wide range of issues related to fuel flexibility of medium-speed engines and machinery was studied. These steps pave the way towards increased fuel flexibility, and consequently, better energy efficiency. Lower CO2 emissions and environmental impact of the current combustion engines were also sought.
The FCEP program supported close cooperation of industrial and research partners. This kind of cooperation and further development is still needed.
This article was derived from Paper #2016|070 presented at the CIMAC Congress in Helsinki, Finland, June 6-10, 2016. Published with permission from CIMAC.
 IEA, “Energy Technology Perspectives”, 2010. ©OECD/IEA 2010.
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