Future Combustion Technology for Synthetic and Renewable Fuels in Compression Ignition Engines (REFUEL) - Final report

This domestic project, Future Combustion Technology for Synthetic and Renewable Fuels in Compression Ignition Engines (ReFuel), was part of a Collaborative Task "Future Combustion Technology for Synthetic and Renewable Fuels in Transport" of International Energy Agency (IEA) Combustion Agreement. This international Collaborative Task is coordinated by Finland. The three-year (2009-2011) project was a joint research project with Aalto University (Aalto), Tampere University of Technology (TUT), Technical Research Centre of Finland (VTT) and Åbo Akademi University (ÅAU). The project was funded by TEKES, Wärtsilä Oyj, Neste Oil Oyj, Agco Sisu Power, Aker Arctic Technology Oy and the research partners listed above. Modern renewable diesel fuels have excellent physical and chemical properties, in comparison to traditional crude oil based fuels. Purely paraffinic fuels do not contain aromatic compounds and they are totally sulphur free. Hydrotreated Vegetable Oil (HVO) was studied as an example of paraffinic high cetane number (CN) diesel fuels. HVO has no storage and low temperature problems like the fatty acid methyl esters (FAMEs) have. The combustion properties are better than those of crude oil based fuels and FAME, because they have very high cetane numbers and contain no polyaromatic hydrocarbons (PAH). With low HVO density, viscosity and distillation temperatures, these advantageous properties allow far more advanced combustion strategies, such as very high exhaust gas recirculation (EGR) rates or extreme Miller timings, than has been possible with current fossil fuels. The implementation of these advanced combustion technologies, together with the novel renewable diesel fuel, brought significant nitrogen oxides (NOx), particulate matter (PM) emission reductions with no efficiency losses. The objective of ReFuel project was to develop new extremely low emission combustion technologies for new renewable fuels in compression ignition engines. The target was to decrease emissions at least by 70%. The scope was to utilize the physical and chemical properties of the renewable fuels that differ from properties of the traditional crude oil based fuels and to develop optimum combustion technologies for them. The project focused firstly, on paraffinic high cetane number fuels i.e. hydrotreated vegetable oil fuel as a typical representative of this kind of fuel and secondly, on fuels with high content of oxygenates. This was implemented by blending oxygenate to HVO fuel.

Effect of negative valve overlap in a heavy-duty methanol-diesel dual-fuel engine : A pathway to improve efficiency

Funding Information: The authors would like to acknowledge the receipt of the following financial support for this research work and authorship. This work was financially supported by Academy of Finland (grant no. 13297248) Fortum-Neste Foundation (grant no. 2020050 and 20210032 ), and Merenkulun säätiö (grant no. 20210073). Publisher Copyright: © 2022 The Author(s)Methanol (MeOH) is a promising low-carbon liquid fuel to provide global energy security with a potential to achieve net-zero greenhouse gas emissions in transport sector. However, its utilization in diesel engines at high MeOH substitution ratios (MSR) suffers from misfire or high pressure rise rates owing to its distinct physio-chemical properties. This issue is addressed in the present study by adopting negative-valve overlap (NVO) and hot residual gases from the previous cycle. Experiments are performed in a single-cylinder heavy-duty CI engine for a constant MSR (90% energy based) and an engine speed of 1500 rpm. The aim of the study is to investigate the effects of 1) NVO period, 2) charge-air temperature (Tair), 3) MeOH lambda (λMeOH) on the MeOH-diesel dual-fuel (DF) combustion in NVO mode, and 4) to demonstrate the implications of NVO in yielding high net-indicated efficiency (ηind) together with low pollutant emissions at a wide range of engine operating loads (40–90%). The results show that the hot residual gases from the previous cycle enhance the reactivity of the fresh MeOH-air mixture by inducing slow oxidation processes before TDCf. The slow pre-flame oxidation processes are disruptive or oscillatory in nature, wherein NVO period, Tair and λMeOH can be used to control these processes and their induced reactivity enhancing capability. It is noticed that the pre-flame oxidation processes and the main combustion have a direct correlation between them. Based on the control strategy, the MeOH-diesel combustion in the NVO mode produced on average ηind of approx. 53% accompanied with very low NOx emission of 1.1 g/kWh at a wide range of engine operating loads (40–90%). Additionally, on average the combustion phasing (CA50) is maintained at ∼ 2 oCA aTDC, while the combustion stability remains high (COVIMEP ∼ 3.5%).Peer reviewe

Effect of pilot fuel properties on lean dual-fuel combustion and emission characteristics in a heavy-duty engine

| openaire: EC/H2020/634135/EU//HERCULES-2In a dual-fuel (DF) combustion process, the ignition of the main fuel plays a crucial role on engine performance and emissions. In the present work, a pilot fuel is used to ignite a gaseous methane-air mixture. Three diesel-like pilot fuels are used comparing especially the cetane number (CN) and the aromatic content (AC). The experiments are conducted in a single-cylinder heavy-duty research engine keeping the total-fuel energy constant. Lean conditions are applied for the port-fuel injected methane-air mixture (∅CH4 = 0.52). The methane provides 97% of the total energy while 3% of the energy comes from a pilot fuel. The experiments are performed for two pilot-fuel injection pressures and two engine speeds. The results of the present work suggest that DF combustion consists of three overlapping combustion stages: (I) ignition of the pilot fuel, (II) burning of the main fuel in the vicinity of the pilot fuel, and (III) combustion of the remaining main fuel. It was observed that cetane number directly affects the peak heat-release rate (HRRpeak) during Stage I, whereas aromatic content influences HRRpeak during Stages II and III. A fuel with high cetane number and aromatic content provides high DF combustion efficiency, low methane slip, THC and CO emissions at the expense of high NOx emissions. An increase in the aromatic content is responsible for the increased NOx emissions. Based on the average performance trends of the pilot fuels, they can be rated as [high CN, high AC] > [Low CN, high AC] > [High CN, AC free].Peer reviewe

Optical investigation of spray characteristics for light fuel oil, kerosene, hexane, methanol and propane

| openaire: EC/H2020/634135/EU//HERCULES-2The present study investigated liquid fuel spray penetration and opening angles for EN 590 light fuel oil (LFO), kerosene, hexane, methanol, and propane. Moreover, droplet sizes were studied for methanol and light fuel oil sprays from a single location at the edge of the sprays. The fuels were injected from a marine-size common rail diesel injector into a constant volume spray chamber with nitrogen atmosphere, and the results were based on shadow image analysis. The results indicated that propane sprays would penetrate slower and less than the sprays of the other fuels, but the differences seemed to decrease when increasing chamber density. With the exception of the lowest tested chamber density of 1.2 kg/m3, propane formed significantly narrower liquid sprays than the other fuels. Apart from propane, the fuels had mostly similar responses to increased chamber densities. Variations between repetitions were large in comparison to the differences between the liquid fuels. Concerning droplet size measurements, the results suggested that methanol sprays would contain slightly smaller droplets than LFO sprays in the tested conditions. This finding agrees with an earlier study, albeit the found differences were considerably smaller.Peer reviewe

Modelling the end-use performance of alternative fuel properties in flex-fuel vehicles

Funding Information: This work was a part of the ADVANCEFUEL project, European Union's Horizon 2020 project under grant agreement N.◦764799. The authors would like to also acknowledge support from Neste and Fortum Foundation, the branch group Combustion Engines Finland (Teknologiateollisuus), Henry Ford Foundation and the Finnish Foundation for Technology Promotion (Tekniikan Edistämissäätiö). Funding Information: This work was a part of the ADVANCEFUEL project, European Union’s Horizon 2020 project under grant agreement N. ◦ 764799. The authors would like to also acknowledge support from Neste and Fortum Foundation, the branch group Combustion Engines Finland (Teknologiateollisuus), Henry Ford Foundation and the Finnish Foundation for Technology Promotion (Tekniikan Edistämissäätiö). Publisher Copyright: © 2022 The AuthorsRenewable fuels and fuel-optimized engines play a key role in the time- and cost-effective decarbonization of current mobility. The present work introduces a state-of-the-art mathematical model that allows for the first time an accurate estimation of fuel consumption in flex-fuel vehicle engines by considering the impact of the most significant fuel properties exclusively. These engines are optimized to a higher concentration of non-drop-in fuels such as E85. Based on the literature data, a matrix was built with fuel properties as multiple independent variables and fuel consumption as a response variable. A multilinear regression with quantitative analysis was applied to develop a fuel consumption model for FFVs. The most significant fuel properties turned out to be octane sensitivity, vapor pressure, lower heating value, and density. All properties in the final model have a unique and important impact on fuel consumption, secured by extremely low p-values (P ≪ 1 %). The model reached very high accuracy represented by R-Square of 0.994, which turned into 1.41 % of the average absolute error in internal validation and only 1.9 % in external validation. The present study shows that in all alternative fuel cases, flex-fuel vehicles performed with better fuel economy than standard spark-ignition light-duty vehicles. Moreover, high concentration alcohol blends reduce energy consumption as well as tank-to-wheel CO2 emissions despite their higher fuel consumption. The developed model can be applied to fuel consumption estimations in FFVs from single chemical compounds to commercial fuel products including new fuel blends.Peer reviewe

Cycle-to-cycle variations of dual-fuel combustion in an optically accessible engine

Cyclic variations constitute an inherent consequence of the flow, thermal and concentration field variations between cycles. They are understood to lead to lower efficiency and higher emissions. The current investigation aims to evaluate the cycle-to-cycle variations (CCVs) based on 2D visualization and cylinder pressure in an optically accessible heavy-duty engine fueled with methane (main fuel) and diesel (pilot fuel). A high-speed color camera is employed to measure the combustion behavior based on natural luminosity (NL). Proper orthogonal decomposition (POD) is applied to reconstruct and analyze the images. The POD-based coefficient of variation (COV) is implemented to evaluate the cyclic variability, along with the pressure-based and global intensity-based COV. This coefficient is then adopted to discriminate the coherent and incoherent parts from the fluctuations in the luminosity field. The POD-based and global intensity-based COV presents the variations in the luminosity field, which can provide information on chemical kinetics, while pressure-based COV provides a general description of the cyclic fluctuation of thermodynamics. To extract more information from the NL images, the color-intensity COV analysis based on the intensity separated from RGB channels is adopted to estimate the CCVs from the aspect of spectral emissions (excited and ionized radicals in the flame). Finally, the effects of methane lambda, pilot fuel rate and charge air temperature on the CCVs were analyzed systematically. The results revealed that richer methane conditions has an inhibitive effect on the CCVs. The appearance of the CCVs were determined by the ignition characteristics of the pilot fuel. A critical point was found in charge air temperature, when the charge air temperature lower than the critical point, the increase of the charge air temperature has a promotive effect on the CCVs; after that, it has an inhibitive effect on the CCVs.Peer reviewe

Simultaneous Visualization of Natural Luminosity and Chemiluminescence of Dual Fuel Combustion in an Optically Accessible Engine

The engine fueled with methane/diesel is a promising and highly attractive operation mode due to its high performance-to-cost ratio and clean-burning qualities. However, the combustion process and chemical reactions in dual fuel combustion are highly complex, involving short transient pilot-fuel injection into the premixed gaseous fuel charge, autoignition, and combustion mode transition into premixed flame propagation. The motivation of the current investigation is to gain an insight into the combustion dynamics in dual fuel combustion engine based on chemical radicals and thermal radiation. The chemiluminescence (CL) and natural luminosity (NL) are expected to provide specific characteristics in combustion control and monitoring. To visualize the highly unsteady combustion process in terms of OH∗, CH2O∗ radicals and natural luminous emissions, the band pass filters with 308 nm, 330 nm combined with an image doubler are employed to visualize the OH∗ and CH2O∗ CL simultaneously. High speed natural luminosity imaging is adopted to illustrate the effects methane lambda and pilot ratio on the ignition delay, luminous intensity and engine performance. Spectroscopy analysis based on OH∗, CH2O∗ and NL was performed to study the chemical reactions in dual fuel mode.Peer reviewe

HVO, RME and diesel fuel combustion in an optically accessible compression ignition engine

The current paper investigates the spray and combustion characteristics of hydrotreated vegetable oil (HVO), petrol diesel (EN590), blends of HVO with petrol diesel (70% EN590 and 30% HVO), and rapeseed oil methyl esters (RME) in an optically accessible compression ignition engine. Mie scattering and natural luminosity imaging are employed to measure the liquid spray and combustion behaviors. The spray and combustion processes are divided into four stages based on optical imaging. The morphology and quantitative analysis based on imaging provides a method for visualizing the in-cylinder spray and combustion behavior with four test fuels. The ignition delay and combustion characteristics detected from optical measurements are compared to those determined from cylinder pressure. The results show that the ignition delay of HVO and RME occurs earlier and the flame propagation at the premixed combustion stage proceeds faster compared to EN590 and HVO30. The spray and combustion characteristics of HVO30 are similarto EN590. However, ignition occurs earlier for HVO30 due to the higher CN. Comparison of the HVO and RME shows that there is a marginal difference in the ignition delay for these two fuels. However, the combustion duration of RME is shorter than that of HVO.Peer reviewe