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To explore the influence of fuel injection strategy on the combustion process, the Computational Fluid Dynamics (CFD) simulations were performed, and simulation results were validated against the experimental data measured at different rail pressures and injection timings. The experiments were conducted on a diesel engine equipped with an advanced injection system that allows full control over the injection parameters. To model the combustion process of EN590 diesel fuel, two different approaches were used: the General Gas Phase Reactions (GGPR) approach and the 3-zones Extended Coherent Flame Model (ECFM-3Z+). The calculated results, such as mean pressure and rate of heat release, were validated against experimental data in operating points with different injection parameters in order to prove the validity of spray and combustion sub-models. At the higher injected pressure, GGPR model showed better prediction capability in the premixed phase of combustion process, compared to the ECFM-3Z+ model. Nevertheless, in the rate-controlled phase of combustion process, ECFM-3Z+ model shows stronger diffusion of temperature field, due to the more detailed consideration of combustion diffusion phenomena in the ECFM-3Z+ governing equations. Furthermore, the results show that the rail pressure has a lower impact on the combustion process for injection timing after the Top Dead Centre (TDC). Both, single and multi-injection cases are found to be in a good agreement with the experimental data, while the GGPR approach was found to be suitable only for combustion delay determination and ECFM-3Z+ also for the entire combustion process.

The paper presents a first comparative analysis of emission formation phenomena of three different bioliquids, derived from low-cost waste streams while utilizing the same gas turbine-based experimental setup. A consistent and unbiased comparison is ensured by the application of the same experimental test rig featuring only those minor fuel-based adaptations, which are required to ensure the most favorable operation of each of the analyzed fuels. This provides the direct comparative data between combustion performance of liquefied wood, obtained through solvolysis process, glycerol, and waste liquor from nanocellulose production which were previously tested in various combustion systems, hence making a direct evaluation of fuel's suitability difficult. The study focuses on the analysis of all key thermodynamic parameters and significant emission species covering CO, NOx, HC particulate matter, and soot as well as identification of underlying phenomena for observed emission trends. These indicate that for NOx emissions, a good correlation exists to the stoichiometric ratio of the fuels, where a low stoichiometric ratio results in lower NOx emissions, provided that oxygen content is the main diluent and fuel-bound nitrogen is low. As all tested fuels feature oxygen content above 43%, this enables a large improvement in NOx-CO trade off, as CO emissions are reduced with higher peak combustion temperatures while minimally increasing NOx emissions. Similar observations are made for particulate matter–NOx trade off; however, the ash content significantly impacts the particulate matter emission, hence reducing the potential for clean combustion of waste liquor. In the case of glycerol with no ash content, soot emissions are minimal and for an order of magnitude lower than for benchmark diesel fuel, as there are numerous phenomena effectively reducing their formation and increasing their oxidation. The presented research confirms that utilization of bio-intermediates and waste-derived fuels in appropriate combustion setups can, beside a low CO2 footprint, feature also very low emissions of other pollutant species, providing that fuels feature high oxygen content, low ash content, and low nitrogen content. With such approach, it is possible to achieve clean combustion that is fully in line with circular economy guidelines.

High temperature polymer electrolyte membrane fuel cells (HT-PEMFCs) are a promising and emerging technology that allow for highly efficient low emission small scale electricity and heat generation. Simultaneous reduction of production costs and prolongation of the service life is considered as a significant challenge towards their wider market adoptions, which calls for application of predictive virtual tools during the development process of HT-PEMFC systems. To present a significant progress in the addressed area, this paper presents an innovative modelling framework based on: a) mechanistically based spatially and temporally resolved HT-PEMFC performance model and b) modular degradation modelling framework based on interacting partial platinum degradation mechanisms. Proposed innovative tool chain thus allows for - compared to the current state of the art – more efficient and systematic model supported design of FCs and in-depth understanding of cause and effect chain from FC operation to its degradation. This merit of the proposed modelling framework arises from systematic reflection of FC control parameters in operational parameters of the FC, which are inputs to degradation modelling framework that considers in an interacting manner carbon and Pt oxidation phenomena and Pt dissolution, redeposition, detachment and agglomeration phenomena thereby adequately modelling the causal chain.

In the presented study, low temperature combustion was established with a direct injection of diesel fuel being a representative of high reactivity fuels and tire pyrolysis oil being a representative of low reactivity fuels. Tire pyrolysis oil was tested as a potential waste derived fuel for low temperature combustion, as it features diesel-like physical properties and lower cetane number compared to diesel fuel. The goal of this study was determination of suitable injection strategies and exhaust gas recirculation rates to explore potentials of both fuels in reducing emissions in low temperature combustion modes. It was demonstrated that relatively small changes in the engine control strategy possess the potential to significantly improve nitrogen oxide/particulate matter trade-off with minor effect on engine efficiency. In addition, low temperature combustion was for the first time successfully demonstrated with tire pyrolysis oil fuel, however, it was shown that lower reactivity of the fuel is by itself not sufficient to improve nitrogen oxide/ soot trade-off compared to the diesel fuel as entire spectra of fuel properties play an important role in improving nitrogen oxide/soot trade-off. This study thus establishes relations between different engine control strategies, intake manifold pressure and exhaust gas recirculation rate on engine thermodynamic parameters and engine-out emissions while utilizing innovative waste derived fuel that have not yet been analysed in similar combustion concepts.

Increased public concerns and stricter regulatory frameworks promote the role of bioliquids (liquid fuel for energy purposes other than for transport, including electricity and heating and cooling, produced from biomass). This is a driving force for development and employment of micro-gas turbines (MGTs) due to their ability to combust bioliquids with less favorable properties in a decentralized manner. Gas turbines are characterized by relatively high combustion efficiency at relatively low concentrations of harmful emissions, relatively high effective efficiency and durability when utilizing a common portfolio of gas turbine approved fuels. It is thus desired to preserve these advantages of gas turbines also while burning bioliquids and further relying on their scalability that is crucial to efficient support of decentralized energy production at small scales. To support these objectives, MGT technology needs to allow for utilization of bioliquids with much wider spectrum of physical and chemical properties compared to common commercially available MGTs in a single MGT-based plant. In this view, the present study is providing the first thorough overview of challenges and solutions encountered by researchers across the wide area of bioliquids in MGTs.

This study proposes a novel methodology for designing an optimum equiripple finite impulse response (FIR) filter for processing in-cylinder pressure traces of a diesel internal combustion engine, which serve as inputs for high-precision combustion analyses. The proposed automated workflow is based on an innovative approach of determining the transition band frequencies and optimum filter order. The methodology is based on discrete Fourier transform analysis, which is the first step to estimate the location of the pass-band and stop-band frequencies. The second step uses short-time Fourier transform analysis to refine the estimated aforementioned frequencies. These pass-band and stop-band frequencies are further used to determine the most appropriate FIR filter order. The most widely used existing methods for estimating the FIR filter order are not effective in suppressing the oscillations in the rate- of-heat-release (ROHR) trace, thus hindering the accuracy of combustion analyses. To address this problem, an innovative method for determining the order of an FIR filter is proposed in this study. This method is based on the minimization of the integral of normalized signal-to-noise differences between the stop-band frequency and the Nyquist frequency. Developed filters were validated using spectral analysis and calculation of the ROHR. The validation results showed that the filters designed using the proposed innovative method were superior compared with those using the existing methods for all analyzed cases. Highlights • Pressure traces of a diesel engine were processed by finite impulse response (FIR) filters with different orders • Transition band frequencies were determined with an innovative method based on discrete Fourier transform and short-time Fourier transform • Spectral analyses showed deficiencies of existing methods in determining the FIR filter order • A new method of determining the FIR filter order for processing pressure traces was proposed • The efficiency of the new method was demonstrated by spectral analyses and calculations of rate-of-heat-release traces

This study investigates for the first time the combustion in a micro gas turbine (MGT) of a new bioliquid, a viscous biocrude, which is a liquefied wood (LW) produced via solvolysis of lignocellulosic biomass in acidified glycols. The test rig includes a modified fuel injection line, a re-designed combustion chamber and revised fuel injection positions. The main novelties of this work are: (1) producing of liquefied wood with pure ethylene glycol as a solvent, and methanesulfonic acid as a catalyst, to obtain a bio-crude with lower viscosity and higher lignocellulosics content than previous tested formulations; (2) upgrading raw liquefied wood by blending it with ethanol to further reduce the viscosity of the mixture; (3) utilizing a commercially available MGT Auxiliary Power Unit (APU) of 25 kW electrical power output, with notably reduced extent of adaptations to use the newly obtained fuel mixture. Fuel properties, and their impact on combustion performance using liquefied wood, are investigated by analyzing MGT performance and emissions response at different load and blend ratios. Emissions revealed that the presence of LW in the blends significantly affects CO and NOX concentrations compared to conventional fuels. CO roughly increased from 600 ppm (pure ethanol as fuel) to 1500 ppm (at 20 kW electrical power). The experimental study reveals that it is possible to achieve efficient MGT operation while utilizing high biocrude to ethanol ratios, but a number of adaptations are necessary. The achieved maximum share of liquefied wood in the fuel blend is 47.2% at 25 kW power output. Main barriers to the use of higher share of liquefied wood in these type of systems are also summarized.

Air quality in urban areas is strongly influenced by exhaust emitted by the public transport fleet. The aim of this study was to analyze benefits in the fuel consumption, fuel costs and exhaust emissions when replacing baseline diesel fueled EURO III city buses by the compressed natural gas (CNG)-fueled EURO V buses and by hydraulic series hybrid diesel-fueled EURO V buses. Real-world measurements were performed on the regular bus route to access realistic energy consumption and exhaust emissions. Instantaneous gaseous emission (CO$_2$, CO, NO$_x$ and THC) were measured together with the instantaneous PM$_{10}$ mass emission. Innovativeness of the presented approach thus arises from the systematic comparison of different powertrain technologies under real-world drive cycles and measuring time traces of not only gaseous but also of PM$_{10}$ mass emissions. Furthermore, lumped cycle averaged emissions are interpreted and explained by typical powertrain performance parameters and exhaust emission time traces. Cumulative results indicate that application of the CNG fueled buses does not necessary reduce CO$_2$ emissions compared to diesel-fueled buses whereas reduction in fuel costs is evident. Additionally, it is shown that hybrid operation of the hydraulic series hybrid diesel-fueled bus resulted in higher fuel consumption due to poorly optimized hybrid topology and control strategy. Furthermore, analyses of the time traces point out inadequate lambda control of CNG-fueled buses and nucleation mode-based particle number emissions during deceleration.

The paper outlines a procedure for the computer-controlled calibration of the combined zero-dimensional (0D) and one-dimensional (1D) thermodynamic simulation model of a turbocharged internal combustion engine (ICE). The main purpose of the calibration is to determine input parameters of the simulation model in such a way as to achieve the smallest difference between the results of the measurements and the results of the numerical simulations with minimum consumption of the computing time. An innovative calibration methodology is based on a novel interaction between optimization methods and physically based methods of the selected ICE sub-systems. Therein physically based methods were used for steering the division of the integral ICE to several sub-models and for determining parameters of selected components considering their governing equations. Innovative multistage interaction between optimization methods and physically based methods allows, unlike the use of well-established methods that rely only on the optimization techniques, for successful calibration of a large number of input parameters with low time consumption. Therefore, the proposed method is suitable for efficient calibration of simulation models of advanced ICEs.

Tire pyrolysis oil (TPO) represents a promising waste-derived fuel for Diesel engines with its main deficiency being lower cetane number compared to Diesel fuel. Until now, successful utilization of the TPO in Diesel engines was possible only by increasing its cetane number, increasing compression ratio of the engine or preheating intake air or operation. This study shows the foremost results of utilizing the pure TPO in a modern turbocharged and intercooled Diesel engine without any of the aforementioned aids, which significantly facilitates its use and boosts its conversion efficiency to mechanical work. This was achieved by the tailored injection strategy that includes pilot injection, which was previously not utilized in combination with the TPO. The study reveals that with additional tailoring of the pilot injection, further optimization of thermodynamic parameters can be achieved while operating the turbocharged and intercooled Diesel engine in a wide operating range under the use of pure TPO. Discovered phenomena are supported by interpretation of interactions between the injection parameters and combustion as well as emission formation phenomena of the pure TPO.