Low Temperature Combustion Research Articles

Optical and Numerical Investigations on Combustion and OH Radical Behavior Inside an Optical Engine Operating in LTC Combustion Mode

Low Temperature Combustion (LTC) is a relevant process for internal combustion engines (ICE). This combustion mode is based on premixed fuel/air and fuel lean in-cylinder mixture allowing reduction in NOx and PM emissions while maintaining higher thermal efficiency. In order to investigate the effect of engine operating conditions on the behavior of LTC mode, including OH radical evolution, optical measurements and numerical simulations were performed on a transparent CR diesel engine. The homogeneity of the engine charge was obtained by using very early injection timings. In this study, varying injection strategies were investigated for different engine speeds. In parallel to the experimentation, simulations of LTC mode for the same experimental operations were carried out. The model used in this study is based on a stochastic reactor model. This model includes a turbulence (k-ε) model based on a zero-dimensional energy cascade to calculate the turbulent time scale during the cycle. On the other hand, due to the stochastic approach and to reduce initial heterogeneities of the mixture, a confidence parameter was introduced in the global model to consider the real variation ranges of engine. This latter was modeled as a function of the Reynolds number allowing to initiate heterogeneities of temperature and of species mass. OH radicals were estimated with high spatial and temporal resolution using chemiluminescence measurements. Simulated in-cylinder pressure and the OH radical rate were compared to the experimental data. A good agreement was observed in terms of in-cylinder pressure trace and ignition delay times, meaning that the confidence coefficient model is accurate to describe the initial heterogeneities of the mixture. The simulated OH rate profile has the same shape as the measured OH trace and the main ignition occurs at the same time. This study corroborates that the OH radical is an appropriate tool to identify combustion stages.

Low-temperature catalytic combustion of trichloroethylene over MnO -CeO2 mixed oxide catalysts

The cerium-based catalysts were investigated for the catalytic combustion of trichloroethylene (TCE) and exhibit a surprising catalytic activity. MnOx was doped into CeO2 by a citric acid (CA) sol-gel method, and the effect of Mn content on the physicochemical properties and catalytic activities of MnOx-CeO2 mixed oxides was investigated systemically. The introduction of MnOx into CeO2 can evidently improve the catalytic activity and reaction stability of the CeO2 catalyst, and the catalytic activity can be maintained for more than 100 h at 250 °C under air atmosphere. Moreover, a possible reaction mechanism and a catalytic cycle for the catalytic combustion of TCE over the MnOx-CeO2 mixed oxide catalysts are proposed.

A Review on Recent Developments of RCCI Engines Operated with Alternative Fuels

Environmental concerns over automotive exhaust emissions and consumer demand for higher fuel efficiency have led to the development of low-temperature combustion concepts. The reactivity-controlled compression ignition (RCCI) engine is one among them and has the potential to reduce NOx and smoke emissions simultaneously. In this concept, a low-reactivity fuel is injected into the intake port and another high-reactivity fuel is injected into the cylinder directly. This results in reactivity stratification and provides more control over the rate of heat release. However, operating parameters such as reactivity of fuels, premixing ratio, injection strategies, exhaust gas recirculation ratio, piston bowl geometry, and compression ratio influence emissions formation. The article reviews recent developments on the effect of the above operating parameters on the performance and emission characteristics of RCCI engines operated with alternative fuels. The combustion strategies used to extend the RCCI mode to higher loads are also reviewed. Applications of computational fluid dynamics (CFDs) to design the combustion chamber for RCCI engines are discussed. The need for further improvements in the CFD models for RCCI engines is explained. After presenting a thorough review of recent literature, directions for future research on RCCI engines are proposed.

Effects of injection parameters and intake air temperature on acetone-butanol-ethanol (ABE) blend HCCI-DI engine

Homogeneous charge compression ignition-direct injection (HCCI-DI) approach was reported to effectively eliminating the problems associated with HCCI engine while promoting HCCI combustion. Acetone-butanol-ethanol (ABE) fuel has been studied previously to replace butanol due to its lower production cost and time. This paper aims to extend the potentials of ABE fuel in HCCI-DI engine with other parameters such as intake air temperature, port injection timing and port injection pulse width also investigated. Diesel, ABE5 (5 % ABE and 95 % diesel by vol.) and ABE10 (10 % ABE and 90 % diesel by vol.) were used with different engine loads (1 Nm, 2 Nm, 3 Nm, 4 Nm and 5 Nm). Further experiments were carried out using ABE10 with different intake temperatures (60 °C, 80 °C, 100 °C, 120 °C and 140 °C), port injection timings (230 °CA BTDC, 250 °CABTDC, 270 °CA BTDC, 290 °CA BTDC and 310 °CA BTDC) and port injection pulse widths (3 ms, 4 ms and 5 ms). It was found that increasing ABE ratio reduces the brake specific fuel consumption (BSFC) and increases the brake thermal efficiency (BTE) of the HCCI-DI engine. Up to 13.55 % and 23.8 % BTE improvement when ABE5 and ABE10 were used compared to diesel respectively. Furthermore, increasing the port injection pulse width increased the BSFC and reduced the BTE significantly by 10 % on average. Compared to diesel, ABE5 reduced the NOx emission by 20.2 % on average while NOx reduced by 24.8 % when ABE10 was used. Increasing the intake air temperature more than 100 °C significantly increased NOx by 54.1 % while HC decreased up to 23.2 % with 140 °C intake air temperature. Advanced port injection timing reduced the NOx emission by up to 24.7 %. NOx emission was reduced by 12.5 % as the pulse width increased from 3 ms to 5 ms due to higher premixed ratio combustion leading to lower combustion temperature. The combustion phasing of the engine was sensitive to the variation of intake temperature resulting in advanced start of combustion as the intake temperature increased. Besides, the combustion phasing reported to be steadily advanced as the pulse width increased which is showing its sensitivity towards the amount of port fuel injected. In conclusion, it was shown that ABE fuel is not only renewable but also capable of reducing emission without compromising the engine performance of HCCI-DI engine.

3D porous nanostructured reduced graphene oxide and nafion composite as an ultrasensitive interface for rapid and nanomolar determination of a flavonoid, galangin

Graphene-based nanostructures are considered ideal modifiers for electrochemical sensors owing to their unique structural, conductive, and catalytic properties. Given this, herein we have developed a three-dimensional reduced porous graphene oxide-nafion nanocomposite film modified glassy carbon electrode (p-rGO/NAF/GCE) for electrochemical determination of a flavonoid, galangin (GAL) for the first time. A simple, almost instantaneous, and environmentally benign “low-temperature solution combustion” method was used for the preparation of p-rGO using glycine as a fuel and green reducing agent simultaneously, followed by compositing it with nafion and coating on GCE to form an electrochemical sensor. The p-rGO/NAF/GCE promoted the mass transfer of GAL to the electrode surface and exhibited excellent electrocatalytic activity towards the oxidation of GAL with a significant enhancement (∼70-fold) in the peak current. The enhanced electrocatalytic activity was attributed to the synergistic contribution from p-rGO and nafion, which provided higher active surface area, porous network structure, feasible cation exchangeability, and strong adsorption capacity. The two anodic peaks exhibited by GAL at p-rGO/NAF/GCE involved an equal number of protons and electrons via diffusion-controlled (peak a1) and adsorption-controlled (peak a2) processes. Linear response over concentration range of 1.99 × 10−8 – 4.5 × 10−5 mol L−1 of GAL was established with the lowest limit of detection value of 1.11 nM by square wave voltammetric (SWV) method. Importantly, the fabricated sensor demonstrated repeatability, high stability, and potential anti-interference properties with practical utility for the analysis of analyte-fortified biological samples and pharmaceutical formulations with good recoveries.

Investigative research of diesel/ethanol advanced combustion strategies: A comparison of Premixed Charge Compression Ignition (PCCI) and Direct Dual Fuel Stratification (DDFS)

Direct Dual Fuel Stratification (DDFS) is a new low-temperature combustion (LTC) approach that employs dual fuel direct injection in the combustion chamber. In this method, a relatively small proportion of diesel fuel was pre-injected and utilized to activate the burning of the premixed charge followed by direct injection of a diesel/ethanol mixture (75% diesel, 25% ethanol by volume) into the combustion chamber near TDC. The DDFS approach generates a lower reactivity charge in the central sector of the combustion chamber and a stronger reactivity charge along the wall. For the examination of combustion vibrations and acoustic, a new technique dependent on the fast Fourier transform (FFT) of the cylinder vibration statistics was used. Whereas the PCCI combustion technique is more likely to cause knocking than the typical diesel CI, the results show that charge stratification in DDFS combustion does have a good effect in reducing vibration intensity. Owing to the improved controllability of the start of combustion and burning period, DDFS combustion attained a brake thermal efficiency (BTE) of 51%, which was larger than CI and PCCI. DDFS shows ultra-low nitrogen oxide (NOx) (below 1 g/kW-h), mild carbon monoxide (CO) (below 6 g/kW-h), and unburned hydrocarbons (UHC) emissions. Because of the higher thermal efficiency and a decreased carbon source due to presence of ethanol, DFFS combustion could produce lower CO levels by up to 34% when compared to PCCI.

Ranking of four dual loop EGR modes

Modern Diesel engines contain sophisticated control systems to keep their environmental impact low for sustainable road transport. One of these systems is the dual loop exhaust gas recirculation, which can change combustion properties in several ways. This article presents an engine dyno measurement based on analyzing the duel loop EGR with a medium-duty Diesel engine. Intake throttles and exhaust brakes for the highest freedom in the air-fuel ratio setting support the EGR systems. The EGR modes are compared from fuel consumption, NOx emission, and exhaust gas opacity in steady and transient operations. There are expected results, for instance, in the HP EGR’s faster reaction time or the LP EGR’s boost pressure holding property. Unexpected results are also presented. Contrary to theory, LP EGR generally provides a fuel consumption advantage in many operation points due to its higher boost pressure. Typically, HP EGR can provide lower fuel consumption at higher engine power. In the emission results, LP EGR is favourable both in NOx emission and exhaust gas opacity, whereas the intake throttle-supported HP EGR usually shows the highest emission. Besides, with high EGR rates at lower engine loads, LP EGR can realize low-temperature combustion, where both emissions decrease. No difference can be detected between the LP EGR’s support valves’ results. HP EGR was faster in the transient operation, with about half the reaction time. The results can be utilized for dual-loop EGR layout and control design.

Theoretical study on the reaction kinetics of CO oxidation by nitrogen-doped graphene catalysts with different ligand structures

Harmful carbon monoxide (CO) gas from vehicle exhaust and fossil fuel combustion seriously affects the ecological environment and human health, although this issue can be effectively solved by low-temperature catalytic combustion. Herein, an Fe and N codoped double vacancy graphene catalyst (Fe-CxNy) for the low-temperature catalytic combustion of CO is proposed, and the mechanism of the CO catalytic combustion reaction over the catalyst is systematically investigated by using density function theory (DFT). Four oxidation mechanisms, including Eley–Rideal (ER1 and ER2), Langmuir-Hinshelwood (LH) and Termolecular Eley–Rideal (TER), were compared in terms of oxidation pathways and energy distribution. All the results indicate that Fe-CxNy catalysts have efficient catalytic activity. The Fe-CN3 catalyst with the predominant LH reaction mechanism showed the best performance for the catalytic combustion of CO with only 0.20 eV, which was comparable to that of noble metals. The rate constant calculations further demonstrate that Fe-CN3 exhibits excellent catalytic performance at low temperatures. This work not only provides a theoretical basis for the design and development of low-temperature catalytic combustion CO catalysts, but also provides data support for the kinetic model of CO combustion reaction.

A Comprehensive Review of the Free Piston Engine Generator and Its Control

Review A Comprehensive Review of the Free Piston Engine Generator and Its Control Patrick Brosnan 1, Guohong Tian 1, * , Umberto Montanaro 1, and Sam Cockerill 2 1 School of Mechanical Engineering Sciences, University of Surrey, Surrey GU2 7XH, UK 2 Libertine FPE Ltd., Sheffield S9 1DA, UK * Correspondence: g.tian@surrey.ac.uk; Tel.: +44-1483-300-800 Received: 2 February 2023 Accepted: 10 March 2023 Published: 23 March 2023 Abstract: The Free Piston Engine (FPE) is a unique machine with a higher thermal efficiency than its counterpart, the Conventional Reciprocating Piston Engine (CPE). The unique piston motion of the FPE is not constrained kinematically like the CPE with its connecting crankshaft and rotational inertial masses. Moreover, when directly coupled to the Linear Electric Machine (LEM) to harness electric energy production, the Free Piston Engine Generator’s (FPEG) characteristic motion, now being dynamically constrained, permits an extensive range of piston trajectory profiles to be exploited during operation. In addition, exploring varied piston trajectories during the development stages may be vital in reducing in-cylinder combustion emissions through strategies such as Low-Temperature Combustion (LTC) and Homogeneous Charge Compression Ignition (HCCI). This review paper will focus on the key motivations and drivers for continued FPEG development. It will also highlight and review its distinct advantages and challenges in being a viable solution as a future zero-carbon engine technology. Finally, FPE fundamentals, alongside its rich history, will be introduced, clearly presenting how academia and industry have described and controlled its intrinsic non-linear dynamics.

Low-temperature gas-phase toluene catalytic combustion over modified CoCr2O4 spinel catalysts: Effect of Co/Cr content and calcination temperature

Un-supported spinel-type cobalt chromite catalysts were synthetized by propionic acid-mediated sol-gel method and tested for toluene oxidation. The influence of the Co and Cr content and the preparation conditions on physico-chemical, surface and catalytic properties for this reaction has been for the first time evaluated. Co-rich CoCr2O4 was the most active catalyst, likely due to the formation of a single CoCr2O4 spinel phase, a favorable surface composition and higher low-temperature reducibility. Besides, the increase of the calcination temperature, despite worsening textural properties, also has a promoting effect on the catalytic activity by preserving a suitable reducibility and further enhancing the surface properties. Surface Cr6+ ions and adsorbed oxygens (Oads), which are more abundant in the most efficient catalyst (Co-rich catalyst calcined at 685 °C), seem to play an important role on toluene oxidation reaction. These findings may open potential strategies in the development of efficient and economically competitive catalysts for elimination of VOCs like toluene.

A mechanic insight into low-temperature catalytic combustion toward ethylene oxide over Pt-Ru/CuCeOx bimetallic catalyst

The catalytic oxidation performance toward ethylene oxide (EO) and the consequent mechanism were investigated on the Pt-Ru/CuCeOx bimetallic catalyst, which was prepared by a distinct method combining stepwise adsorption and subsequent impregnation. The catalytic tests show that the introduction of Ru into the Pt catalyst, so as to form Pt-Ru bimetallic active sites, can greatly increase the oxidation activity of the catalyst, as evidenced by the extremely lower full oxidation temperature (120 °C) when compared with that of the Pt/CeO2 catalyst (160 °C). The XPS spectra show that the Ru species (mainly RuOx) have strong interaction with the CuCeOx support, which can therefore affect the electron transfer between the Pt species and the support. As a result, the oxygen activation on Pt species is obviously facilitated and catalytic activity is enhanced. Finally, in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTs) was used to track the reaction mechanism. It is found that the catalytic oxidation process follows the MvK catalytic mechanism at low temperature and the L-H catalytic mechanism when the temperature moves to higher range.

Parametric optimization with Biodiesel-water emulsion under premixed lean combustion to achieve high efficiency and clean combustion

Advanced low temperature combustion (LTC) aids in simultaneously controlling exhaust emissions of oxides of nitrogen (NOx) and particulate matter (PM). However, LTC strategies are constrained by achievable load range restriction and higher levels of unburned hydrocarbon (HC) and carbon monoxide (CO). The present investigation envisages combining renewable biodiesel-water emulsions and an advanced premixed lean combustion strategy to curtail the higher HC and CO emissions without sacrificing engine performance. Non-edible Karanja oil was the source of biodiesel and the emulsion stabilizer. A production light-duty diesel engine is modified to run under premixed lean combustion conditions based on late injection using a fully-flexible electronic fuel injection system. The engine operating parameters were optimized, including fuel injection timing, EGR flow rate, and emulsion water concentration. Emulsions of neat biodiesel were prepared to contain 6, 12, and 18% water on a mass basis using 1 and 2% surfactant by mass. The fuel injection timing was varied from 2 to 4 degrees after the top dead centre, and up to 15% EGR flow rate was utilized. Design of experiments aided in minimizing the number of engine tests. The performance and emission parameters were the output responses. Taguchi Grey Relational Analysis established the optimal combination of input factors to improve engine performance and reduce exhaust emissions. Engine experiments at optimized operating conditions revealed that compared to conventional diesel combustion, the brake thermal efficiency and brake specific fuel consumption improved by 33 and 16%, respectively, at 5.08 bar BMEP. The NOx, smoke and HC emissions were reduced by 68, 73 and 46%, while CO emissions increased nearly two-fold.

Effect of microwave pretreatment on oxidization behaviors of bituminous coal: Experimental measurement and quantum chemistry calculation

The poor heat conduction and mass transfer of coal seam causes unsatisfying performance of gas production for in situ combustion, while microwave pretreatment is a promising technology to solve this problem. In this work, microwave heating is adopted as pretreatment method to prepare coal samples at different microwave time. The low temperature oxidization and high temperature combustion behaviors of raw coal and modified coal samples were studied with programmed temperature rising method. The functional group content in coal samples were measured with Fourier transform infrared spectrometer, while the relationship between microstructure and reactivity was studied with quantum chemistry calculation. As microwave heating time extends from 0 s to 180 s, the crossing point temperature decreases, while the combustion reaction rate increases. As microwave time prolongs from 180 s to 240 s, the crossing point temperature becomes larger, while the combustion reaction rate becomes smaller. As microwave time increases from 0 s to 240 s, hydroxyl content and carbonyl content in coal samples reduce while ether content rises. The reduction of hydroxyl and increase of ether result in an enhancement of oxidization reactivity. The decrease of carbonyl is unfavorable for oxidization reactivity. Therefore, the effect of microwave heating on coal reactivity has two sides. This explains why the microwave pretreatment time has a non-monotonic effect on the coal reactivity in both low temperature and high temperature range.

Ignition and stabilization of laminar premixed n-heptane/air flames under engine-like conditions

The multi-stage ignition process of a laminar premixed n-heptane/air mixture is investigated under engine-relevant conditions. The cold fuel/air mixture is injected into a hot environment through an inflow boundary at different inlet velocities. Results show that a double-flame structure for stoichiometric mixture is observed and it transitions to a single flame at an inlet temperature (TFuel) of 700 K. The cool flame is stabilized near the inlet for the case with TFuel = 900 K before the hot flame merging with it. However, both the cool and hot flames move upstream for TFuel = 800 K due to the negative temperature coefficient (NTC) behavior. In addition, the effect of inlet velocity is also studied. By increasing the inlet velocity, the hot flame becomes lifted off. Comparisons of the ignition Damkӧhler number (Daign) defined by the ratio of the residence time to the cool- or hot-flame IDTs illustrate the different controlling mechanisms. At a low temperature of 700 K, both low-temperature combustion (LTC) and high-temperature combustion (HTC) have a Daign value of unity, indicating that the stabilization process is mainly controlled by autoignition rather than diffusion. The heating effect from the hot environment enhances the NTC characteristics of the premixed flame, thus, shortening the IDT. Whereas at 800 K, the value of Daign for the LTC is of unity, but that of HTC decreases, especially at a low inlet velocity, indicating that diffusion plays a more important role for HTC and the flame is stabilized by propagation, which can also be confirmed from the comparisons of the 0-D and 1-D ignition delay times (IDTs). Diffusion of intermediate radicals and heat suppresses the appearance of the high-temperature ignition at an inlet velocity of 1 m/s. At 900 K, high inlet velocity can increase the Daign to unity, indicating a transition in the combustion regime from propagation to autoignition.

Experimental Evaluation of Pilot and Main Injection Strategies on Gasoline Compression Ignition Engine—Part 2: Performance and Emissions Characteristics

<div>Internal combustion (IC) engines play an important role in the global economy by powering various transport applications. However, it is a leading cause of urban air pollution; therefore, new combustion strategies are being developed to control emissions. One promising advanced low-temperature combustion (LTC) technology is gasoline compression ignition (GCI). This experimental study assesses the performance of a two-cylinder engine, emissions, and exhaust particulate characteristics using G80 (80% v/v gasoline and 20% v/v diesel) blend operating in GCI mode vis-à-vis baseline conventional diesel combustion (CDC) mode using diesel. The effects of double pilot injection, Pilot-1 proportion (10–30%), and main injection timing were investigated on the GCI combustion. Experiments were performed at different engine loads (3, 4, and 5 bar brake mean effective pressure [BMEP]) at a constant engine speed (2000 rpm). GCI combustion showed higher brake thermal efficiency (BTE) than CDC mode at medium loads. Hydrocarbon (HC) and carbon monoxide (CO) emissions increased in GCI mode, but oxides of nitrogen (NOx) were reduced than the baseline CDC mode. High pilot ratio and late main injection timing tests showed higher HC and CO emissions in the GCI mode at low engine loads. The GCI mode engine emitted higher nucleation mode particles and nanoparticles than baseline CDC mode at high engine loads. Using a triple injection strategy, GCI engines simultaneously reduced NOx and particulate matter (PM) emissions, especially at high loads. Controlling these emissions in baseline CDC mode engines is otherwise quite challenging.</div>

Analysis of combustion cyclic variation in a lean burn spark-ignited engine using large eddy simulation

The low-temperature combustion technique improves engine efficiency by reducing the thermal and exhaust losses. The representative method of low-temperature combustion technique is lean burn. However, lean burn has been limited because it increases the cycle-to-cycle variation (CCV) owing to poor initial ignition stability. To overcome the low initial ignition stability, increasing the spark energy intensity and strengthening the tumble motion have been proposed. Therefore, lean burn engines with ignition stability are being rapidly developed recently. In this study, the result of the LES simulation of a lean burn engine showed the importance of ignition delay increased more than that of a conventional gasoline engine. With the importance of ignition delay in lean burn condition, the sources of the ignition delay were analyzed. The primary ignition delay sources were the flow velocity near the spark plug and the subgrid-scale turbulent kinetic energy. Next, the parameters affecting the 5% mass fraction burned (MFB) duration were analyzed by comparing five characteristic cycles. Also, factors that decreased the correlation coefficient were analyzed by comparing with the outlying cycle. As a result of analyzing the cycle with a significant change in MFB 5 and MFB 50 ranking, the burn duration was found to be affected by curl TKE, SGS TKE, large-scale flow motion, and air–fuel ratio. Finally, methods to reduce CCV were proposed. The first method was to increase tumble X+ and tumble X- using pistons that enhance the wall flow. Consequently, the coefficient of variance (COV) during the ignition delay was reduced by 27%. The second method involved changing the injector target to enhance tumble Y. The enhanced tumble Y reduced the COV of burn duration by 11%.

Power characteristics with different types of turbochargers for lean boosted hydrogen direct injection engine in NOx-free operation

Lean boosting is a low-temperature combustion technology that can contribute to the expansion of the operation range by reducing the pressure increase rate and the combustion temperature owing to the increase in the intake air amount, even though the amount of heat supplied is the same. By optimizing the boosting device of the direct-injection-type hydrogen engine, it was expected that the operating range could be expanded through the torque increase owing to the increase in the amount of heat supplied according to the increase in the intake air mass, and nitrogen oxides emission was expected to be suppressed owing to lean low-temperature combustion. In the present study, to examine the possible output limit of a hydrogen engine under high-lean boosting conditions by applying a boosting device with a different control method, the performance according to the engine speed was observed under the condition of minimizing nitrogen oxide emission. Owing to the boosting performance by the variable turbocharging device, the output power was improved by 165% compared to that of the naturally aspirated-type combustion at a rotation speed of 5000 rpm.

Advanced combustion strategies for improving ic engine efficiency and emissions

The growing need for higher fuel efficiency and compliance with increasingly stringent emission regulations has prompted significant advancements in internal combustion (IC) engine technology. Traditional combustion methods, while widely utilized, face inherent challenges such as limited thermal efficiency and the production of harmful emissions like nitrogen oxides (NOx), particulate matter (PM), carbon monoxide (CO), and unburned hydrocarbons (HC). To address these concerns, researchers and engineers have developed a range of advanced combustion strategies that offer the potential to drastically improve engine efficiency while minimizing environmental impact.This paper provides a comprehensive analysis of cutting-edge combustion techniques, with a focus on strategies that balance the trade-off between fuel efficiency and emission reduction. Prominent among these strategies is Homogeneous Charge Compression Ignition (HCCI), which utilizes a lean, premixed air-fuel mixture to achieve spontaneous ignition at low temperatures, significantly reducing NOx and PM emissions. Another promising technique, Reactivity-Controlled Compression Ignition (RCCI), leverages the controlled use of two fuels with different reactivity levels, enabling precise control over the combustion process and enhancing both fuel efficiency and emission control. In contrast, Gasoline Direct Injection (GDI) technology improves fuel atomization and combustion control by injecting fuel directly into the combustion chamber, leading to higher efficiency and power output, albeit with challenges related to particulate emissions.In addition to these combustion strategies, this paper explores the role of Low-Temperature Combustion (LTC), which operates at reduced in-cylinder temperatures to mitigate the formation of NOx and soot, as well as the potential of advanced ignition systems like plasma or laser-based ignition to improve lean-burn combustion processes. Furthermore, the paper examines the integration of renewable fuels, such as hydrogen and biofuels, with advanced combustion techniques to support the global transition toward cleaner energy.The analysis also considers technological enablers such as variable valve timing (VVT), turbocharging, and sophisticated exhaust after-treatment systems that complement these advanced combustion strategies. Moreover, the application of simulation and optimization tools, including computational fluid dynamics (CFD) and machine learning (ML), is highlighted as essential for refining engine design and optimizing combustion processes.Despite the notable progress, challenges remain in terms of system complexity, control precision, and expanding the operational range of these advanced combustion techniques. As the automotive industry moves towards electrification and hybridization, advanced IC engine combustion strategies will continue to play a crucial role in improving vehicle performance and sustainability. This paper concludes by outlining the future prospects for further optimizing combustion efficiency and integrating renewable fuels in next-generation IC engines, thereby contributing to a cleaner, more efficient transportation sector.

ASSESSMENT OF RIVER SEDIMENT QUALITY ACCORDING TO THE EU WATER FRAMEWORK DIRECTIVE IN LARGE RIVER FLUVIAL CONDITIONS. A CASE STUDY IN THE LOWER DANUBE RIVER BASIN

Increase of pollution of surface water and water sediments with hazardous substances (HSs) in the Danube River Basin requires implementation of systematic monitoring and evaluation of the sediment quality. The present study is focused on the ’South Danube’ Test Area (SDTA) that covers parts of the Lower Danube Basin in Romania, Serbia and Bulgaria. The SD area represents an extended region where Danube reaches its largest widths and depths and where pollution (industrial, mining, agricultural, waste etc.) from tributaries and land is supposed to accumulate in the sediments. Sampling of river bottom sediment (BS), suspended sediment (SS) and overbank (floodplain) sediment at two layers (0-5 cm in the top layer (FS TS) and 40-50 cm in the bottom layer (FS BS)), was carried out at 11 locations in order to analyze the concentration and distribution of 8 metal(oid)s (Cu, Pb, Zn, Cd, Hg, Ni, Cr, As), 6 polycyclic aromatic hydrocarbons (PAHs) and 6 pesticides as hazardous substances. The 2013/39/EU Directive and EU Water Framework Directive standards were used to sediment quality assessment. As a whole, the concentrations of heavy metals in the sediments are comparatively low and are around the normal values for soils. On the other hand, some sampling sites and sediment types have high or very high metal concentrations which exceed intervention levels. Our study well recognizes mining pollution sources in the Danube tributaries Borska Reka, Timok, Ogosta, Malak Iskar and Iskar from past and/or recent mining activity. This pollution is limited to the Danube tributaries and around their confluences into the Danube River. The concentration of heavy metals is strongly diluted in the Danube River and drops around normal values. The studied sediments reveal low concentrations of PAHs. Only fluoranthene content is higher in most of the sediment types and sampling sites on the Danube River, but exceeds the interventional level only at Pristol and at Hârșova. Our results show that the sediments in the Danube River are more polluted with PAHs than its tributaries. The identified organic compounds are assumed to be generated during incomplete or low temperature combustion processes or during road transportation and/or the navigation on the Danube River.

Intensity enhancement of photoluminescence in Tb3+ /Eu3+ co-doped Ca14 Zn6 Al10 O35 phosphor for WLEDs.

This article focuses on the effect of monovalent cation doping on the optical properties of rare earth (RE = Eu3+ , Tb3+ ) co-doped Ca14 Zn6 Al10 O35 which has been synthesized by a low temperature combustion method. Crystalline phase of the Ca14 Zn6 Al10 O35 phosphor was examined and confirmed by X-ray diffraction measurement. Under near-ultraviolet light excitation Eu3+ -doped Ca14 Zn6 Al10 O35 phosphor exhibit characterization of Eu3+ emission bands that are located at a maximum wavelength (λmax ) of approximately 470 nm and other peaks centred at 593 nm and 615 nm, respectively. With Tb3+ -doped Ca14 Zn6 Al10 O35 phosphor showing a green emission band centred at 544 nm under near-ultraviolet range. Furthermore, we studied the energy transfer process in Eu3+ /Tb3+ pair and enhancement in photoluminescence (PL) intensity with doping different charge compensation. Here we obtained the optimum PL emission intensity of the phosphor in broad and intense visible spectral range which may be significant for the fabrication of white light emitting diodes (WLEDs).