Journal of Energy Engineering

The present work attempts to investigate the effect of compression ratio (CR) and injection timing (IT) on the energy and the exergy potential of a biogas-run dual fuel diesel engine. For experimentation, a 3.5 kW single cylinder, four-stroke, direct injection, naturally aspirated, water cooled, variable compression ratio diesel engine is converted into a dual fuel engine. Experiments are conducted for 16 different combinations comprising of ITs of 23, 26, 29, and 32° before top dead center (BTDC) and CRs of 18, 17.5, 17, and 16 at full load condition of 4.24 bar of brake mean effective pressure. The parameters analyzed are the energy and exergy potential of fuel input, shaft work, cooling water, exhaust gas, exergy destruction, peak cylinder pressure, peak heat release rate, brake thermal efficiency, exergy efficiency, exhaust gas temperature and entropy generation rate. The thermodynamic analysis indicates that the combination of IT = 29° BTDC and CR = 18 gives an improved performance of the biogas-run dual fuel diesel engine.

The main scope of the present work is to examine the combustion processes inside the cylinder of a spark-ignition (SI) engine fueled with a methane-hydrogen blend with variable equivalence ratio. This combustion analysis is conducted with a computational fluid dynamics code, which is an in-house code and has been initially developed for simulating hydrogen-fueled SI engines. Lately, its combustion model has been extended with the introduction of methane fuel and various routes are used for the calculation of the nitric oxide (NO) emissions. The first task is to conduct the validation of this code, focusing on this newly developed combustion model. This validation is based on both performance and emissions comparison with experimental data, in order to gain a complete view of the code capabilities. The available experimental data are from a two-cylinder SI engine with complete sets of measured values. For the current study, it was decided to focus on the effect of the equivalence ratio (from 0.7 up to 1), keeping the hydrogen content constant (30% by volume). This comparison revealed that a good match exists for both performance and emissions, showing that the code can be applied for detailed investigation of such combustion processes. A detailed combustion analysis is then conducted, by further processing the results of the numerical code, providing insight of the flame front propagation and NO emissions production inside the engine cylinder.

The major regulated pollutants emitted by a diesel urban bus are nitrogen oxides (${\mathrm{NO}}_x$) and particulate matter (PM). These emissions depend on the engine and its strategies (injection, exhaust-gas recirculation, after-treatment devices, etc.), altitude, weather conditions, route, and driver. This work studies the effect of two fuels, one of them oxygenated, on both ${\mathrm{NO}}_x$ emissions and particle-size distributions in comparison with a diesel fuel used as reference. The study was carried out with buses operating in two different cities, one of them located at around 650 m above sea level and the other near sea level. The test fuels were a binary blend of ethanol and diesel fuel (denoted as ED) and a diesel fuel without biodiesel (denoted as D). Emissions were measured using a Horiba OBS-1300 gas analyzer and a TSI engine exhaust particle sizer spectrometer. Results showed a reduction in both ${\mathrm{NO}}_x$ emissions and total particle number concentrations with altitude, independently of fuel tested, and an increase in geometrical mean diameter. Effective density was used as a particle-diameter-conversion factor to estimate particle mass concentration. However, the negative effect of ED on ${\mathrm{NO}}_x$ emissions and the positive effect on PM were both attenuated by altitude.

This work investigates the effect of n-butanol on combustion processes in a direct injection spark ignition (DISI) engine through the analysis of flame front propagation. Specific attention is given to the sensitivity of n-butanol when changing injection mode in terms of timing and number of injections. Tests were carried out on an optically accessible single-cylinder DISI engine fueled with n-butanol and gasoline, alternatively. The engine is equipped with the head of a commercial turbocharged engine with similar geometrical specifications (bore, stroke, compression ratio). The head has four valves and a centrally located spark device. A conventional elongated hollow piston is used and an optical crown, accommodating a fused-silica window, is screwed onto it. The injector is side mounted and features six holes oriented so that the spray is directed toward the piston crown. During the experimental activity, injection pressure was maintained at 100 bar for all conditions; homogeneous charge conditions performed through single- and split-injection strategy (i.e., two injections per cycle) were compared for investigating their influence on combustion and emissions. Cycle-resolved visualization was applied in order to follow the combustion process, from ignition to the completion of flame front propagation. Macroscopic parameters (inflamed area, shape factor) and microscopic data (curvature distributions) were evaluated through image processing. All the optical data were correlated with conventional measurements of thermodynamic analysis and exhaust emissions. The effect of split injection was found to be relatively negligible for gasoline, while significant differences were recorded when switching from single to double injection for butanol. This points to a different mixture formation process, mainly related to the evaporative properties of butanol.

The work describes an experimental investigation of propane flames established through fuel injection and gradual premixing with preheated and vitiated oxidizing air, within a double-cavity arrangement, formed along a cylinder and two concentric disks. Ignition of the inlet stratified and vitiated mixture and flame stabilization is established at the recirculation region of the afterbody disk. Measurements of mean velocities, temperatures, ${\mathrm{OH}}^{*}$ and ${\mathrm{CH}}^{*}$ chemiluminescence and gas analysis provided information for the interpretation of the relative variations in flame structure and burner performance. The study illustrates some aspects regarding the influence of the preheated/vitiated conditions on the combustion of the inlet stratified fuel-air mixture profile, with respect to flame front stabilization, disposition, and burner emissions. Some important differences in the vitiated flame structure and topology are discussed in comparison to the unvitiated case characteristics, in an initial effort to establish the possible advantages or disadvantages of incorporating preheat and vitiation in stratified operation.

The present investigation compares the combustion, performance, and exhaust emissions of diesel fuel in blends with either 24% $n$-butanol or 24% diethyl ether (DEE), and of vegetable (cottonseed) oil in blends with either 20% $n$-butanol or 20% diethyl ether, fueling a standard, experimental, single-cylinder, four-stroke, high-speed direct injection (HSDI), Hydra diesel engine operated at three different loads. Fuel consumption, and exhaust smoke, nitrogen oxides (NOx), carbon monoxide (CO), and total unburned hydrocarbons (HC) were measured. The differences in combustion, performance, and exhaust emissions of those biofuel blends are compared from the baseline operations, i.e., when working with the neat base fuels (diesel fuel or vegetable oil). Fuel injection, combustion chamber pressure, heat release rate, and temperature diagrams, reveal interesting features of the combustion mechanisms. These results and the differing physical and chemical properties of those biofuels are used to aid the interpretation of the observed engine behavior. Using $n$-butanol or diethyl ether as fuel extenders to either diesel fuel or vegetable oil (base fuels), reductions of smoke and NOx, decrease of CO, and increase of HC emissions are observed, against the corresponding neat base fuel cases.

To address important ash-related issues associated with burning solid biomass fuels for power generation, this paper reviews results of studies performed at the Northeastern University (NU) Combustion and Air Pollution laboratory and elsewhere under well-characterized conditions. It compares the physical and chemical characteristics of fine ash emissions generated from the combustion of pulverized biomasses to those from pulverized coals, since biomass is considered as a substitute fuel for coal in power generation, and assesses their furnace surface deposition propensities. Comparisons show that combustion of some biomasses may generate disproportionally higher emissions of submicron ash particles than combustion of coals (0.03–1.1 versus $0.04–0.06\mathrm{kg}/\mathrm{GJ}$, respectively). The high submicron emissions of biomass are problematic, as conventional particulate control devices have low collection efficiencies for such small particles. Moreover, the chemical composition of submicron particles of biomass typically contain large amounts of alkalis (potassium and sodium), chlorine, sulfur and, often, phosphorous, whereas those collected from combustion of coal contain large amounts of silicon, aluminum, iron, and sulfur. The composition of biomass ashes renders them more amenable to deposition on furnace surfaces, as calculations based on published empirical surface deposition indices show. These calculations, as well as experiences elsewhere, indicate that the slagging and, particularly, the fouling deposition prospects of most biomasses are significantly higher than those of coals.

Low-temperature combustion concepts for transport and power generation employ mixture dilution techniques, such as exhaust gas recirculation (EGR), that offer the potential of fuel flexibility, reduced pollutant emissions, and improved efficiency. These combustion modes, however, display a higher sensitivity to the compositional changes brought about by dilution, which in turn may have an adverse influence on the overall system performance. A fundamental study on the interactions between methane and simulated EGR was carried out on a swirl-stabilized, stoichiometric flame. The effects of varying levels and composition of diluents and preheating temperatures on flame structure and exhaust emissions, were experimentally investigated. Reductions of up to 90% and over 95% in ${\mathrm{NO}}_{\mathrm{x}}$ and CO emissions, respectively, where observed for higher levels of added diluents, whereas an increase in preheating temperature resulted in the opposite trends. It has been further demonstrated that, depending on fuel and the chemical composition of the diluents, chemical effects on ${\mathrm{NO}}_{\mathrm{x}}$ and CO emissions can be very significant.

The purpose of this study is to investigate the effect of the bioethanol port injection ratio and the in-cylinder diesel injection timing on combustion and exhaust emissions characteristics using a dual-fuel combustion strategy. Dual-fuel combustion was applied to a single-cylinder diesel engine with a displacement volume of $373.3{\mathrm{cm}}^3$. In a diesel–bioethanol dual-fuel combustion system, there is no need for additives to solve any phase separation between diesel and bioethanol. The combustion and emissions characteristics were investigated through the study of the indicated mean effective pressure (IMEP), ignition delay, heat release rate, indicated specific nitrogen oxides (${\mathrm{ISNO}}_{\mathrm{x}}$), indicated specific soot (ISsoot), indicated hydrocarbon (ISHC), and indicated carbon monoxide (ISCO). It revealed that IMEP increased with increases to the bioethanol port injection ratio, and the effect of bioethanol on IMEP can be clearly observed in early injection timing. The rate of combustion pressure rise decreased with an increase of port injection ratio. The ignition delay increased with an increase of the bioethanol port injection ratio and with the advance of the in-cylinder injection timing. ${\mathrm{ISNO}}_{\mathrm{x}}$ and ISsoot emissions can be simultaneously reduced by a diesel–bioethanol dual-fuel combustion strategy because of the high latent heat and oxygen content of bioethanol. The ISHC and ISCO emissions in the dual-fuel combustion (DFC) generally increased with the port injection ratio. However, when the in-cylinder injection fuel flowed into the squish region, the ISCO emission decreased with an increase of port injection ratio due to the oxygen effect of bioethanol.

Natural gas (NG) is a gaseous fuel, which has been extensively used and investigated in spark-ignition automotive engines (SI). Combining it with lean combustion has shown the potential to reduce emissions and improve efficiency compared to stoichiometric gasoline engines. The main limitations of lean NG combustion are instability and ignitability. Supplementing NG with hydrogen (H2) is considered a solution to lean NG combustion limitations and it has been studied extensively in the literature. This study is focused on reviewing the work performed by researchers on the effect of partial supplementation of NG by ${\mathrm{H}}_2$ on combustion, emissions and performance of SI automotive engines. ${\mathrm{H}}_2$ addition has been shown to accelerate combustion, extend the lean ignition limit, and improve combustion efficiency. However, it decreases the power output of the engine and increases heat transfer to cylinder walls. The lean ignition limit extension offered by ${\mathrm{H}}_2$ enables increased efficiency and ${\mathrm{NO}}_{\mathrm{x}}$ reduction.

This study examines engine and vehicle performance during the UDDS (urban dynamometer driving schedule) driving cycle of a heavy-duty truck. The most important and novel feature of the analysis is the application of a zero-dimensional model for the simulation of the thermodynamic processes on a crank angle degree basis; a considerable differentiation from the usual mean-value modeling approach of past research is thus accomplished, with the ability to provide insight into the relevant engine processes. The simulation covers the behavior of the whole vehicle (tires, suspension, gearbox, driver, etc.) during the cycle, focusing on the prominent engine emissions (soot, ${\mathrm{NO}}_{\mathrm{x}}$, and ${\mathrm{CO}}_2$) at each acceleration event. Road-type, tire-type, and vehicle-size effects are also taken into account through a relevant parametric study.

Engine start is a critical process of diesel engine operation with respect to the stability of the combustion process, specific fuel consumption, and pollutant emissions among others. Additionally, the starting is a transient process included into the New European Driving Cycle (NEDC) established for the certification of light-duty vehicles. In this work, a turbocharged, direct injection (DI), diesel engine equipped with a common rail injection system and an exhaust gas recirculation (EGR) strategy has been tested during the starting. The engine was tested at two different starting modes: NEDC cold start mode (temperature of cooling water and lube oil were approximately ambient temperature $\sim 20°\mathrm{C}$) and warm start (the engine was previously warmed up). Regulated pollutant emissions and operating parameters such as engine speed, air and fuel mass flow rates, EGR valve position, etc. were registered during the tests. The engine was fueled with a low sulfur fossil diesel fuel and with three different biodiesel fuels derived from rapeseed, sunflower, and soybean oils. Biodiesel fuels were tested pure and blended with fossil diesel fuel. Results showed that biodiesel fuels led to a reduction of smoke opacity, hydrocarbons, and carbon monoxide during both NEDC cold and warm engine start with similar nitrogen oxide emissions. This work demonstrates that emissions from engine start strongly depend on the injection and exhaust gas recirculation control strategies.

The effect of electrostatic fields on the dilute plasma of chemi-ions generated by a non-premixed, $N_2$-diluted, methane-oxygen flame was studied in an experimental burner whereby a counterflow flame was positioned between the parallel plates of a large-scale capacitor. It was shown that flame morphology and location could be controlled solely through electrostatics. The location of the flame could be controlled through applied voltage, virtually independently of overall mixture composition and strain rate applied on the flame. In fact, through electrostatic actuation, it was possible to push the flame without extinction literally at the fuel nozzle, where there is very little oxidizer. Also, a computational framework for the study of these flames was developed in a computer program and verified with previous computations of the same flame. In future work, this framework will be used in tandem with the electrostatics computations that the computer program enables in order to probe the underlying physics of the flame.

Homogeneous charge compression ignition (HCCI) combustion encompasses the advantages of both diesel and gasoline fuel engines. However, shortcomings mainly associated with the rapid pressure rise rate need to be studied in detail and account for the inherencies of each fuel mixture. The work numerically investigates the effect of key operating parameters on performance and pollutant characteristics on a widely investigated research engine. An accredited, detailed chemical kinetic mechanism for gasoline surrogate components, coupled with a ${\mathrm{NO}}_{\mathrm{x}}$ sub-mechanism, is implemented on a commercial 0D single-zone engine model, in order to identify optimum performance guidelines regarding operating parameters using typical primary reference fuels. The effect of operated fuels, intake charge and exhaust gas recirculation (EGR) levels are discussed based on pressure traces, heat release rate profiles, combustion phasing analyses, and in-cylinder speciation and kinetic information. The work also explores the applicability and limitations of such an approach and investigates the extent to which a solid methodological approach based on detailed kinetic models could be helpful for gaining some chemical insight on the heat release and pollutant formation processes.

Various solutions have been proposed for reducing the exhaust emissions and improve the well-known soot and nitrogen oxide (NO) trade-off in diesel engines, without making serious modifications to the engine, one of which is the use of natural gas as supplement to liquid diesel fuel. In these types of engines, referred to as fumigated, natural gas–diesel dual-fuel compression ignition (CI) engines, gaseous fuel is fumigated and premixed with the aspirated air during the induction stroke. Natural gas is a clean-burning fuel with a relatively high auto-ignition temperature, which is a serious advantage in dual-fuel combustion. Previous research studies have shown that the natural gas–diesel fuel dual-fuel combustion in a CI engine environment, compared with conventional diesel fuel operation, suffers from high specific fuel consumption and high carbon monoxide (CO) and unburned hydrocarbon (HC) emissions. Compression ratio (CR) and diesel fuel injection timing (IT) are two engine parameters that can influence considerably the combustion process inside the combustion chamber of a dual-fuel CI engine. For examining the effect of these parameters on the performance and exhaust emissions of a light-duty diesel engine fueled with methane, which is the basic constituent of natural gas, a theoretical investigation is conducted in this work by using a numerical simulation. The results concern engine performance characteristics, NO, CO, and soot emissions for various methane-diesel mass ratios at engine partial-load conditions and constant speed, by using a comprehensive two-zone phenomenological model. Model predictions were tested and validated against experimental measurements obtained from a fumigated methane–diesel dual-fuel CI engine, operating with constant CR and constant diesel fuel IT under constant engine speed and partial-load conditions for various methane-diesel fuel mass ratios. The main objective of the comparative assessment shown in this work is to record and comparatively evaluate the relative impact of CR and diesel fuel IT on the engine performance characteristics and emitted pollutants. The conclusions from the present investigation may be very valuable for the use of natural gas as a supplementary fuel in conventional dual-fuel engines. From the comparative evaluation of the theoretical findings presented in this work, it is generally revealed that for a turbocharged dual-fuel (i.e., methane–diesel) CI engine, operating at partial-loading conditions and high gaseous fuel mass ratios, the increase of CR (accompanied with advanced diesel fuel IT) could be a promising solution for improving engine power output and efficiency while simultaneously reducing CO emissions. Conversely, at lower gaseous fuel mass ratios, the simultaneous increase of both parameters could cause problems to the engine structure because the maximum cylinder pressure becomes considerably higher compared with that observed under normal engine operating (NEO) mode, which may prove to be harmful for the engine’s structural integrity.

This work simulates the Megalopolis IV power plant boiler operation in terms of NOx emissions for a wide range of thermal loads, and with different operational patterns of the firing system, i.e., different numbers and variation of the open burners’ positions. This work provides feedback on thermal loads that are lower than the current technical minimum ($\sim 55\%$) using numerical tools (CFD software packages) for both 40 and 35% partial-loads. For the lowest investigated load, it also examines contemporary combusting systems, with the simultaneous firing of raw and stored dry lignite to achieve flame stability. The results of the current study primarily focus on the effect of lower than 100% boiler operation on the NOx emissions because the majority of works in literature investigates boiler NOx emissions only under full-load conditions. Furthermore, it focuses on the variation of the NOx emissions among different partial-load conditions and the influence of the firing system operational patterns on these. To reduce the required computational resources, the decoupled approach is adopted, which distinguishes the main combustion mechanisms from the NOx emission mechanisms themselves. The results indicate that the NOx emissions concentration reduced at 6% dry oxygen molar concentration at the main furnace outlet surface increases as the thermal load gets lower. The results also prove the direct relation between temperature values and NOx emissions because the highest NOx concentrations are tracked in the hot spot areas; primarily attributed to thermal NOx production mechanisms. Additionally, the firing system operational pattern for each specific thermal load affects the NOx emissions concentration, as the results regarding the 35% partial-load case imply. In particular, for the 35% partial-load case, the even distribution and injection of stored dry lignite from all six vapor burners result in lower NOx concentrations compared to the case for which the injection of the stored dry lignite happens through the inlets of the two open vapor burners. In conclusion, the results of this work can provide valuable information about the boiler performance in terms of its NOx emissions behavior under partial-load conditions, and provide potential measures that can be implemented for NOx emissions reduction, especially under low-thermal conditions.

Thermal desalination systems consist of phase-change operations to separate freshwater from bulk seawater. Solar desalination systems involve partial vaporization of seawater, known as flashing, using solar heat then condensation of flashed steam to produce fresh water. The latent heat of the condensing steam is usually utilized to preheat seawater, thus increasing the energy efficiency of the desalination systems. Evaluating the feasibility of a solar desalination system requires accurate determination of seawater preheat temperature exiting the condenser to enter the evaporator. Determining this temperature is very challenging due to the complicated phase-change dynamics and the existence of noncondensable gases in the condenser that were dissolved in seawater. The preheat temperature depends on several factors such as seawater flow rate, system vacuum, and flashed vapor temperature. This study utilizes the kernel ridge regression (KRR) method to predict the preheat temperature as a function of these factors. KRR is an efficient algorithm that utilizes kernel methods to model highly nonlinear relations. The results show the prediction of preheat temperature is highly accurate and it outperforms the state-of the-art regression model of support vector machines in terms of efficiency.

Coal is a very important fuel for power generation because of its abundant reserves, stable prices, and widely distributed countries of origin. However, coal firing emits carbon dioxide more than other fuels do, which is not desirable from the standpoint of preventing global warming. The only practical and economical solution to this dilemma is to raise plant efficiency. For over a century, power plants have been on the basis of the Rankine cycle. Currently, a combined cycle is commercially utilized and plant efficiency has greatly improved. A natural gas combined cycle is now almost a standard. Then why is it not applicable for coal? A coal-fired combined cycle, the so-called integrated coal gasification combined cycle (IGCC), has long been desired and several large-scale units are in operation. This paper will discuss the current situation of IGCC technology, reflecting on the lessons learned from past IGCC projects and reviewing key points for successful commercialization of IGCC on the basis of experiences with IGCC in Japan, and will provide a suggestion that is applicable worldwide.

Emission reduction from marine engines can be supported by implementing multiple injection strategies. In the present study, the effect of fuel post-injection on the performance and exhaust emissions of a large two-stroke marine diesel engine is investigated by using computational fluid dynamics (CFD). An optimization procedure is formulated by coupling a KIVA-3-based CFD code with an optimization tool based on evolutionary algorithms (EAs). A fuel-injection profile consisting of two pulses (main and post-injection) is considered and parameterized in terms of four design variables. The specific fuel oil consumption (SFOC) and the final concentration of nitric oxides (${\mathrm{NO}}_{\mathrm{X}}$) and soot constitute the objective functions. Using a parametric study, two multiobjective optimization problems are formulated, an unconstrained and a constrained one; in the latter, the work output per engine cycle and the maximum in-cylinder pressure are the problem constraints. For both problems, significant reductions in pollutant emissions are attained, in comparison with a reference case characterized by continuous injection; for the constrained problem, the reductions reach 23 and 32% for ${\mathrm{NO}}_{\mathrm{X}}$ and soot, respectively.

Stirling engines, as external combustion engines, can be powered using a variety of heat sources achieving significantly reduced emissions. Energy systems using Stirling engines optimize their performance in specific operating conditions. Their capacity depends on the geometric characteristics of the machine, the design of the unit, and the environment in which it works, as well as the size of the load. Therefore, the numerical analysis of each Stirling engine using more realistic independent variables is crucial for predicting the actual indicated power and efficiency for a given engine speed, mean pressure, and heater and cooler metal temperatures. A comprehensive thermodynamic analysis of the Solo 161 V Stirling engine, using the Stirling engine thermodynamic analysis model (SETAM) is presented. Working gas friction pressure drop is presented all over the engine, but mostly in the regenerator. The gas mass flow is laminar in the regenerator and turbulent at the heater and cooler. The regenerator porosity and matrix wire diameter are critical to the Stirling engine performance. The steady state condition of the engine depends on the regenerator matrix heat capacity. High matrix porosity values leads to high regenerator effectiveness but to low engine performance. An increase of the matrix heat capacity leads to reduction of the engine’s performance, the torque as well as the work output. A low speed engine is more effective with a low porosity regenerator installed. Engine performance can be independent by the speed at specific matrix porosity value. The temperature profile of the working medium in the regenerator is presented in relation to position and time. The nonideal behavior of the regenerator is demonstrated and the remaining heat in the regenerator grid is recorded when the thermal equilibrium is achieved. The effect of the regenerator’s geometrical characteristics on its effectiveness and on engine’s performance is recorded. An optimal construction design area for the regenerator, leading both to high engine’s efficiency and performance levels in certain operating conditions is presented. The Stirling engine performance in various operating conditions in relation to its geometrical characteristics is investigated.