Conventional Hydrocarbon Fuels Research Articles

Experimental investigation on accelerated generation of HHO gas using titanium electrodes with platinum and mixed metal oxide coating - A comparative study

HHO gas is an alternate source of fuel that can be used in automobiles as a clean fuel with reduced carbon emissions, replacing the conventional hydrocarbon fuels being used today. Many different methods are involved in the production of this gas. Among these methods, alkaline water electrolysis is one of the easiest and most reliable methods for production. Though there are many limitations in the storage of Hydrogen, the HHO gas has been produced on-site using alkaline water electrolysis. This article mainly focuses on the production of HHO gas for different operating parameters and conditions, such as change of electrolyte, electrode material coating, effect of temperature and the surface area of the electrode. The electrolytes used in the electrolyser are sodium hydroxide (NaOH) and potassium hydroxide (KOH). The electrode material is titanium coated with two different materials namely Mixed Metal Oxide (MMO) and Platinum (Pt) respectively. A maximum yield of 0.9 LPM of HHO gas has been generated when supplying 40 amps of current to the electrolyser unit coated with MMO and KOH as electrolyte. Use of KOH electrolyte results in higher production rate when compared to NaOH. MMO coated titanium electrode produces more HHO gas when compared to platinum coated electrode.

Effects of ammonia addition on the soot nanostructure and oxidation reactivity in n-heptane/toluene diffusion flames

Co-firing NH3 with conventional hydrocarbon fuels is an important approach for reducing CO2 emissions in existing combustion systems. Besides CO2, the blending of NH3 would also notably affect soot formation and its oxidation behaviors. In the present study, we focus on the effects of NH3 on the nanostructure and oxidation characteristics of soot produced in diffusion flames of n-heptane/toluene mixtures. Two configurations of laminar co-flow diffusion flame, including both normal and inverse diffusion flames (NDF and IDFs), were used for investigation. High-resolution transmission electron microscopy (HRTEM), Raman spectroscopy (Raman), and Thermogravimetric analysis (TGA) were employed for soot characterization. The HRTEM and Raman spectra showed that with the increase of NH3 blending ratio, the fringe length (La) and the degree of graphitization decreased while the microcrystal tortuosity (Tf) increased. The results are in consistent with TGA analysis which suggests the promoting effects of NH3 on the soot oxidation reactivity. Difference between NDF and IDF with respect to the soot nanostructure and oxidation activity were discussed. It is our hope that the present results could deepen our understanding on the effects of NH3 on soot nanostructure and oxidation behavior and benefit the design of particulate filters for combustion devices fueled with hydrocarbon/NH3 mixtures.

Combustion Behavior of Fuel Droplets with Metallic, Non-Metallic and Organo-Metallic Boron Additives

ABSTRACT There is considerable interest in the utilization of fuels derived from boron materials, with their high calorific value, in various applications ranging from propellants to pyrotechnics. Conversely, their impact on the combustion behavior of conventional hydrocarbon fuels remains largely unclear. In this study, ignition, combustion, micro-explosion and simultaneous atomization behaviors of gasoline-based alternative fuels containing metallic (28–35 µm MgB2), nonmetallic (1 µm amorphous boron, 10 µm AlB12 with 86–88% and 95–97% purity) and organo-metallic boron derivatives (triethyl borate (TEB) containing C2H5 groups and trimethyl borate (TMB) containing CH3 groups) were investigated. The experiments were carried out at droplet scale and recorded using a high-speed camera and a thermal camera. The findings revealed a systematic reduction in ignition delay for each gasoline fuel enriched with boron derivatives. 2.5%AlB12/G and pure TMB droplets were the fastest extincting fuel droplets (0.9678 s and 1.245 s, respectively). The highest maximum flame temperature was recorded as 626 K and 610 K for pure TMB and 80%TEB/G, respectively. Droplet diameter regression analyses showed that the diameters of fuel droplets containing predominantly metallic and nonmetallic boron derivatives decreased in accordance with the d 2 -law. This study demonstrated that cost-effective and easily producible amorphous boron and organometallic boron derivatives are promising energy carriers for hydrocarbon fuels.

Ultra-slow ammonia flame speeds — A microgravity study on radiation

Ammonia/air flames burn slowly and are consequently affected by buoyancy-, radiation-, and stretch-related uncertainties more than many conventional hydrocarbon fuels. In this work, unique buoyancy-free ammonia/air flame speed data were acquired and analyzed, specifically considering the impact of radiation. First, outwardly propagating ammonia/air flames near the propagation limits were accurately measured under microgravity using two simultaneous techniques. Flame radius evolution was captured by a high-speed Schlieren arrangement (optical method) in a near-isobaric regime. Accompanying, pressure rise was measured and subsequently used for flame speed extraction during near-isentropic gas compression. A profound nonlinear dependence of flame propagation speed on stretch was captured over the optical results in the observable range of the current setup, which illustrates the limitations of the optical method in comparison to the pressure-rise method. Radiation-corrected optical and pressure-rise results have shown good agreement along multiple isentropes, thereby cross-validating applied methodologies and highlighting very good consistency of the acquired data. Pressure-rise data analysis has shown sensitivity in the assessment of kinetic mechanisms to the radiation effect. In the absence of appropriate radiation correction for flame speed data, misinterpretations may arise regarding the accuracy of kinetic models, introducing challenges in the development of accurate kinetic models. The performance of the chemical kinetic models was quantified in a wide range of unburned gas temperatures (< 500K) and pressures (< 9.3bar) against distinctive experimental flame speed data with and without radiation correction acquired under microgravity indicating good performance of the Han et al. (2019) model.

Numerical Prediction on In-Cylinder Mixture Formation and Combustion Characteristics for SIDI Engine Fueled with Hydrogen: Effect of Injection Angle and Equivalence Ratio

Although their ease of transport, storage, and use makes hydrocarbon fuels dominant in commercial energy systems, the emission of harmful gases, including greenhouse gases, is a fatal disadvantage. Despite ongoing research to improve thermal efficiency and reduce the emissions of internal combustion engines using conventional hydrocarbon fuels, achieving net-zero carbon requires decarbonizing fuels rather than reducing the use of internal combustion engines. Hence, transitioning away from hydrocarbon fuels and evolving internal combustion engines into clean engines using carbon-free fuels, such as hydrogen, is necessary. This study designs a 2.0 L research engine and numerically analyzes its combustion characteristics and spray behavior by varying the spray angle and equivalence ratio. When comparing the turbulence kinetic energy at a 45-degree spray angle with that at 30 degrees and 60 degrees, on average, there was a difference of approximately 37.54 m2/s2 and 26.21 m2/s2, respectively. However, misfires occur in the lean condition. Although hydrogen has a wide flammability range, poor mixture formation under lean conditions can result in misfires. The 60-degree spray angle resulted in the highest combustion temperatures and pressures for all equivalence ratio conditions, consequently leading to the highest emissions of nitrogen oxides. Specifically, at a lambda value of 2.5, the 60-degree spray angle emitted approximately 29 ppm, 0 ppm, and 161 ppm of nitrogen oxides for each respective spray angle.

The methodology of decoupling fuel and thermal nitrogen oxides in multi-dimensional computational fluid dynamics combustion simulation of ammonia-hydrogen spark ignition engines

Under the paradigm of carbon neutrality, ammonia-hydrogen (NH3–H2) blended fuel presents itself as a zero-carbon alternative to petroleum-based fuels, effectively reducing carbon emissions originating from internal combustion engines. In the combustion process of conventional hydrocarbon fuels, the production of nitrogen oxides (NOX) predominantly arises from nitrogen present in the atmosphere, which occurs through the Zeldovich mechanism under high-temperature conditions. These NOX species, commonly referred to as thermal NOX, rely on inert nitrogen. However, the utilization of ammonia fuel activates the reactivity of nitrogen element, leading to the nitrogen-containing species formation, including NOX, termed as fuel NOX. Consequently, the combustion of ammonia-hydrogen fuel entails the coupling of thermally formed nitrogen oxides and fuel-derived nitrogen oxides. The generation of NOX is significantly influenced by the physicochemical environment, while the transient combustion conditions within the engine combustion chamber further complicate the process of NH3–H2 combustion and NOX formation. As a consequence, comprehensively investigating the NOX emission characteristics in NH3–H2 engines presents a considerable challenge. By decoupling fuel NOX and thermal NOX, a more profound understanding of NOX emission control strategies for ammonia-hydrogen engines can be attained. This research paper accomplishes the decoupling of fuel nitrogen elements and atmospheric nitrogen elements in three dimensional computational fluid dynamics engine combustion simulations. The results indicate that this decoupling methodology disregards the differentiation between the fuel NOX pool and the thermal NOX pool, resulting in a slight modification in NOX concentration. Nevertheless, this approach has minimal impact on the combustion process, ensuring that the NOX formation environment remains largely unchanged. Furthermore, it successfully demonstrates the spatial and temporal distribution characteristics of thermal NOX and fuel NOX, thereby furnishing an effective analytical tool for the comprehensive study of NOX emission characteristics in NH3–H2 engines.

Potential of ethanol and butanol in reducing deposits of DISI engine injectors

The operation of conventional (hydrocarbon) fuels causes certain effects in the internal combustion engine. Despite the satisfactory efficiency of internal combustion engines, their fuel systems, particularly the injectors, are subject to constant fouling. The article analyzes the possibility of reducing the deposit of high-pressure gasoline injectors using the alcohol addition of ethanol and butanol. The study was conducted under the engine and non-engine conditions. Fuel injection timing was analyzed when fueling with different mixtures, and non-engine analyses were conducted to determine changes affecting the injectors. The results indicate the possibility of reducing injector hole coking using ethanol and butanol as a 20% additive to the base fuel.

Recalibration of carbon-free NH3/H2 fuel blend process: Qatar's roadmap for blue ammonia

Due to growing concerns about carbon emissions, using zero-carbon fuels has become an interesting alternative to overcome this problem. The NH3(70%)-H2(30%) fuel blend is an innovative fuel example that has the potential to replace conventional hydrocarbon fuels. Studies on the NH3(70%)-H2(30%) fuel blend have shown its superior combustion performance and its effect on enhancing cycle efficiency compared to other compositions of the NH3–H2 blends. However, without calibrating ammonia plants and simply mixing portions of the produced pure ammonia to hydrogen at the desired molar fraction essentially requires coupling ammonia plants with other hydrogen-producing plants, leading to potential difficulties in commercializing the unused (as fuel in the NH3–H2/air gas turbines) hydrogen portions from the hydrogen-producing plan. Therefore, in this paper, as an attempt to utilize the existing ammonia production infrastructure and facility without acquiring major changes that could lead to resisting the adoption of the NH3(70%)-H2(30%) fuel blend, the independent parameters of a conventional ammonia plant have been calibrated, and the reactors have been sized to provide a continuous supply of the NH3(70%)-H2(30%) fuel blend with the exact molar fraction to run a power plant. Calibrating of the ammonia plant has been performed using an ASPEN PLUS model.

Sorghum-Based Power Generation in Southern Ukraine: Energy and Environmental Assessment

An increase in energy demand, fossil fuel reserves depletion, and environmental issues are primary reasons for renewable energy use, including power generation. Bioenergy is the primary alternative to conventional hydrocarbon fuels. Biomass-based power generation is increasing due to some reasons, including a gradual decrease in the levelized cost of electricity and a reduction of carbon dioxide emissions. Sorghum is a promising energy crop for semi-arid climate zones, including southern Ukraine. It can be used for both biofuel production and power generation. However, there is a lack of methodology for energy and environmental assessments of sorghum-based power generation. Some possible technologies were analyzed. The novelty of this study is the accounting of energy consumed and carbon dioxide emissions during crop cultivation. We have determined that sorghum-based power plants can generate from 2 to 12 MWh per hectare. Their operation significantly reduces carbon dioxide emissions (from 613 to 3652 kg of carbon dioxide per hectare of sorghum silage cultivation). Sorghum-based biogas plants have energy and environmental advantages if they use co-generation technologies and utilize digestate as a biofertilizer. The utilization of digestate (obtained from silage production per hectare) substitutes up to 12.8 MWh of indirect energy. The results obtained can be used by farmers and authorities for bioenergy development.

Combustion and performance characteristics of SI engine with bioethanol blended fuels

The combustion characteristics of single-cylinder spark-ignition (SI) engines with bioethanol blended fuels have been investigated experimentally. It is known that bioethanol (alcohol-based fuel) offers a range of advantages to be considered as a fuel for SI engines. This advantage range from its renewability to comparable fuel properties to conventional hydrocarbon fuels. Moreover, bioethanol can be produced from agricultural and municipal waste. The environmental benefits of bioethanol include its low contamination of atmosphere and reducing the dependency on conventional (eg, gasoline) fuel for the automotive sector. Analyses have been carried out to show the influence of bioethanol blended fuels (from 10% by vol. to 80% by vol.) on combustion and engine performance characteristics. Furthermore, the investigation is carried out for different blends and across different engine speeds including cycle-to-cycle variation analysis. Here pure gasoline (which already contains 10% by vol. ethanol) has been taken as a reference case. The apparent heat release rate has been computed using in-cylinder pressure. There is a significant increase in heat combustion with the increase in bioethanol contained in the fuel and maximum heat combustion is observed with a 60% bioethanol blend at higher engine speed. The fuel consumption increases with the increase in bioethanol percentage when compared with the reference case. Bioethanol addition to gasoline increases the in-cylinder peak pressure during combustion and overall volumetric efficiency. The results suggest that the E20 case shows a favorable choice and can be used over the E10 case for the studied engine without making any adjustments to the engine parameters (or engine control unit).

Numerical investigation of a first-stage stator turbine blade subjected to NH3–H2/air combustion flue gases

Blending ammonia with hydrogen has the potential to replace conventional hydrocarbon fuels of jet engines and gas turbines to reduce carbon emissions. Previous research on the 70% NH3–30% H2 (vol%) fuel blend characterized its cycle efficiency and emissions, however, the thermal and aerodynamic effects of the NH3–H2/air combustion flue gases on the turbine blades were not identified. Therefore, the novelty of the analysis presented herein appears in characterizing such effects of the NH3–H2/air combustion flue gases on a generic turbine blade model using CFD simulation for lean (Φ = 0.75), stoichiometric (Φ = 1.00), and rich (Φ = 1.25) equivalence ratios, which are compared to a CH4/air combustion flue at Φ = 0.75, 1.00 and 1.25, respectively. Based on the obtained results, a cooling channel's ability to reduce the blade's temperature was negligible based on the temperature difference between the leading edge of the turbine blade and the temperature of the combustion flue gas at the inlet. As the combustion equivalence ratio was increased from 0.75 to 1.25, a second shockwave forms at the leading-edge surface, projecting across the blade's lower edge. The formation of the second shockwave was found to be increasingly significant for the NH3–H2/air mixture on the downstream flow when compared to a CH4/air flue gas. Furthermore, increasing the NH3–H2/air equivalence ratio improved the blade's ability to increase the average overall outlet Mach number compared to the inlet flow. Flow separation near the trailing edge remained relatively unaffected with increasing equivalence ratio. However, separation near the leading edge at the blade's lower edge becomes more significant for the NH3–H2/air combustion flue gases compared to CH4/air combustion, causing a large circulation zone under the blade's lower surface due to the higher kinematic viscosity for the NH3–H2 fuel to the CH4 fuel (i.e., 2.06 ×10−5cm2/s and 1.75 ×10−5 m2/s, respectively). The circulation induces a higher viscous force and fluid inertia in the boundary layer, causing higher levels of separation. Turbulence intensity was also found to be significantly increased for the NH3–H2/air flow to that of the CH4/air combustion flue gases with increasing equivalence ratio.

Property-based quantitative risk assessment of hydrogen, ammonia, methane, and propane considering explosion, combustion, toxicity, and environmental impacts

In this study, a quantitative risk assessment of decarbonized new fuels, such as hydrogen and ammonia, and conventional hydrocarbon fuels, such as methane and propane, is conducted. The assessment focuses on the aspects of explosion, combustion, toxicity and environment to find answers for the questions “Which fuel is more dangerous?” and “How much?”. To assess the risk of each fuel, not for specific applications, but for general purposes, risk related fuel properties are used to calculate the risk intensity and risk frequency. Considering the risk frequency, the degree of risk is calculated as hydrogen > propane > methane > ammonia. In terms of the risk intensity, the degree of risk is changed as propane > methane > hydrogen > ammonia. The total risk score, which is a multiple of the risk frequency and intensity, is derived as propane (47.6 pts) > methane (31.5 pts) > hydrogen (31.2 pts) > ammonia (15.4 pts). Hydrogen shows high risks in the flammability limit, minimum ignition energy, adiabatic flame temperature and laminar burning velocity while ammonia shows high risks in toxicity. The results obtained from the risk assessment are expected to reinforce the weak points of decarbonized alternative fuels for their safe use in energy conversion systems.

High Load Compression Ignition of Wet Ethanol Using a Triple Injection Strategy

Wet ethanol is a biofuel that can be rapidly integrated into the existing transportation sector infrastructure and have an immediate impact on decarbonization. Compared to conventional hydrocarbon fuels, wet ethanol has unique fuel properties (e.g., short carbon chain, oxygenated, high heat of vaporization, no cool-flame reactivity), which can actually improve the efficiency and engine-out emissions of internal combustion engines while decarbonizing. In this work, wet ethanol 80 (80% ethanol, 20% water by mass) was experimentally studied at high loads under boosted conditions in compression ignition to study the tradeoffs in efficiency and emissions based on boosting and injection strategies. Specifically, this work explores the potential of adding a third, mixing-controlled injection at high loads. The results indicate that adding a third, mixing-controlled injection results in combustion stabilization at high loads, where the peak pressure limit of the engine is a constraint that requires combustion phasing to retard. However, since the heat of vaporization of wet ethanol 80 is ~6% of its lower heating value, evaporation of fuel injected near top dead center imposes a thermodynamic efficiency penalty by absorbing heat from the working fluid at a time in the cycle when adding heat produces net work out. Additionally, the mixing-controlled injection increases NOx emissions. Therefore, the amount of fuel injected in the mixing-controlled injection should be limited to only what is necessary to stabilize combustion. Ultimately, by using wet ethanol 80 in a triple injection strategy, a load of 22 bar IMEPn is achieved with a net fuel conversion efficiency of 42.2%, an engine-out indicated specific emissions of NOx of 1.3 g/kWh, and no measurable particulate matter, while maintaining a peak cylinder pressure below 150 bar.

Flamelet modeling of forced ignition and flame propagation in hydrogen-air mixtures

Modeling hydrogen-air flames is challenging for several reasons. Due to its high diffusivity and reactivity, the combustion properties of hydrogen are substantially different from conventional hydrocarbon fuels. Besides differential diffusion and flame stretch, which play an important role in hydrogen combustion, the prediction of ignition events is also relevant for the safety and control of combustors operating with hydrogen. To address these effects with a manifold-based method, a novel flamelet progress variable (FPV) model is presented which consists of a tabulated manifold and a coupling strategy. In contrast to prior work, the manifold is coupled to the CFD simulation by transporting major species and enthalpy instead of transporting the flamelet control variables only. A closure approach is developed to employ a mixture-averaged diffusion model accounting for exact diffusion coefficients. Furthermore, a novel tabulation strategy is presented which is based on a recently published composition space model (CSM). The CSM is used for computing and tabulating flamelets which are consistently blended with constant-pressure homogeneous ignition solutions at elevated temperatures. The FPV model is validated for planar and curved hydrogen-air premixed flames across a range of equivalence ratios (0.7≤ϕ≤1.4). The latter are ignited by an energy deposition followed by an outward propagation as cylindrical or spherical expanding flames. It is shown that the FPV model accurately recovers the characteristics of the forced ignition process in both quiescent mixtures and a counterflow configuration, as well as the flame structures and propagation speed of the outwardly propagating hydrogen-air flames.

Combustion and emission characteristics of a compression ignition engine burning a wide range of conventional hydrocarbon and alternative fuels

General aviation aircraft driven by aviation piston engines (APE) have gained a broad range of applications. Aviation fuels blended with long-chain alcohols is a promising means for APE to mitigate its dependency on fossil fuel. Herein, the combustion and emission characteristics of an aviation compression ignition engine burning a baseline diesel, the RP-3 kerosene, and a synthetic Fischer-Tropsch (FT) fuel were analyzed. The engine tests were carried out under different conditions via varying pentanol additive ratio (PAR), fuel injection timing and engine load variables. The Response Surface Method (RSM) was utilized to quantify the effectiveness of independent variables on the target responses of indicated thermal efficiency (ITE), nitrogen oxides (NOx) and particulate matter (PM) emissions. Compared to the baseline diesel, burning the pentanol-FT blends (40% PAR) significantly reduces NOx by 81% and PM by 75% with a prominent increase of ITE by 7.2%. Based on the analysis of variance, the RSM-derived model demonstrated that the fuel type predominantly determines ITE and NOx, while PAR primarily alters PM emissions. The binary effects of independent variables on the target responses were further resolved quantitatively. Moreover, the RSM was well validated to implement effective prediction on the engine performance/emission characteristics.

Ammonia-hydrogen-air gas turbine cycle and control analyses

Blending ammonia with hydrogen has the potential of replacing conventional hydrocarbon fuels to reduce carbon emissions. However, the uncertainties of determining safe, stable, and efficient operating conditions remain a great challenge. Furthermore, although control technologies have been in the scope of interest for gas turbine manufacturers, those are not yet specialized for NH 3 –H 2 /air gas turbines. Therefore, this paper identifies the cycle performance of an NH 3 –H 2 /air gas turbine in comparison to a CH 4 /air gas turbine, thus highlighting the operating conditions in which the NH 3 –H 2 /air gas turbines show higher performance compared to the CH 4 /air gas turbines. The results have been obtained by developing a LabVIEW code which has also been utilized to serve as a control code for the NH 3 –H 2 /air and CH 4 /air gas turbines. The system identification stage of calibrating the controller has been achieved for both gas turbines by determining the system's sensitivities, thus providing an accurate calibration of the controlling parameters. • Higher NH3–H2/air gas turbines performance compared to CH4/air gas turbines. • System identification, cycle, and sensitivity analyses of NH3–H2/air gas turbines. • Developing and calibrating an NH3–H2/air gas turbines controller.

Analysis of Gas-Turbine Type GT-009 M Low-Toxic Combustion Chamber with Impact Cooling of the Burner Pipe Based on Combustion of Preliminarily Prepared Depleted Air–Fuel Mixture

This article analyzes the mechanism of formation of the main components of harmful emissions characteristic of combustion chambers operating on conventional hydrocarbon fuels. The method of combustion of a preliminarily prepared depleted air–fuel mixture was chosen as the object of the study. This method of suppressing harmful emissions was implemented in the design of a low-toxic combustion chamber developed as applied to the GT-009 M type unit with impact cooling of the burner pipe and provides for stabilization of the main kinetic flame by means of a diffusion-kinetic and a standby burner device. The results of the calculations performed with regard to the operating conditions of the low-toxic combustion chamber at the nominal load of GT-009 M allow us to conclude that the practical use of combustion of a depleted, preprepared, fuel–air mixture in combination with diffusion-kinetic stabilization of combustion is promising. The topic of this article is related to the problem of ecological improvement of gas turbine unit combustion chambers, which determines its utmost importance and relevance.

A Review on Combustion Characteristics of Ammonia as a Carbon-Free Fuel

A comprehensive review of combustion characteristics of ammonia (NH3) as a carbon free fuel is presented. NH3 is an attractive alternative fuel candidate to reduce the consumption of fossil fuel and the emission of CO2, soot, and hydrocarbon pollutants, due to its comparable combustion properties, productivities from renewable sources, and storage and transportation by current commercial infrastructure. However, the combustion properties of NH3 are quite different from conventional hydrocarbon fuels, which highlight the specific difficulties during the application of NH3. Therefore, this paper presents comparative experimental and numerical studies of the application of NH3 as a fuel during combustion process, including the combustion properties of laminar burning velocity, flame structures, pollutant emissions for the application of NH3 as a carbon free fuel. This paper presents the burning velocity and pollutant emissions of NH3 alone and mixtures with other fuels to improve the combustion properties. The aim of this paper is to review and describe the suitability of NH3 as a fuel, including the combustion and emission characteristics of NH3 during its combustion process.

Study of effects of ammonia addition on soot formation characteristics in n-heptane co-flow laminar diffusion flames

Ammonia is a compelling carbon-free fuel, and co-firing ammonia with conventional hydrocarbon fuels receives growing interest as a feasible solution to mitigate CO2 emission. This study experimentally and numerically investigated the soot formation characteristics of n-heptane co-flow laminar diffusion flames with different contents of ammonia (up to 40% by volume, balanced using argon). The soot volume fraction (SVF) in the flames was quantitatively measured via laser-induced incandescence technique; PAHs and OH radical were qualitatively determined via laser-induced fluorescence technique. Results showed that ammonia addition reduced the SVF, i.e., a peak SVF decrease of 35% at 40% ammonia. Meanwhile, PAH content also decreased with ammonia addition, demonstrating that ammonia would effectively inhibit the formation of PAHs. Thus, the inception and growth of soot decreased. Interestingly, OH radical was reduced with ammonia addition, revealing that ammonia also chemically inhibited soot oxidation. The results confirmed that ammonia reduced the soot loading in the flames due to inhibitory effect on the inception and growth of soot rather than the enhancement on oxidation. The established mechanism effectively captured the variation of different PAHs in the experiments. Numerical analysis showed that the formation of the first aromatic ring benzene was reduced by ammonia as a result of the reduction of C4H5 and R203:C4H5+C2H2 reaction. In addition, the reduced hydrogen abstraction due to decrease in H, coupled with the reduced small PAH, led to the decrease in PAH growth. Nevertheless, a more comprehensive mechanism including the reactions between aromatics and nitrogen species, such as NH, CN, and NOx, is still required in future studies.

Multi-Objective Optimization of a RCCI Engine Fueled with Diesel Fuel and Natural Gas Enriched with Hydrogen

The present study seeks to conduct the optimization of a heavy-duty diesel engine under RCCI combustion fueled with diesel fuel and natural gas enriched with hydrogen. Since NOx emission is one of the most important concerns of using hydrogen as a sole fuel or an additive to hydrocarbon fuels in an internal combustion engine like RCCI engine, thus, the main goals of this study are to overcome the NOx challenge, enhance the RCCI combustion characteristics, and reduce the fuel consumption when the conventional hydrocarbon fuels are substituted with hydrogen. In order to conduct the optimization process, an artificial neural network coupled with the design of the experiment concept was employed to identify the RCCI combustion mathematical model and provide the required population for two optimization algorithms, namely genetic algorithm, and particle swarm optimization algorithm. The results from the optimization process show that by advancing the diesel fuel injection along with the appropriate amount of exhaust gas recirculation and nitrogen as diluents, the level of EURO VI for NOx can be met. However, the losses in the RCCI engine output power is less than 5% meanwhile the gross indicated efficiency is over 50% and the reduction in hydrocarbon fuels consumption is about 40%.