Combustion Evolution Research Articles

A New Simple Function for Combustion and Cyclic Variation Modeling in Supercharged Spark Ignition Engines

Research in the field of Internal Combustion (IC) engines focuses on the drastic reduction of both pollutant and greenhouse gas emissions. A promising alternative to gasoline and diesel fuel is represented by the use of gaseous fuels, above all green hydrogen but also Natural Gas (NG). In previous works, the authors investigated the performance, efficiency, and emissions of a supercharged Spark Ignition (SI) engine fueled with mixtures of gasoline and natural gas; a detailed research involving the combustion process of this kind of fuel mixture has been previously performed and a lot of experimental data have been collected. Combustion modeling is a fundamental tool in the design and optimization process of an IC engine. A simple way to simulate the combustion evolution is to implement a mathematical function that reproduces the mass fraction burned (MFB) profile; the most used for this purpose is the Wiebe function. In a previous work, the authors proposed an innovative mathematical model, the Hill function, that allowed a better interpolation of experimental MFB profiles when compared to the Wiebe function. In the research work presented here, both the traditional Wiebe and the innovative Hill function have been calibrated using experimental MFB profiles obtained from a supercharged SI engine fueled with mixtures of gasoline and natural gas in different proportions; the two calibrated functions have been implemented in a zero-dimensional (0-D) SI engine model and compared in terms of both Indicated Mean Effective Pressure (IMEP) and cyclic pressure variation prediction reliability. It was found that the Hill function allows a better IMEP prediction for all the operating conditions tested (several engine speeds, supercharging pressures, and fuel mixtures), with a maximum prediction error of 2.7% compared to 4.3% of the Wiebe function. A further analysis was also performed regarding the cyclic pressure variation that affects all the IC engines during combustion and may lead to irregular engine operation; in this case, the Hill function proved to better predict the cyclic pressure variation with respect to the Wiebe function.

Effect of initial turbulence on explosion behavior of stoichiometric methane-ethylene-air mixtures in confined space

The turbulent explosion process of stoichiometric CH4/C2H4/air mixtures was experimentally studied by using a standard 20 L sphere explosion system and it’s powder storage tank as the turbulence generator. Taking the initial turbulent environment and ethylene volume fraction as variables, the effects of turbulence intensity and fuel composition on explosion characteristics were studied. The results show that both turbulence intensity and ethylene content promote the explosion of the mixtures and increase the severity of the explosion, but the influence of turbulence intensity on combustion evolution mainly focuses on heat loss, while the influence of ethylene content mainly focuses on adiabatic explosion. When the ethylene ratios increase to 0.5 or more, the increase of explosion severity caused by turbulence is not obvious. The analysis of experimental results and numerical simulation shows that the influence of initial turbulence generated by powder storage tank on explosion is the result of the combined action of turbulent kinetic energy and combustible gas redistribution.

Numerical Investigation of Contact Burning in an Air-Breathing Continuous Rotating Detonation Engine

Three-dimensional (3D) numerical simulations of a continuous rotating detonation engine are carried out with an unsteady Reynolds-averaged Navier-Stokes solver. The second-order upwind advection upstream splitting method and second-order Runge-Kutta method are used to discretize space and time terms, and detailed 9-species 19-step hydrogen-oxygen reactions are applied in this study. Nonpremixed rotating detonation is successfully realized numerically, and the characteristics of the detonation wave are revealed. The expanding angle of the combustor has a great impact on the shape of the detonation wave but has little influence on the propagation velocity. The evolution of combustion on the contact region is analyzed in detail; a more accurate schematic of non-premixed air-breathing rotating detonation engines is given in this paper. A rough analysis of the heat performance of the contact region shows that the heat release of the contact region is approximately one-third of the total heat release and the configurations of the combustors do not affect the proportion.

Onset of Oblique Detonation Waves for a Cavity-Based Wedge

To shorten the ignition length of the wedge-induced oblique detonation wave, a geometric setup in which the leading and aft wedges are connected by a cavity is proposed. High-resolution viscous computations to solve the reactive Reynolds-averaged Navier–Stokes equations have been performed, which examine the onset and evolution of combustion and flow configuration with premixed mixtures of inflow Mach numbers ranging from 4.0 to 6.0. The unreactive flowfield of the cavity-based wedge is analogous to that of a sole cavity with the exclusion of shock/shock interaction downstream. For and 5.0, no sustainable oblique detonation wave is achieved, and the flame holds in the cavity and near-wall area of the aft wedge; however, a short-lived detonation wave triggered by the shock focuses is observed during the combustion procedure with . For , nearly direct detonation initiation of postshock occurs, and an oblique detonation wave is established above the fore edge of the cavity. Unexpectedly, a delayed ignition downstream contributes to the development of a recirculation zone, which results in a detached oblique detonation wave for .

Structural evolution and opto-electrical characterization of auto-ignited combustion synthesized LaSmZr2O7 ceramic

Lanthanide Zirconates with Ln2Zr2O7 composition are of great research interest due to their multifunctional applications. We report the synthesis of LaSmZr2O7, a rarely studied compound, its structural, optical, and electrical characteristics, along with its structural evolution at different temperatures. Nanocrystalline LaSmZr2O7 powder is synthesized through an auto-ignited combustion method. The compound shows phase transition from defect fluorite to pyrochlore over an annealing temperature of 850 °C–1200 °C. It has high absorbance in the UV region, high reflectance in the visible region, and wide optical bandgap energy. The optical band gap is observed to increase with defect fluorite to the pyrochlore phase transition. A bulk LaSmZr2O7 pellet of high density is obtained at a sintering temperature of 1500 °C for a soaking time of 2 hours. Impedance spectroscopic study revealed pure oxide-ion conductivity of the compound in the 550 °C–850 °C temperature range with a conductivity value of 2.04 × 10−2 S/m at 850 °C.

Effect of fuel quality on combustion evolution and particle emissions from PFI and GDI engines fueled with gasoline, ethanol and blend, with focus on 10–23 nm particles

The European Commission is planning to lower the particle cut off size down to 10 nm to consider the contribution of the sub-23 nm particles. Within the European project Sureal-23, a comprehensive study on the sub-23 nm particles was performed and novel technologies for their sampling and measurement were developed. One new proposed instrument, the Half Mini Differential Mobility Analyser (HM-DMA), was used in the present study. The investigation was carried out on a small direct/port fuel injection, spark ignition engine fueled with gasoline, ethanol and a 30 %v/v ethanol blend. Results highlighted a general reduction of the number and the size of the particles emitted by pure ethanol. The effect of the ethanol blend on sub-23 nm particle emissions was affected by the operating condition and the injection strategy. The extent of the VOF depends on the fuels as well as on the engine configuration and operating condition. Some differences were noted between the results from EEPS and HM-DMA ascribable to the different measurement principle and to the processes occurring in the dilution system.

Effect of Cylinder-by-Cylinder Variation on Performance and Gaseous Emissions of a PFI Spark Ignition Engine: Experimental and 1D Numerical Study

Combustion stability, engine efficiency and emissions in a multi-cylinder spark-ignition internal combustion engines can be improved through the advanced control and optimization of individual cylinder operation. In this work, experimental and numerical analyses were carried out on a twin-cylinder turbocharged port fuel injection (PFI) spark-ignition engine to evaluate the influence of cylinder-by-cylinder variation on performance and pollutant emissions. In a first stage, experimental tests are performed on the engine at different speed/load points and exhaust gas recirculation (EGR) rates, covering operating conditions typical of Worldwide harmonized Light-duty vehicles Test Cycle (WLTC). Measurements highlighted relevant differences in combustion evolution between cylinders, mainly due to non-uniform effective in-cylinder air/fuel ratio. Experimental data are utilized to validate a one-dimensional (1D) engine model, enhanced with user-defined sub-models of turbulence, combustion, heat transfer and noxious emissions. The model shows a satisfactory accuracy in reproducing the combustion evolution in each cylinder and the temperature of exhaust gases at turbine inlet. The pollutant species (HC, CO and NOx) predicted by the model show a good agreement with the ones measured at engine exhaust. Furthermore, the impact of cylinder-by-cylinder variation on gaseous emissions is also satisfactorily reproduced. The novel contribution of present work mainly consists in the extended numerical/experimental analysis on the effects of cylinder-by-cylinder variation on performance and emissions of spark-ignition engines. The proposed numerical methodology represents a valuable tool to support the engine design and calibration, with the aim to improve both performance and emissions.

Thermal Properties and Key Groups Evolution of Low-Temperature Oxidation for Bituminous Coal under Lean-Oxygen Environment.

To deeply explore the spontaneous combustion disaster of coal caused by air leakage and oxygen supply, low-temperature coal oxidation experiments under different oxygen concentrations (DOC) were carried out. Within the coal spontaneous combustion characteristic measurement system, a synchronous thermal analyzer (STA) and a Fourier transform infrared spectrometer (FTIR), the macro laws of gas and heat generation under DOC are analyzed, and the mechanism of the development of coal spontaneous combustion restricted by the lean-oxygen environment is also revealed. The results show that the change of oxygen concentration (OC) does not affect the critical temperature value and gas index change trend, but the lean-oxygen environment reduces the gas concentration and heat production rate very obviously. According to the temperature of the intersection, OC needs to be lowered to less than 5% when preventing spontaneous combustion of coal. The chain thermal reaction lags in the lean-oxygen environment, and the pyrolysis activity is significantly reduced. Meanwhile, the temperature points at T6 and T7 show significant differences. Furthermore, with increasing OC and temperature, the content of the aliphatic hydrocarbon presents an overall trend of first increasing, then decreasing, and continuously increasing after stage IV. It is concluded that •OH, aliphatic hydrocarbons, aromatic hydrocarbons, and carboxyl groups are the key groups for the coal spontaneous combustion evolution under DOC. To combine the spontaneous combustion reaction of coal in the DOC environment, the reaction path of the index gas in the macroscopic phenomenon and the reason for the concentration differences are revealed, the mechanism for exotherm varies caused by OC is clarified, and the microscopic inhibition affection on the chain reaction within the lean-oxygen environment is also explored. The results put forward the key groups evolution mechanism under the DOC for coal oxidation, which could provide the technical guidance for the fire prevention and control on coal mines.

Reaction pathways and cyclic chain model of free radicals during coal spontaneous combustion

Reactions of free radicals play essential roles in the evolution of the spontaneous combustion of coal. However, their elementary reaction pathways and details during this process have not been revealed by far. This paper established reaction pathways of free radicals during coal spontaneous combustion based on typical active free radicals by quantum chemistry method. The specific structural parameters and thermodynamic data for reactions (R1 ~ R9) are calculated to reveal the reaction process. The cyclic model of free radicals during coal self-heating has been proposed for the first time. The results indicate that most of the reactions involved in free radicals are exothermic reactions with heat release ranging from 7.568 ~ 167.113 kJ/mol. The initial reactions (R1 and R2) can accumulate heat and generate active peroxide free radical (R-O-O) as well as hydroxyl radical (OH). Both of them can occur easily at the normal temperature. The heat release increases the ambient temperature, which causes non-spontaneous reactions to proceed successively. The decomposition of peroxide free radicals triggers the reaction pathways of the cyclic model. The hydroxyl radical can lead to the reaction with active sites in coal, which can accumulate plenty of heat and supply the R for initiating reaction R(1) in the cycle. Both hydroxyl radicals and hydrocarbon radicals play vital roles in consuming active groups in coal and oxygen continuously. The results demonstrate that to fundamentally prevent coal spontaneous combustion, it is necessary to eliminate the key active free radicals (R, R-O-O, and OH) to terminate the cyclic chain reaction.

Procedure for constructing a mathematical model to determine the time of the initial stage of fire evolution

To develop appropriate measures and means of fire protection at facilities, it is relevant to form an idea of the phenomenology of the processes of the occurrence, evolution, and termination of combustion. This paper proposes procedures for building mathematical models of the energy component of those physicochemical processes that occur in wood under the influence of fire, which make it possible to determine the time from the beginning of such an impact to the onset of the phase of flame combustion. The adequacy of mathematical modeling was tested experimentally at a standardized installation for studying flame propagation over the surface of wood. The samples used for the reported theoretical and experimental studies were the specimens of unprotected wood made from 20-mm-thick pine sapwood with a density of 400‒550 kg/m3. The samples of fireproof wood (of the same variety, thickness, and density) were impregnated with a fire retardant based on diammonium phosphate and ammonium sulfate (at consumption of 168.2 g/m2 of dry fire-retardant components). The modeling employed the results from the experimental determining of the ignition temperature of unprotected and fire-proof wood, specifically: 235 °C – for unprotected wood, 410 °C – for fire-proof wood, respectively. The results of mathematical modeling and experimental studies confirm the possibility of significant lengthening of time from the onset of fire exposure to the ignition of fire load from wood when nitrogen-phosphorus impregnating agents are used for fire protection. Procedures of mathematical modeling have been proposed to build models for determining the cooling effect from the use of impregnating fire retardants to protect the wood on the prolongation of the stage of a fire start. Mathematical modeling data could be applied when making impregnating fire retardants

Effect of a novel piston geometry on the combustion process of a light-duty compression ignition engine: An optical analysis

The development of new piston geometries has shown great potential to achieve the low levels of soot emissions required by regulation. Thus, the present paper aims to characterize the influence of a new piston design over combustion process. It is characterized by the introduction of protrusions around the periphery of the bowl, evenly spaced. The performance of this geometry is compared to other geometries that have been extensively analyzed in literature, under similar operating conditions. To achieve this objective, a single cylinder optical compression ignition engine was used with full-quartz pistons representing three bowl geometries: re-entrant, stepped lip and wave-stepped lip. Two optical techniques (OH∗ chemiluminescence and Natural Luminosity-NL) were applied for identifying the near-stoichiometric zones and the differences in the combustion evolution. The flame movement was analyzed by applying the combustion image velocimetry (CIV) algorithms. In addition, an in-cylinder pressure analysis was performed for each piston at 4.5 bar and 7.5 bar IMEP and the differences in terms of Rate of Heat Release were highlighted. A more intense reverse flow was clearly identified when using wave protrusions inside the bowl. The stepped lip and wave-stepped lip bowl present faster late cycle oxidation with much near-stoichiometric zones than re-entrant piston.

Spatiotemporal evolution of coal spontaneous combustion in longwall gobs: A case study from mining discontinuation to resumption

AbstractCoal mining is frequently halted for long periods of time due to geological faults, and the process of resuming mining is often fraught with danger. To address this issue, in this study, the previously developed COMBUSS‐3D software was optimized to simulate the process between mining discontinuation and resumption, based on the multi‐field coupling theory. The optimized software takes the temperature distribution in gobs when coal mining ends as the initial condition, and it considers the condition of spontaneous coal combustion after remining. The actual advance distance of the working face is introduced into the program compilation and solved by linear interpolation. These improvements ensure that the calculation results are more realistic. The results demonstrate that the high‐temperature zone is distributed on the air intake side of the gob, and its final location largely depends on the remining advance rate. The hazardous area of spontaneous ignition gradually moves to a deep suffocation zone of the gob when the mining of the coal wall resumes, the residual coal is no longer oxidized, and CO formation is gradually decreased, which is verified by the theoretical expectations and on‐site observations. The spontaneous combustion period can be effectively prolonged by reducing the thickness of crushed coal during the mining stage or by increasing the longwall advance rate after resuming mining. This study can provide significant guidance and suggestion on locating the hazardous area in gobs and suppressing the spontaneous coal ignition.

Thermal decomposition, phase evolution and morphology study of combustion synthesized alumina powder – Influence of precursor pH

Here, nanocrystalline alumina powder is prepared by the glycine-nitrate combustion method, maintaining stoichiometric fuel to oxidizer ratio and two different pH conditions. The in-situ exothermic reaction occurs between an oxidizer, and fuel found to be affected by the alkalinity of the precursor solution. During combustion synthesis, spontaneous ignition occurs with the generation of gases and foamy ashes. The ash crushed into powders and then calcined at different temperatures. Thermodynamic modelling is done to calculate the enthalpy of combustions and the number of moles of gases released from the stoichiometric chemical reactions. Different characterization techniques used to study the phase formation, surface area, microstructure and morphology of the ash and calcined alumina powders. Fine crystalline α - Al2O3 powder with high surface area formed in alkaline condition. Micrographs reveal that flaky morphology of the alumina powder changed to grain type on increasing the pH of the precursor solution.

Two-stage autoignition and combustion mode evolution in boundary layer flows above a cold flat plate

Boundary layers are omnipresent in fundamental kinetic experimental facilities and practical combustion engines, which can cause ambiguity and misleading results in kinetic target acquisition and even abnormal engine combustion. In this paper, using n-heptane as a representative large hydrocarbon fuel exhibiting pronounced low-temperature chemistry (LTC), two-dimensional numerical simulation is conducted to resolve the transient autoignition phenomena affected by a boundary layer. We focus on the ignition characteristics and the subsequent combustion mode evolution of a hot combustible mixture flowing over a colder flat plate in an isobaric environment. For cases with autoignition occurring within the boundary layer, similarity is observed in the first-stage ignition as manifested by a constant temperature at all locations. The first-stage ignition is found to be rarely affected by heat and radical loss within the boundary layer. While for the main ignition event, an obvious dependence of ignition process on boundary layer thickness is identified, where the thermal-chemical process exhibits similarity at locations with similar boundary layer thickness, and the main ignition tends to first occur within the boundary layer at the domain end and generates a C-shape reaction front. It is found that sequential spontaneous autoignition is the dominant subsequent combustion mode at high-pressure conditions. At low to intermediate pressures, auto-ignition assisted flame propagation is nevertheless the dominant mode for combustion evolution. This research identifies novel features of autoignition and the subsequent combustion mode evolution affected by a cold, fully developed boundary layer, and provides useful guidance to the interpretation of abnormal combustion and combustion mode evolution in boundary layer flows.

Surrogate model for improved simulations of small-scale sludge incineration plants

Although various modelling approaches exist for the simulation of solid fuel combustion, no specific model has been developed for the accurate description of gas-phase combustion in small-scale combustion devices. This is particularly limiting in scenarios when volatile-rich, complex and incompletely described solid fuels such as sewage sludge are used. To address this issue, an accurate description of combustion from the fuel bed onwards is required as well as an improved description of emitted volatiles. This paper introduces an innovative surrogate-based combustion model that combines data on sludge devolatilisation and measured combustion characteristics to offer a new surrogate composition. The composition includes heavy hydrocarbon species to accurately describe combustion evolution. A sensitivity analysis revealed that H2 contributes significantly to combustion evolution, while the most robust surrogate composition is obtained when ethanol is used as a leading representative of heavier hydrocarbons. The model can be used to produce suitable surrogates for the main sludge combustion interval, offering the required improvement in fuel descriptions and accuracy of simulations in the vicinity of the fuel bed. Hence, this model is particularly suitable for the optimisation of temperature, heat release rate, and concentration field in combustion chambers with limited volumes.

1D Simulation and Experimental Analysis on the Effects of the Injection Parameters in Methane–Diesel Dual-Fuel Combustion

Notwithstanding the policies that move towards electrified powertrains, the transportation sector mainly employs internal combustion engines as the primary propulsion system. In this regard, for medium- to heavy-duty applications, as well as for on- and off-road applications, diesel engines are preferred because of the better efficiency, lower CO2, and greater robustness compared to spark-ignition engines. Due to its use at a large scale, the internal combustion engines as a source of energy depletion and pollutant emissions must further improved. In this sense, the adoption of alternative combustion concepts using cleaner fuels than diesel (e.g., natural gas, ethanol and methanol) presents a viable solution for improving the efficiency and emissions of the future powertrains. Particularly, the methane–diesel dual-fuel concept represents a possible solution for compression ignition engines because the use of the low-carbon methane fuel, a main constituent of natural gas, as primary fuel significantly reduces the CO2 emissions compared to conventional liquid fuels. Nonetheless, other issues concerning higher total hydrocarbon (THC) and CO emissions, mainly at low load conditions, are found. To minimize this issue, this research paper evaluates, through a new and alternative approach, the effects of different engine control parameters, such as rail pressure, pilot quantity, start of injection and premixed ratio in terms of efficiency and emissions, and compared to the conventional diesel combustion mode. Indeed, for a deeper understanding of the results, a 1-Dimensional spray model is used to model the air-fuel mixing phenomenon in response to the variations of the calibration parameters that condition the subsequent dual-fuel combustion evolution. Specific variation settings, in terms of premixed ratio, injection pressure, pilot quantity and combustion phasing are proposed for further efficiency improvements.

Study on dual fuel combustion in an optical research engine by infrared diagnostics varying methane quantity and engine speed

Dual fuel combustion represents a possible solution for decreasing the emission produced by diesel engine, while maintaining the efficiency rate at comparable values. In this activity, methane and diesel are used for dual fuel combustion. Methane is injected in the intake manifold, when the intake valves are closed; meanwhile the diesel is delivered directly into the cylinder. The aim of this work is to study the effect of increasing methane concentration at two engine speeds (1500 and 2000 rpm, respectively), on the start and evolution of dual fuel combustion in a compression ignition research engine using infrared diagnostics.Infrared diagnostic has the advantage of being not intrusive, it gives a high spatial and temporal resolution of combustion phenomenon and it is able to qualitatively identify the local concentration of chemical species. Infrared camera detects the energy that the target emits as electromagnetic waves from 3 to 5.5 μm wavelength. Hence, no light sources or multiple optical accesses are needed; and commercial fuels can be used because they emit in the infrared as well.In the experiments, two filters are adopted to follow the whole combustion phenomenon from injection of diesel fuel to late combustion phase with high spatial and temporal resolution. Using the band-pass 3.3 μm, qualitative information about fuel vapour distribution and ignition location during low and high temperature heat release has been provided. Moreover, the combustion evolution is investigated by means of the band-pass filter at 4.2 μm, which is the characteristic of the asymmetric stretch of the CO2 molecule. In particular, autoignition and combustion evolution of the DF combustion are investigated increasing premixed ratio of methane. Differences with the conventional diesel combustion are highlighted. Diesel is the driven fuel that manages the autoignition and combustion of the DF mode in the investigated test cases.

Dynamic projection of anthropogenic emissions in China: methodology and 2015–2050 emission pathways under a range of socio-economic, climate policy, and pollution control scenarios

Abstract. Future trends in air pollution and greenhouse gas (GHG) emissions for China are of great concern to the community. A set of global scenarios regarding future socio-economic and climate developments, combining shared socio-economic pathways (SSPs) with climate forcing outcomes as described by the Representative Concentration Pathways (RCPs), was created by the Intergovernmental Panel on Climate Change (IPCC). Chinese researchers have also developed various emission scenarios by considering detailed local environmental and climate policies. However, a comprehensive scenario set connecting SSP–RCP scenarios with local policies and representing dynamic emission changes under local policies is still missing. In this work, to fill this gap, we developed a dynamic projection model, the Dynamic Projection model for Emissions in China (DPEC), to explore China's future anthropogenic emission pathways. The DPEC is designed to integrate the energy system model, emission inventory model, dynamic projection model, and parameterized scheme of Chinese policies. The model contains two main modules, an energy-model-driven activity rate projection module and a sector-based emission projection module. The activity rate projection module provides the standardized and unified future energy scenarios after reorganizing and refining the outputs from the energy system model. Here we use a new China-focused version of the Global Change Assessment Model (GCAM-China) to project future energy demand and supply in China under different SSP–RCP scenarios at the provincial level. The emission projection module links a bottom-up emission inventory model, the Multi-resolution Emission Inventory for China (MEIC), to GCAM-China and accurately tracks the evolution of future combustion and production technologies and control measures under different environmental policies. We developed technology-based turnover models for several key emitting sectors (e.g. coal-fired power plants, key industries, and on-road transportation sectors), which can simulate the dynamic changes in the unit/vehicle fleet turnover process by tracking the lifespan of each unit/vehicle on an annual basis. With the integrated modelling framework, we connected five SSP scenarios (SSP1–5), five RCP scenarios (RCP8.5, 7.0, 6.0, 4.5, and 2.6), and three pollution control scenarios (business as usual, BAU; enhanced control policy, ECP; and best health effect, BHE) to produce six combined emission scenarios. With those scenarios, we presented a wide range of China's future emissions to 2050 under different development and policy pathways. We found that, with a combination of strong low-carbon policy and air pollution control policy (i.e. SSP1-26-BHE scenario), emissions of major air pollutants (i.e. SO2, NOx, PM2.5, and non-methane volatile organic compounds – NMVOCs) in China will be reduced by 34 %–66 % in 2030 and 58 %–87 % in 2050 compared to 2015. End-of-pipe control measures are more effective for reducing air pollutant emissions before 2030, while low-carbon policy will play a more important role in continuous emission reduction until 2050. In contrast, China's emissions will remain at a high level until 2050 under a reference scenario without active actions (i.e. SSP3-70-BAU). Compared to similar scenarios set from the CMIP6 (Coupled Model Intercomparison Project Phase 6), our estimates of emission ranges are much lower than the estimates from the harmonized CMIP6 emissions dataset in 2020–2030, but their emission ranges become similar in the year 2050.

Influence of water injection on combustion identified through spectroscopy in an optical direct injection spark ignition engine

Within the context of increasing boost pressure and application of alternative methods for controlling knock, the present study scrutinized the effects of water injection on combustion characteristics and emissions. Conditions of wide open throttle and fixed spark timing were investigated in an optically accessible unit, that featured a UV-enhanced window-mirror combination fitted in an elongated piston configuration. Commercial gasoline was used in the direct injection fuel system, while water was delivered to the intake manifold. Engine performance was found to feature a slightly decreasing trend when increasing the injected water quantity in three steps, at 10, 20 and 30% of the mass flow of gasoline. Nonetheless, the maximum drop in indicated mean effective pressure was below 2%, even though the spark timing was kept constant. Changes in combustion stability were negligible. Thermodynamic analysis was coupled with cycle-resolved flame visualization and spectroscopy. The latter technique allowed the radiative emission related to sodium to be directly associated with the injected water quantity, thus allowing further detailed evaluations correlated with evaporation effects. Flame front characteristics confirmed minor effects on combustion evolution, with a slight increase of wrinkling when water flow was augmented. Finally, quasi-dimensional modelling allowed evaporated water quantities to be estimated at the time of ignition and during combustion.

1D numerical study on hydrogen injection enabling ultra-lean combustion in a small gasoline Spark Ignition engine

This paper deals with the effects of hydrogen port injection on combustion evolution, efficiency and exhaust emissions of a small turbocharged gasoline Spark-Ignition engine through a 1D numerical code. First, the experiments on the base engine architecture are performed at different speeds and at low/medium loads. The experimental findings are used to validate a 1D model of the whole engine, developed within a commercial code. 1D model is also refined with “user-defined” sub-models for an accurate description of the in-cylinder phenomena, namely turbulence, combustion, heat transfer, and emissions. In a second step, 1D model is virtually modified through the installation of an hydrogen injector in each intake runner, while the combustion sub-model also accounts for the impact of hydrogen addition on the laminar flame speed through a dedicated correlation. 1D simulations are performed at low/medium loads and fixed speed of 2250 rpm with 5% of hydrogen by volume in the intake air. Numerical investigations show that hydrogen addition to gasoline/air mixtures allows relevant efficiency benefits (up to a maximum percent gain of 19%), while the NO emissions are almost eliminated. Consequently, hydrogen-boosted combustion represents a potential solution to achieve very high efficiency and reduced pollutant emissions of gasoline spark ignition engines equipped with a conventional combustion system.