Unburned Hydrocarbon Concentrations Research Articles

Allometry of nanoparticles in diesel-biodiesel blends for CI engine performance, combustion and emissions

Most countries in the world are facing two major challenges, one is the increase in the demand for energy consumption difficult to fulfill because of limited fossil fuel, and the second is the emission norms specified by many countries. Various methods are adopted to reduce emissions from engines but that leads to sacrificing the performance of CI engines. To eradicate this problem in the present study, the nanoparticles like (TiO2) are used with different particle sizes 10–30 nm, 30–50 nm and 50–70 nm induced in B20 (20% biodiesel and 80% diesel) with the constant volume fraction of 100 ppm, and utilized in the diesel engine without any modifications. The results showed that the incorporation of TiO2 nanoparticles improves the combustion of hydrocarbons and reduces the emissions of CO, unburned hydrocarbon concentration, NOx and soot. Moreover, among three sizes of the nanoparticles, those with size 30–50 nm showed interesting results with the reduction in brake-specific energy consumption, NOx, smoke and HC by 2.9%, 16.2%, 35% and 10%, respectively, com-pared to other blends used in the study, and hence the blend with the nanoparticle of size 30–50 nm is expected to be a more promising fuel for commercial application in CI engines.

Assessment of a complete truck operating under dual-mode dual-fuel combustion in real life applications: Performance and emissions analysis

The dual-mode dual-fuel (DMDF) strategy has been demonstrated to be a potential combustion mode to cover all the engine map with low-to-moderate NOx and soot emissions and high efficiency simultaneously. This can be accomplished by modifying the injection strategy to promote a fully premixed or a dual-fuel diffusive combustion depending on the operating conditions. The main limitation of the DMDF are the high concentrations of unburned hydrocarbons and carbon monoxide coupled with low exhaust temperatures, which can be a challenge for the stock diesel oxidation catalyst (DOC). Moreover, the use of a diffusive combustion combined with high EGR rates to avoid mechanical issues at high load enhances the soot formation, which can compromise the final soot levels in a homologation cycle. To evaluate these aspects, this work studies the performance and emissions of a DMDF truck concept along a WHVC and different in-service conformity cycles through vehicle systems simulations. For both types of cycles, five payloads were tested (0%, 25%, 50%, 75% and 100%) to evaluate the impact of this parameter on the operating points distribution inside the DMDF map. The first results show that the DMDF concept provides engine-out NOx levels below the EUVI regulation at normative payload (50%) with similar fuel consumption than the conventional diesel truck. On the other hand, the engine-out HC and CO emissions exceed their respective limits in all the cases, while the engine-out soot emissions only reach the EUVI levels up to 25% payload. By this reason, the stock DOC and diesel particulate filter from the conventional diesel truck were modelled and fitted to the DMDF truck model. The results evidenced that the use of these two ATS allows to achieve the EUVI limits in terms of tailpipe HC, CO and soot independently on the cycle and payload analyzed. Moreover, considering the tailpipe emissions values achieved with ATS at 50% payload, it can be inferred that both devices could be downsized for the DMDF application as compared to the conventional ATS for diesel applications.

Hydrogen as a Combustion Enhancer for Highly Efficient Ultra-Lean Spark-Ignition Engines

<div class="section abstract"><div class="htmlview paragraph">Performance of lean burn gasoline spark-ignition engines can be enhanced through hydrogen supplementation. Thanks to its physicochemical properties, hydrogen supports the flame propagation and extends the dilution limits with improved combustion stability. These interesting features usually result in decreased emissions and improved efficiencies which is of the utmost importance for future SI engines targeting ultra-lean conditions at λ ≥ 2 and brake thermal efficiencies above 50%. Compared to previous studies of hydrogen supplementation, this article aims at demonstrating how hydrogen can support the combustion process with a modern combustion system optimized for extreme dilution rates and high efficiency.Experimental investigations performed with a single cylinder engine are reported and show that the minimal amount of hydrogen required to reach λ = 2 is in the range of 2 to 4% of the total intake volume flow rate. At low load, NOx emissions can be lowered down to 33 ppm at λ = 2 and results also show that a10-fold decrease in NOx emissions is possible when the dilution rate increases from the lean limit without hydrogen up to λ = 2. In those ultra-lean conditions, particle emissions are also significantly lowered. Unburned energy is around 5% in low load conditions at λ = 2 but the engine-out unburned hydrocarbon concentration is maintained at an acceptable level. At high load, combustion timings can be improved thanks to the increase in the maximal dilution rate and to the better auto-ignition resistance of hydrogen. Consequently, the indicated efficiency is increased by more than 6% abs. compared to the reference stoichiometric conditions. Finally, a maximal indicated efficiency of 47.0% is obtained at λ = 2 with 3% of hydrogen at 3000 rpm - 13 bar IMEP. For this operating point, similar performance are obtained with a dual air/EGR dilution.</div></div>

Flame behavior and thermal structure of combusting plane jets with and without self-excited transverse oscillations

The flame behavior and thermal structure of combusting plane jets with and without self-excited transverse oscillations were investigated experimentally. The transversely-oscillating plane jet was generated by a specially designed fluidic oscillator. Isothermal flow patterns were observed using the laser-assisted smoke flow visualization method. Meanwhile, the flame behaviour was studied using instantaneous and long-exposure photography techniques. Temperature distributions and combustion-product concentrations were measured using a fine-wire type R thermocouple and a gas analyzer, respectively. The results showed that the combusting transversely-oscillating plane jets had distributed turbulent blue flames with plaited-like edges, while the corresponding combusting non-oscillating plane jet had laminar blue-edged flames in the near field. At a high Reynolds number, the transversely-oscillating jet flames were significantly shorter and wider with shorter reaction-dominated zones than those of the non-oscillating plane jet flames. In addition, the transversely-oscillating combusting jets presented larger carbon dioxide and smaller unburned hydrocarbon concentrations, as well as portrayed characteristics of partially premixed flames. The non-oscillating combusting jets presented characteristics of diffusion flames, and the transversely-oscillating jet flame had a combustion performance superior to its non-oscillating plane jet flame counterpart. The high combustion performance of the transversely-oscillating jets was due to the enhanced entrainment, mixing, and lateral spreading of the jet flow, which were induced by the vortical flow structure generated by lateral periodic jet oscillations, as well as the high turbulence created by the breakup of the vortices.

Extended operability of a commercial air-staged burner using a synthetic mixture of biomass derived gas for application in an externally fired micro gas turbine

Biomass gasification converts solid biomass into a gaseous fuel that is more versatile and can be used in many applications. However, biomass gasification gas contains some contaminants and inert compounds. The contaminants can cause several problems in the downstream equipment and undesirable emissions while the inert compounds can affect the lower heating value of the gas. Because of these characteristics, there have been difficulties in finding a conversion technology using biomass gasification gas for heat and power generation. In this regard, externally fired gas turbines open a possibility for this combustible gas since due to its configuration, combustion takes place outside the conventional gas turbine cycle. For this reason, combustion studies of biomass derived gas are important. In this work the operability of a commercial air-staged natural gas burner is shown in terms of CO, UHC, and NOX emissions using a synthetic mixture of biomass gasification gas. Two fuel gas mixtures simulating the composition of biomass gasification gas are injected in the combustor. Each fuel gas contains different injection rates of benzene in order to represent tars and to understand their effect on the combustion performance. Additionally, the equivalence ratio is varied in a range of lean conditions in order to find an optimum operation point for the burner studied. The results showed that the presence of polyaromatic hydrocarbons such as benzene reduced the CO concentrations in the exhaust gas while it increased the concentrations of unburned hydrocarbons (UHC) at equivalence ratios lower than 0.68. Additionally, NOX emissions showed a relatively constant trend over the range of equivalence ratios studied for both fuels. It was also observed that NOX emissions increase with the addition of benzene in the fuel gas. An optimum point with regards CO and UHC concentrations was found for the fuels tested.

Experimental and Computational Investigations for Combustion, Performance and Emission Parameters of a Diesel Engine Fueled with Soybean Biodiesel-Diesel Blends

In this work experimental and theoretical investigations were carried out on a single cylinder, direct injection diesel engine operating on different blends of a soybean methyl ester (SME) with diesel fuel. The effect of blending on the cylinder pressure, heat release rate, carbon monoxide (CO), unburned hydrocarbon (UHC), nitrogen oxides (NOx), and smoke opacity were measured. The results indicate that the use of biodiesel produces lower smoke opacity up to 48.23% with 14.65% higher brake specific fuel consumption (BSFC) compared to diesel fuel. The measured CO emissions of B20% SME and B100% SME were found to be 11.36% and 41.7% lower than that of diesel fuel respectively. All blends of SME were found to emit significantly lower UHC concentration compared to that of diesel over the entire load. NOx emissions are observed to be higher for all blends of SME. The experimental results are compared with the results of Diesel-rk software and a good agreement between them is noticed.

Engine performance and emission analysis of LPG-SI engine with the aid of artificial neural network

Artificial neural network (ANN) technique is used in this analysis to estimate the performance and emission concentration of liquefied petroleum gas (LPG) spark-ignition (SI) engine. The performance indicators include fuel consumption and brake thermal efficiency while the emission components are NO x, CO, CO2, O2, and unburned hydrocarbon (UHC). Data of engine body temperature and exhaust gas temperature are also simulated. The first part of this study involves experimental works where a single-cylinder four-stroke SI engine was modified to allow the intake of LPG and operated at variable loadings with constant speed. The experimental results show that LPG produces comparable performance at high loads while significant reduction takes place in NO x, CO, CO2, O2, and UHC concentrations. The second part of this study involves the use of back-propagation algorithm for the training of the ANN model. The result of the simulation reveals that ANN model is appropriate to estimate the engine performance and gas exhaust emissions with correlation coefficient ranging from 0.9 to 0.99 with low root mean-squared error and low mean relative error.

Innovative study of co-axial normal and inverse diffusion flames

An experimental work was performed to investigate the co-axial normal/inverse diffusion flames at both unbound and confined conditions. Three novel burner designs were employed such that initially co-axial air and fuel streams issuing from an inverse flame burner port were combusted within a confinement and then mixed with an outer atmosphere thus involving an outer normal flame. Strongly turbulent conditions were enforced through flow restriction, introducing cross-flow opposing jets, extending the aerodynamic expanding zones, and jet splitting. Such parametric variation was coupled with changes in the flow areas and relative velocities. With the vertically straight design, decreasing the covering plate punching diameter or its separation gap above the supplying air tube significantly decreased the exhausted unburned hydrocarbon concentrations. Sufficiently high air jet velocities led to lifted flames with an associated fuel entrainment. The peak flame temperature reduction to around 1300 °C highlighted the decrease in the maximum NOx concentrations. Enhanced qualitative/quantitative flame characteristics were also obtained upon employing an expanding interior wall design. The fuel/air mixing and recirculation were significantly enhanced by extending the confining wall such that the combustion efficiency was optimized by the flow dynamics of the inverse flame inner air supply. The maximum unburned hydrocarbon and carbon monoxide concentrations were 0.57 per cent and 800 ppm, respectively. In the third design, the mixing rates were increased by splitting the fuel jet so that the enlarged flame envelope increased the combustion efficiency at the proper relative jet velocities. The turbulence characteristics were computationally addressed by highlighting the role of jet shear layers and recirculation in augmenting the combustion efficiency and stability.

Experimental study of the effect of top-ring clearance volume on unburned hydrocarbon concentrations

The clearance volume between the piston, the cylinder and the top compression ring in an internal combustion engine has a significant effect on the unburned hydrocarbon concentration. The high heat transfer from the burning mixture to the cylinder surface extinguishes the flame front, and this is the main reason for increased unburned hydrocarbon concentrations. The heat transfer between the mixture and the clearance volume surface is affected by the ratio of coolant surface to the clearance volume. In this study the effect of the ratio of the coolant surface to the clearance volume on the unburned hydrocarbon concentration was investigated using three different purpose-built pistons. A decrease of this ratio reduced the unburned hydrocarbon concentration by 40%.

Injection of a H 2O 2/water solution into the combustion chamber of a direct injection diesel engine and its effect on soot removal

Hydrogen peroxide (H2O2) dissolved in water was injected into the combustion chamber of a direct injection (DI) diesel engine at different crank angles. Its effect on the general combustion characteristics was followed by crank angle (CA) resolved pressure and OH radiation measurements inside the combustion chamber. The influence on soot mass in the exhaust gas flow was measured by the Bosch Smoke Number, which is the stadard measurement technique in internal combustion engine research. Additionally, the concentrations of unburned hydrocarbons (HC) and nitric oxides (NOx) were recorded by a gas analyzer. For both, the spray of H2O2/water and pure water, a clear decrease in soot emission was observed for early injection at crank angles −40°<CA<−10o before top dead center (BTDC), which is associated with an increase in the exhaust gas HC concentration. For these conditions, the soot removal is mainly an effect of compressed air coolig, which increases the induction time of the diesel spray, thus resulting in a shift toward more premixed combustion. At injection crank angles CA>+10o, the water and the H2O2/water sprays show an opposite behavior with respect to the exhaust gas soot. The in-cylinder measurements clearly show an increase of OH radiation during cycles with H2O2/water injection compared to the standard engine conditions. The H2O2 decomposition product OH influencs the chemistry of the in-cylinder soot oxidation, which results in a decrease of the soot mass in the engine exhaust gas flow. Concentrations of HC and NOx are not significantly affected. The addition of pure water causes an increase in the exhaust gas soot for spray injection crank angles CA <+10o.

A constrained iterative deconvolution technique with an optimal filtering: application to a hydrocarbon concentration sensor

A deconvolution method for estimating unburned hydrocarbon concentration in boiler smokes is presented. In order to qualify a boiler regarding to the ecological European Standards an iterative constrained estimation algorithm including a filtering step has been set up. The application of such technique to both synthetic signals and experimental data has shown its robustness in regard to measurement noise and its reliability to restore a signal.

Waste water combustion in laboratory swirl burners—I. Arrangements and burning conditions

In a series of three papers we report on laboratory experiments of waste water combustion with dissolved N- and S-compounds sprayed into a confined swirl flame. The aims are to measure the NO formation under various operating conditions and to study the interaction of NO and SO 2 formation in flames with water injection. In the present paper the experimental equipment, the sampling systems, and the diagnostics are described. Two types of burners, which mainly differ in the method of waste water injection, were used. The spray characteristics of the nozzles and the droplet evaporation process could be measured. The temperature and the axial flow velocity distribution together with CO and unburned hydrocarbon concentration measurement characterizes the global flow and combustion process. Thermal NO concentrations measured in the two types of burners under pure water injection conditions serve as a reference level for the subsequent N-doped water results.

Flame quenching and unburned hydrocarbons on the wall of a spherical combustion vessel.

An experimental study on one-dimensional, laminar flame quenching on a cold wall was described herein. A homogeneous mixture of propane-air was ignited at the center of a spherical vessel, and the effects of pressure, mixture ratio and vessel size on the heat flux to the wall and on the unburned hydrocarbon concentrations were investigated. The characteristic values of quenching layer thickness defined from the maximum heat flux and the unburned hydrocarbon concentrations, δq and δHC, respectively, were determined. The value of δq was proportional to about minus 0.45 of the power of the pressure and was independent of the mixture ratio and the size of the combustion vessel. It was recognized that in the large size vessel, the hydrocarbons in the quench layer after the completion of combustion with flame propagation were oxidized. The value ofδHC obtained in the small size vessel was proportional to δq.

Operation of carburetor engines on water/gasoline emulsions

The 1500-cm/sup 3/ engine was tested on AI-93 gasoline and on water/gasoline emulsions (WGEs) with the following compositions: a) 10% water, 1% nonionic surfactants, remainder AI-93 gasoline; b) 20% water, 2% surfactants, remainder AI093 gasoline; c) 40% water, 3% surfactants, remainder A-76 gasoline. Attempts to determine the optimal content of water in the WGE, and to evaluate the feasibility of increasing the engine efficiency (e.g., improving the fuel economy by the use of the WGE). Finds that it is desirable to adjust the engine according to the quantity of added water, depending on the operating conditions, so as to utilize the effect of the water on the gasoline knock resistance and thus avoid a drop in the economy indices and an increase in the unburned hydrocarbon concentration obtained during idling, warmup, and operation at low loads, which are unavoidable when burning a WGE of constant composition.

Factors affecting NO x formation from nitrogen-containing fuels

Data from a turbulent diffusion flame burner indicate that the summation of fixed-nitrogen species (NO + HCN + NH i ) is a significant measure of a flame's emission potential. Raising the flame temperature by preheating of the inlet air causes a reduction in the summation of fixed-nitrogen species in rich flames. This reduction occurs over only a narrow range of equivalence ratios and only for flame conditions with low concentrations of unburned hydrocarbons at burner exhaust. Therefore, the fuel and air must be intensely mixed at the entrance of the burner. Flames resulting in soot formation heavy enough to turn the flame bright yellow yield high concentrations of unburned hydrocarbons and HCN. For rich flames this results in a high summation of fixed-nitrogen species, because HCN is the dominant nitrogen containing species of these flames. The distribution of fixed-nitrogen species leaving the burner is independent of the form of the nitrogen in the fuel; the reduction of fixed-nitrogen species with increased air preheat occurs at fuel nitrogen concentrations as high as 5%.

Oxides of Nitrogen from Gas Turbines

Experimental and theoretical studies were made to provide information on nitrogen oxide concentrations produced by gas turbine engines. Nitric oxide concentrations of from 100 to 350 ppm, adjusted to stoichiometric conditions, were measured in aircraft turbojet engines. Concentrations of less than 50 ppm, similarly adjusted, were measured in a 60 hp industrial gas turbine. Concentrations of about 100 ppm, also adjusted, were measured in a laboratory combustor of a design similar to gas turbine combustors. Carbon monoxide and unburned hydrocarbon concentrations also were determined. Comparison with predicted equilibrium concentrations shows strong departures from equilibrium.

The Influence of Vehicle Operating Variables on Exhaust Emissions

This paper is a report of the operating variables and emission characteristics of a 1964 283 cubic inch V-8 Chevrolet automobile. This vehicle was used as a laboratory tool in a project to develop an improved driving cycle to represent Los Angeles peak hour driving. As a result it became necessary to run many exploratory tests to determine the relationships between the primary variables of intake manifold vacuum, engine rpm, and vehicle speeds and acceleration rates. Emissions of hydrocarbons, carbon monoxide, and nitrogen oxides were also determined for the entire range of operating conditions. The effect of prior operating modes on closed-throttle unburned hydrocarbon concentrations was also determined. The results of these tests are presented in tables and graphs which make a comprehensive picture of one typical automobile as a generator of air pollutants.