SEARCH · Engineering Papers

Results for “COMBUSTION”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

SourceResearch connectionFrom yearThrough year

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 361 records · Page 20

All sources NASA NTRS DOE OSTI

DOE OSTI2020

Spark-ignited direct-injection engine combustion systems

A direct-injection stratified charge internal combustion engine includes a combustion cylinder to receive an air-fuel mixture, and an air intake port to inlet air into the combustion cylinder. The direct-injection engine also includes a fuel injector configured to deliver fuel within the cylinder in a spray pattern substantially aligned to a cylinder central axis to create the air-fuel mixture. A spark igniter is located within a path of the spray pattern to ignite combustion of the air-fuel mixture. The direct-injection engine further includes a movable piston defining a lower boundary of the combustion cylinder to contain the combustion of the air-fuel mixture. The piston is configured to include a bowl portion having local geometric features located on an intake port side of the combustion cylinder to redirect fluid flow towards a vortex in fluid communication with a combustion location near the cylinder central axis.

42 ENGINEERING↗

DOE OSTI2015

Influence of radiation absorption by microparticles on the flame velocity and combustion regimes

Thermal radiation from hot combustion products has virtually no effect on the flame propagation in a gas medium. We consider a different situation when even a small concentration of microparticles suspended in a gas absorbs the thermal radiation and heats the gas mixture ahead of the combustion wave front by transferring it to the gas. The mixture heating ahead of the flame front can lead either to a moderate increase in the combustion wave velocity for a fast flame or to its significant increase for a slow flame, depending on the gas mixture reactivity and the normal laminar flame velocity. For a slow flame, the heat transfer by radiation from the combustion products can become the dominant mechanism compared to the ordinary molecular thermal conduction that determines the combustion wave structure and velocity. The radiative heating for a spatially nonuniform distribution of particles ahead of the flame front is shown to give rise to a temperature gradient that, in turn, can lead to the ignition of different combustion regimes, depending on the radiation absorption length. In accordance with the Zeldovich gradient mechanism, both deflagration and detonation regimes can be formed in this case. A hydrogen–oxygen flame is used as an example to illustrate the ignition of different combustion wave propagation regimes, depending on the radiation absorption length.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗

DOE OSTI2014

Measure Guideline: Combustion Safety for Natural Draft Appliances Using Indoor Air

This Measure Guideline covers how to assess and carry out the combustion safety procedures for appliances and heating equipment that uses indoor air for combustion in low-rise residential buildings. Only appliances installed in the living space, or in an area freely communicating with the living space, vented alone or in tandem with another appliance are considered here. A separate Measure Guideline addresses combustion appliances located either within the living space in enclosed closets or side rooms or outside the living space in an adjacent area like an attic or garage that use outdoor air for combustion. This document is for inspectors, auditors, and technicians working in homes where energy upgrades are being conducted whether or not air infiltration control is included in the package of measures being applied. In the indoor combustion air case, guidelines summarized here are based on language provided in several of the codes to establish minimum requirements for the space using simplified prescriptive measures. In addition, building performance testing procedures are provided by testing agencies. The codes in combination with the test procedures offer comprehensive combustion safety coverage to address safety concerns, allowing inexperienced residential energy retrofit inspectors to effectively address combustion safety issues and allow energy retrofits to proceed.

32 ENERGY CONSERVATION, CONSUMPTION, AND UTILIZATI↗

DOE OSTI2014

Combustion Safety for Appliances Using Indoor Air (Fact Sheet)

This measure guideline covers how to assess and carry out the combustion safety procedures for appliances and heating equipment that uses indoor air for combustion in low-rise residential buildings. Only appliances installed in the living space, or in an area freely communicating with the living space, vented alone or in tandem with another appliance are considered here. A separate measure guideline addresses combustion appliances located either within the living space in enclosed closets or side rooms or outside the living space in an adjacent area like an attic or garage that use outdoor air for combustion. This document is for inspectors, auditors, and technicians working in homes where energy upgrades are being conducted whether or not air infiltration control is included in the package of measures being applied. In the indoor combustion air case, guidelines summarized here are based on language provided in several of the codes to establish minimum requirements for the space using simplified prescriptive measures. In addition, building performance testing procedures are provided by testing agencies. The codes in combination with the test procedures offer comprehensive combustion safety coverage to address safety concerns, allowing inexperienced residential energy retrofit inspectors to effectively address combustion safety issues and allow energy retrofits to proceed.

32 ENERGY CONSERVATION, CONSUMPTION, AND UTILIZATI↗

DOE OSTI2014

Measure Guideline: Combustion Safety for Natural Draft Appliances Using Indoor Air

32 ENERGY CONSERVATION, CONSUMPTION, AND UTILIZATI↗

DOE OSTI2022

Low Temperature Combustion Exploration with Negative Valve Overlap

Progressively stringent emission regulations and increasing regulatory demands on fuel economy have led to advanced combustion development. Low temperature combustion (LTC), specifically homogenous charge compression ignition (HCCI), is a promising technology for reducing exhaust emissions and improving efficiency. However, its operating range is limited to low load without boosting and EGR, due to low volumetric efficiency and high pressure rise rates. In addition, effectively controlling the combustion phasing is another challenge in realizing the associated combustion gains. In this work, advanced valve control mechanisms known as continuously variable valve duration (CVVD) and continuously variable valve timing (CVVT) were used for both intake and exhaust valvetrains to enable negative valve overlap (NVO) for trapping hot exhaust residuals and to promote multipoint simultaneous ignition. Heat release phasing was controlled by varying the fueling scheme and by adjusting the amount of NVO. Parametric studies on valve timing and duration, fueling strategy, lambda, spark assist, etc., were carried out first. Afterwards the LTC strategy was proposed and then LTC operation was explored at different engine speeds. Various approaches for extending load limits were summarized and discussed. Finally, combustion performance was compared to that of spark ignition combustion, demonstrating the combustion gains of LTC.

02 PETROLEUM↗

NASA NTRS1953

Analytical evaluation of effect of equivalence ratio inlet-air temperature and combustion pressure on performance of several possible ram-jet fuels

The results of an analytical investigation of the theoretical air specific impulse performance and adiabatic combustion temperatures of several possible ram-jet fuels over a range of equivalence ratios, inlet-air temperatures, and combustion pressures, is presented herein. The fuels include octane-1, 50-percent-magnesium slurry, boron, pentaborane, diborane, hydrogen, carbon, and aluminum. Thermal effects from high combustion temperatures were found to effect considerably the combustion performance of all the fuels. An increase in combustion pressure was beneficial to air specific impulse at high combustion temperatures. The use of these theoretical data in engine operation and in the evaluation of experimental data is described.

COMBUSTION - TURBINE ENGINES↗

DOE OSTI2026

Fabrication, oxidation, and combustion of nanoscale magnesium diboride and tetraboride

The difficult ignition and low combustion efficiency of boron particles decrease the performance of boron-loaded, fuel-rich propellants for solid fuel ramjets and ducted rockets. One approach to solving this problem involves the use of magnesium diboride (MgB 2 ), which ignites easier than boron. Magnesium tetraboride (MgB 4 ) offers greater energy density owing to its higher boron content. However, the effect of B/Mg ratio on the ignition and combustion is unknown. Additionally, while nanoscale MgB₂ particles and quasi-2D structures are promising energetic additives, the oxidation and combustion properties of nanoscale MgB₄ have not been explored. To address these knowledge gaps, the present work included synthesis and high-energy ball milling of MgB 2 and MgB 4 powders, thermogravimetric analysis (TGA) of their oxidation, and combustion experiments with thin layers of the obtained powders. Comparison of two synthesis routes (a solid-state reaction in a tube furnace and combustion synthesis) has shown that the former is the superior method for producing magnesium borides. TGA has revealed that oxidation of both MgB 2 and MgB 4 results in a high conversion into the oxides (88–91 %), far exceeding the low conversion of boron (62.5 %). MgB 4 begins to oxidize rapidly at a much lower temperature (∼900 °C) than MgB 2 (∼1200 °C). The burning rates of milled MgB 2 and MgB 4 are about eight and five times, respectively, faster than that of submicron boron. Magnesium borides exhibit a stable, sustained boron flame, needed for high combustion efficiency, whereas physical Mg/B mixtures undergo Mg-driven "flash" combustion.

Boron↗

DOE OSTI2014

Characterizing dilute combustion instabilities in a multi-cylinder spark-ignited engine using symbolic analysis

Spark-ignited internal combustion engines have evolved considerably in recent years in response to increasingly stringent regulations for emissions and fuel-economy. One new advanced engine strategy utilizes high levels of exhaust gas recirculation (EGR) to reduce combustion temperatures, thereby increasing thermodynamic efficiency and reducing nitrogen oxide emissions. While this strategy can be highly effective, it also poses major control and design challenges due to the large combustion oscillations that develop at sufficiently high EGR levels. Previous research has documented that combustion instabilities can propagate between successive engine cycles in individual cylinders via self-generated feedback of reactive species and thermal energy in the retained residual exhaust gases. In this work, we use symbolic analysis to characterize multi-cylinder combustion oscillations in an experimental engine operating with external EGR. At low levels of EGR, intra-cylinder oscillations are clearly visible and appear to be associated with brief, intermittent coupling among cylinders. As EGR is increased further, a point is reached where all four cylinders lock almost completely in phase and alternate simultaneously between two distinct bi-stable combustion states. From a practical perspective, it is important to understand the causes of this phenomenon and develop diagnostics that might be applied to ameliorate its effects. We demonstrate here that two approaches for symbolizing the engine combustion measurements can provide useful probes for characterizing these instabilities.

42 ENGINEERING↗

DOE OSTI2021

Assessment of Turbulent Combustion Models for Simulating Prechamber Ignition in a Natural Gas Engine

Lean combustion is a promising strategy to increase thermal efficiency in an internal combustion engine, by exploiting a favorable specific heat ratio of the fresh mixture while simultaneously suppressing the heat losses to the cylinder wall. However, unstable ignition and slow flame propagation at fuel-lean conditions lead to large cycle-to-cycle variability and limit the high-efficiency engine operating range. Prechamber ignition is considered an effective concept to extend the lean operating limit, by providing spatially distributed ignition with multiple turbulent flame-jets and enabling a faster combustion rate compared to the conventional spark ignition approach. From a numerical modeling standpoint to date science base and available simulation tools are inadequate to properly understand and predict the combustion processes in prechamber ignited engines. In this paper, conceptually different Reynolds-averaged Navier–Stokes (RANS) combustion models widely adopted in the engine modeling community are used to simulate the ignition and combustion processes in a medium-duty natural gas engine with a prechamber spark-ignition system. Here, a flamelet-based turbulent combustion model, i.e., G-equation, and a multizone well-stirred reactor model are employed for this modeling study. Simulation results are compared with experimental data in terms of in-cylinder pressure and heat release rate. Finally, the analysis of the performance of the two models is carried out to highlight the strengths and limitations of the two evaluated approaches.

42 ENGINEERING↗

DOE OSTI2020

Assessment of turbulent combustion models for simulating pre-chamber ignition in a natural gas engine

Lean combustion in an internal combustion engine is a promising strategy to increase thermal efficiency by leveraging a more favorable specific heat ratio of the fresh mixture and simultaneously suppressing the heat losses to the cylinder wall. However, unstable ignition events and slow flame propagation at fuel-lean condition lead to high cycle-to-cycle variability and hence limit the high-efficiency engine operating range. Pre-chamber ignition is considered an effective concept to extend the lean operating limit, by providing spatially distributed ignition with multiple turbulent flame-jets and enabling faster combustion rate compared to the conventional spark ignition approach. From a numerical modeling perspective, to date, still the science base and available simulation tools are inadequate for understanding and predicting the combustion processes in pre-chamber ignited engines. In this paper, conceptually different RANS combustion models widely adopted in the engine modeling community were used to simulate the ignition and combustion processes in a medium-duty natural gas engine with a pre-chamber spark-ignition system. A flamelet-based turbulent combustion model, i.e., G-equation, and a multi-zone well-stirred reactor model were employed for the multi-dimensional study. Simulation results were compared with experimental data in terms of in-cylinder pressure and heat release rate. Finally, the analysis of the performance of the two models is carried out to highlight the strengths and limitations of the two formulations respectively.

combustion model evaluation↗

DOE OSTI2018

Flow Mechanisms and Diffusion Combustion of Turbulent Jets

The problem of flow and combustion of turbulent jets of fuel gas in the external medium of an oxidant (air) is solved with regard to the existence of the actual boundary of the turbulent flow region of a jet. Based on the ideas of the friction force of the external flow acting on the boundary of a jet, the entrainment equation for the external medium is derived that closes the system of equations of motion of turbulent jets. The physical meaning of the dissipation rate of the turbulent energy of a jet is interpreted as the work of the friction force. To describe the combustion kinetics, the limit of instantaneous reactions corresponding to the diffusion combustion mode is used. Calculations of the effective reaction rates for reactants and the volumes occupied by them are based on the representation of a turbulent medium as an aggregation of independent turbulent particles—vortices—whose random contacts lead to the mixing and combustion of reacting substances [31]. The concomitant phenomena of flow and combustion are analyzed, including radiation effects. In particular, it is shown that the apparent increase in the combustion temperature with increasing Reynolds number is in fact attributed to the relative decrease of thermal radiation losses. Qualitative agreement is obtained between the results of the theoretical calculations of the length of a combustion torch and experimental data.

42 ENGINEERING↗

DOE OSTI2018

Impact of Injection Strategies on Combustion Characteristics, Efficiency and Emissions of Gasoline Compression Ignition Operation in a Heavy-duty Multi-cylinder Engine

Gasoline compression ignition using a single gasoline-type fuel for direct/port injection has been shown as a method to achieve low-temperature combustion with low engine-out NO(x)and soot emissions and high indicated thermal efficiency. However, key technical barriers to achieving low-temperature combustion on multi-cylinder engines include the air handling system (limited amount of exhaust gas recirculation) as well as mechanical engine limitations (e.g. peak pressure rise rate). In light of these limitations, high-temperature combustion with reduced amounts of exhaust gas recirculation appears more practical. Furthermore, for high-temperature gasoline compression ignition, an effective aftertreatment system allows high thermal efficiency with low tailpipe-out emissions. In this work, experimental testing was conducted on a 12.4 L multi-cylinder heavy-duty diesel engine operating with high-temperature gasoline compression ignition combustion with port and direct injection. Additionally, engine testing was conducted at an engine speed of 1038 r/min and brake mean effective pressure of 1.4 MPa for three injection strategies, late pilot injection, early pilot injection, and port/direct fuel injection. Furthermore, the impact on engine performance and emissions with respect to varying the combustion phasing were quantified within this study. At the same combustion phasing, early pilot injection and port/direct fuel injection had an earlier start of combustion and higher maximum pressure rise rates than late pilot injection attributable to more premixed fuel from pilot or port injection; however, brake thermal efficiencies were higher with late pilot injection due to reduced heat transfer. Early pilot injection also exhibited the highest cylinder-to-cylinder variations due to differences in injector behavior as well as the spray/wall interactions affecting mixing and evaporation process. Overall, peak brake thermal efficiency of 46.1% and 46% for late pilot injection and port/direct fuel injection was achieved comparable to diesel baseline (45.9%), while early pilot injection showed the lowest brake thermal efficiency (45.3%).

42 ENGINEERING↗

DOE OSTI2019

Integrated Flue Gas Purification and Latent Heat Recovery for Pressurized Oxy-Combustion (Final Scientific/Technical Report)

Pressurized oxy-combustion has been identified by DOE as a transformational technology for coal power with carbon capture due to the advantages that are realized when the combustion process is pressurized. The staged pressurized oxy-combustion (SPOC) process is particularly attractive as the efficiency of the process is almost 6 percentage points greater than that of first generation oxy-combustion. A critical component of the SPOC process, and potentially other pressurized combustion processes, is the Direct Contact Cooler (DCC) where the latent heat of the flue gas moisture is recovery to improve plant efficiency while simultaneously removing SO x and NO x from the flue gas, so that the FGD and de-NO x processes can be eliminated, and the cost of electricity minimized. The objective of this R&D effort was to advance the TRL of the DCC technology, which included performance testing at a 100 kW scale to validate the process and obtain key engineering data for scale-up. A collateral objective was to study the gas- and liquid-phase kinetics, and the development of a systematic chemical mechanism validated by experimental data. Experiments in a bench-scale stirred reactor provided an updated understanding of the liquid chemistry and the effects of temperature and pH. This information was used to develop a reduced reaction mechanism, which was subsequently incorporated in an ASPENbased process model, to allow for evaluation of the DCC at full scale. A small-pilot DCC column was designed, constructed and tested using simulated flue gas at the pressurized oxy-combustion test facility at Washington University in St. Louis. In the majority of tests, the SO 2 capture approached 100%, making the NO x capture the primary metric of capture efficiency. An NO x capture efficiency of 90% was achieved when the gas residence time was 95 seconds, demonstrating that high capture rates can be attained with reasonable reactor size. At higher temperatures (up to 200°C inlet gas temperature) the total NO x scrubbing efficiency was reduced by approximately 10% (compared to room temp.) and this was attributed to a reduced NO oxidation rate. A significant amount of SO 2 was present in the gas outlet (10%) only when the temperature was high and the N:S ratio was low (N/S < 1), which highlights the necessity of controlling the NOx concentration in the flue gas for complete sulfur scrubbing. After incorporated our optimized chemical mechanism into an ASPEN process model, various full-scale configurations of the DCC were evaluate, and the results indicate that the proposed DCC can accomplish its intended goals at full scale and at a modest size. Thus, the results of this project indicate that the DCC is a promising technology for recovery of the latent heat of the moisture in the flue gas while simultaneously scrubbing the nitrogen and sulfur oxides, thus enabling pressurized oxy-combustion, in general, and the SPOC process, in particular.

01 COAL, LIGNITE, AND PEAT↗

DOE OSTI2020

Spatiotemporal flame propagations, combustion and solid particle emissions from lean and stoichiometric gasoline direct injection engine operation

Increased particle number and mass emissions in gasoline direct injection (GDI) engines should require to investigate in-cylinder flame and combustion characteristics associated with primary source of particle emissions. In this article, in-cylinder spatiotemporal flame luminosity is quantitatively characterized to features combustion process and solid particle emissions from a GDI engine operating in two lean and one stoichiometric modes. Low- and high-steady state operating points were used to compare combustion strategies on flame development and emission characteristics. A fiber-optic sensor composed of eight measurement channels detected the flame front and the direction of the flame propagation in the combustion chamber. Solid particle emissions in the exhaust were measured using an engine exhaust particle sizer and a micro soot sensor. Results of the experiments showed that two lean combustion modes by injection strategies resulted in distinct combustion and flame development. Lean combustion modes generated high diffusion flame by burning stratified rich-mixture. Although the lean cases resulted in strong diffusion flames, the lean-homogeneous produced similar particle size distributions with the stoichiometric mode with high ash particles. Piston pool fires on the piston surface in the lean-stratified mode induced a large accumulation mode with high particle mass concentrations.

42 ENGINEERING↗

DOE OSTI2015

Numerical and experimental studies on effects of moisture content on combustion characteristics of simulated municipal solid wastes in a fixed bed

Highlights: • The effects of moisture content on the burning process of MSW are investigated. • A two-dimensional mathematical model was built to simulate the combustion process. • Temperature distributions, process rates, gas species were measured and simulated. • The The conversion ratio of C/CO and N/NO in MSW are inverse to moisture content. - Abstract: In order to reveal the features of the combustion process in the porous bed of a waste incinerator, a two-dimensional unsteady state model and experimental study were employed to investigate the combustion process in a fixed bed of municipal solid waste (MSW) on the combustion process in a fixed bed reactor. Conservation equations of the waste bed were implemented to describe the incineration process. The gas phase turbulence was modeled using the k–ε turbulent model and the particle phase was modeled using the kinetic theory of granular flow. The rate of moisture evaporation, devolatilization rate, and char burnout was calculated according to the waste property characters. The simulation results were then compared with experimental data for different moisture content of MSW, which shows that the incineration process of waste in the fixed bed is reasonably simulated. The simulation results of solid temperature, gas species and process rate in the bed are accordant with experimental data. Due to the high moisture content of fuel, moisture evaporation consumes a vast amount of heat, and the evaporation takes up most of the combustion time (about 2/3 of the whole combustion process). The whole bed combustion process reduces greatly as MSW moisture content increases. The experimental and simulation results provide direction for design and optimization of the fixed bed of MSW.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2017

Quantum Chemical Study of Supercritical Carbon Dioxide Effects on Combustion Kinetics

In oxy-fuel combustion, the pure oxygen (O 2 ), diluted with CO 2 is used as oxidant instead air. Hence, the combustion products (CO 2 and H 2 O) are free from pollution by nitrogen oxides. Moreover, high pressures results in the near-liquid density of CO 2 at supercritical state (sCO 2 ). Unfortunately, the effects of sCO 2 on the combustion kinetics are far from being understood. In order to assist in this understanding, in this work we are using quantum chemistry methods. Here we investigate potential energy surfaces of important combustion reactions in the presence of carbon dioxide melocule. All transition states, reactant and product complexes are reported for three reactions: H 2 CO+HO 2 →HCO+H 2 O 2 (R1), 2HO 2 →H 2 O 2 +O 2 (R2), and CO+OH→CO 2 +H (R3). In the reaction R3, covalent binding of CO 2 to OH radical and then CO molecule opens a new pathway, including hydrogen transfer from oxygen to carbon atoms followed by CH bond dissociation. Compared to bimolecular OH+CO mechanism, this pathway reduces the activation barrier by 5 kcal/mol, and is expected to accelerate the reaction. This is the first report of autocatalytic effect in combustion. In case of hydroperoxyl self-reaction 2HO 2 →H 2 O 2 +O 2 the intermediates, containing covalent bonds to CO 2 were found not to be competitive. However, the spectator CO 2 molecule is able to stabilize the cyclic transition state and lower the barrier by 3 kcal/mol. Formation of covalent intermediates was also discovered in H 2 CO+HO 2 →HCO+H 2 O 2 reaction, but these specie lead to substantially higher activation barriers which makes them unlikely to play role in hydrogen transfer kinetics. The van der Waals complexation with carbon dioxide also stabilized transition state and reduces reaction barrier. Lastly, these results indicate that CO 2 environment is likely to have catalytic effect on combustion reactions, which needs to be included in kinetic combustion mechanisms in supercritical CO 2 .

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2026

Selective Chemical Looping Combustion of Terminal Alkynes in Mixtures with Alkenes

The selective combustion of terminal alkynes in mixtures with alkenes is demonstrated during anaerobic reduction half-cycles on bulk bismuth oxide (Bi 2 O 3 ) as an approach to remove alkynes, which act as inhibitors in olefin polymerization. Bi 2 O 3 combusts phenylacetylene in styrene, 3-methylphenylacetylene in 3-methylstyrene, propyne in propylene, 1-hexyne in 1-hexene, and 1-octyne in 1-octene, with alkyne combustion selectivities exceeding 96%. Near unity reaction orders for hydrocarbon consumption during reduction half-cycles are consistent with combustion pathways initiated by rate-determining initial C–H activation, which drive selective alkyne combustion through intrinsic differences in the first-order rate constants for alkyne and alkene combustion rather than preferential adsorption of alkynes on Bi 2 O 3 surfaces. Computational assessments of initial C–H activation pathways for alkynes and alkenes on (010) α-Bi 2 O 3 surfaces using density functional theory illustrate that heterolytic transition states which form proton-carbanion pairs on Bi–O sites kinetically favor the activation of alkynes rather than alkenes due to differences in C–H bond acidity, and the barrier for heterolytic C–H activation is dictated in part by the sum of the molecular deprotonation energy and the energy to bind an R – carbanion to a Bi site in its transition-state geometry. Finally, these heterolytic reactivity channels during selective chemical looping combustion present novel routes for purifying olefin gas streams containing alkyne impurities.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗