Calculated Heat Release Research Articles

Evaluation of heat release indicators in lean premixed H2/Air cellular tubular flames

Heat release rate in combustion systems must be understood in order to control thermoacoustic instabilities, flame extinction, and heat losses. Traditionally OH chemiluminescence (OH*) is used to trace heat release rate (HRR) in H2/air flames, but its accuracy as a tracer has not been assessed. Lean premixed H2/air cellular tubular flames are a good test case to evaluate HRR tracers due to the presence of highly reactive flame cells surrounded by regions of near extinction. Comparing the calculated heat release rate to OH* concentration, one finds that [OH*] profiles correlate with the regions of high reactivity (flame cells) but the correlation fails in the low reactivity regions where the HRR is much higher than the [OH*] value indicates. Alternate HRR tracers including [H] and pixel-by-pixel products of [O2]x[H], [OH]x[H2], and [O]x[H2] are analyzed with detailed numerical simulations. The chosen products derive from the main chain reaction steps that contribute to overall HRR in lean, premixed H2/air flames. Findings suggest that [H] is an accurate yet simple way of tracking HRR. Planar measurements of HRR are possible if LIF measurements of [H] are improved.

Potential of Real-Time Cylinder Pressure Analysis by Using Field Programmable Gate Arrays

In this paper, a Field Programmable Gate Array (FPGA) was used to implement a real-time cylinder pressure analysis. The goal of the project was to improve the accuracy of calculated heat release and center of combustion calculations to enhance the precision of engine control functions. Compared to today’s real-time pressure analysis systems, several additional physical effects were taken into account for this objective. The wall heat transfer was calculated based on the approach published by Hohenberg. A chemical equilibrium with six substances was assumed for the mixture composition and a real-time calculation method was developed. Furthermore, a two-zone model was adapted and implemented for this realtime analysis. The validation of the results and the rating of the improvement in precision were based on GT-SUITE simulation results as an offline reference tool. Compared to state-of-the-art analysis systems, it was possible to reduce the average error of the center of combustion position from 1.6° to 0.5° crank angle (CA) by taking the investigated effects into account. Moreover, it was possible to significantly reduce the time required for the calculation from one complete combustion cycle to 0.2°CA at an engine speed of 3,000 rpm by using a continuous calculation method on the FPGA. This led to an additional improvement of the ability to control the engine, especially under highly dynamic operation conditions.

Cylinder Pressure-Based Virtual Sensor for In-Cycle Pilot Mass Estimation

In this paper, a virtual sensor for the estimation of the injected pilot mass in-cycle is proposed. The method provides an early estimation of the pilot mass before its combustion is finished. Furthermore, the virtual sensor can also estimate pilot masses when its combustion is incomplete. The pilot mass estimation is conducted by comparing the calculated heat release from in-cylinder pressure measurements to a model of the vaporization delay, ignition delay and the combustion dynamics. A new statistical approach is proposed for the detection of the start of vaporization and the start of combustion. The discrete estimations, obtained at the start of vaporization and the start of combustion, are optimally combined and integrated in a Kalman Filter that estimates the pilot mass during the vaporization and combustion. The virtual sensor was programmed in a Field Programmable Gate Array (FPGA), and its performance tested in a Scania D13 Diesel engine. The experimental results showed that the method can effectively improve the in-cycle pilot mass estimation. The accuracy, quantified by the average error between the actual injected mass and the estimated mass, was improved from an induced initial bias error of ±3 mg/st to a final error of ±0.1 mg/st, with a precision of ±0.45 mg/st. A level of precision of ±0.5 mg/st was already obtained at the peak of the pilot heat release. The suggested method is robust against changing operating conditions based on the calibration points. With the proposed parametrization, this is limited to regions where the parameter dependence is linear. The maximum calibration bias error for points out of the calibration range was within ±0.5 mg/st, with a precision of ±0.8 mg/st. In addition, the method was found to be robust against most input measurement errors and parameter bias. The major error sensitivity was detected for TDC offset. Different fuels than those used for calibration were found to result in an error proportional to the lower heating value error. The estimation framework can easily integrate more complex models to allow the estimation of greater pilot masses and multiple injections. The pilot mass estimation can be used to predict the pilot combustion and its effect on the main injection. This allows for better in-cycle controllability i.e. ability to adjust the main injection timing and duration, cycle-to-cycle control and adaptation of pilot and main injections. The closed-loop control of the combustion enables improved engine performance and efficiency, and reduced emissions variability. (Less)

Internal combustion engine heat release calculation using single-zone and CFD 3D numerical models

The present study deals with a comparative evaluation of a single-zone (SZ) thermodynamic model and a 3D computational fluid dynamics (CFD) model for heat release calculation in internal combustion engines. The first law, SZ, model is based on the first law of thermodynamics. This model is characterized by a very simplified modeling of the combustion phenomenon allowing for a great simplicity in the mathematical formulation and very low computational time. The CFD 3D models, instead, are able to solve the chemistry of the combustion process, the interaction between turbulence and flame propagation, the heat exchange with walls and the dissociation and re-association of chemical species. They provide a high spatial resolution of the combustion chamber as well. Nevertheless, the computation requirements of CFD models are enormously larger than the SZ techniques. However, the SZ model needs accurate experimental in-cylinder pressure data for initializing the heat release calculation. Therefore, the main objective of an SZ model is to evaluate the heat release, which is very difficult to measure in experiments, starting from the knowledge of the in-cylinder pressure data. Nevertheless, the great simplicity of the SZ numerical formulation has a margin of uncertainty which cannot be known a priori. The objective of this paper was, therefore, to evaluate the level of accuracy and reliability of the SZ model comparing the results with those obtained with a CFD 3D model. The CFD model was developed and validated using cooperative fuel research (CFR) engine experimental in-cylinder pressure data. The CFR engine was fueled with 2,2,4-trimethylpentane, at a rotational speed of 600 r/min, an equivalence ratio equal to 1 and a volumetric compression ratio of 5.8. The analysis demonstrates that, considering the simplicity and speed of the SZ model, the heat release calculation is sufficiently accurate and thus can be used for a first investigation of the combustion process.

Experimental Study of the Polytropic Coefficient for an Air-Cooled, High-Compression-Ratio, Spark-Ignition Engine Fueled with Natural Gas, Biogas, and a Propane–Syngas Blend

The polytropic coefficient is an important variable for determining errors in pressure and volume measurements and for apparent heat release calculation in engine combustion analysis. For commercial gasoline-fueled spark ignition engines and diesel-fueled compression ignition engines exist a wide understanding about the thermodynamic models and values of polytropic coefficient, however, in other technologies, in which gaseous fuels are used, the pressure treatment strategies and heat transfer models should be adjusted to allow a better calculation of polytropic coefficient. This paper presents a study on the effects of fuel composition, spark timing, and engine load on polytropic coefficient determination in an air cooled spark ignition engine with high compression ratio (15.5:1), which it was fueled with natural gas, biogas, and propane-syngas blend. The experimental results suggests that during compression an appropriate crank angle interval for polytropic coefficient estimation is between 50 and 30 cra...

B-35 東京23区のエネルギー消費に伴う熱代謝構造に関する研究 : その1 人工排熱の算出

B-35 東京23区のエネルギー消費に伴う熱代謝構造に関する研究 : その1 人工排熱の算出

High spatial- and temporal-resolution anthropogenic heat discharge estimation in Los Angeles County, California

Anthropogenic heat flux (Qf), which originates through energy consumption from buildings, industrial plants, vehicle exhausts, and human metabolism releases, is an important component in the urban Surface Energy Balance (SEB) system, and is key to understanding of many urban environmental issues. The present study provided a hybrid Qf modeling approach, which combined the inventory and GIS approach to create a 365-day hourly Qf profile at 120 m spatial resolution in Los Angeles County, California, USA. Qf was estimated by separate calculation of heat release from buildings, traffics, and human metabolism, respectively. The results indicated that Qf showed different magnitudes and diurnal patterns between workdays (dual-peak shape) and weekends/holidays, and also varied with seasons, and land use types. Qf yielded the highest values in the summer workdays, with its maximum value of 7.76 w/m2. Qf in hot summer workdays was obviously higher than that in the average summer workdays, which caused by higher demands for space cooling in buildings, and can reach 8.14 w/m2 at maximum. Building energy consumption was identified as the dominant contributor to the Qf in Downtown Los Angeles, which was found to have the largest mean Qf throughout the year among all neighborhoods. It can be concluded that Qf in the downtown was more significant in workdays than that in non-workdays, and its maximum value can reach 100 w/m2. It is suggested that our approach may have wider applicability for Qf estimation in large areas compared with the existing studies, as all the data used were available to the public. A high spatial and temporal Qf profile, which can readily be incorporated into urban energy balance and Urban Heat Island (UHI) studies, provides valuable data and information for pertinent government agencies and researchers.

Characterization of a mine fire using atmospheric monitoring system sensor data.

Atmospheric monitoring systems (AMS) have been widely used in underground coal mines in the United States for the detection of fire in the belt entry and the monitoring of other ventilation-related parameters such as airflow velocity and methane concentration in specific mine locations. In addition to an AMS being able to detect a mine fire, the AMS data have the potential to provide fire characteristic information such as fire growth - in terms of heat release rate - and exact fire location. Such information is critical in making decisions regarding fire-fighting strategies, underground personnel evacuation and optimal escape routes. In this study, a methodology was developed to calculate the fire heat release rate using AMS sensor data for carbon monoxide concentration, carbon dioxide concentration and airflow velocity based on the theory of heat and species transfer in ventilation airflow. Full-scale mine fire experiments were then conducted in the Pittsburgh Mining Research Division's Safety Research Coal Mine using an AMS with different fire sources. Sensor data collected from the experiments were used to calculate the heat release rates of the fires using this methodology. The calculated heat release rate was compared with the value determined from the mass loss rate of the combustible material using a digital load cell. The experimental results show that the heat release rate of a mine fire can be calculated using AMS sensor data with reasonable accuracy.

Heat Release Calculation of Internal Combustion Engines by Analyzing the Flame Radiation with Crankshaft Angle Resolution

Improving efficiency and reducing emissions are the principal challenges in developing new generations of internal combustion engines. Different strategies such as downsizing or sophisticated after-treatment of exhaust gases are pursued.Another approach aims at optimizing the parameterization of the engine. Correct adjustments of ignition timings, waste gate position and other factors have significant influence on the combustion process. A multitude of application data is generated during the development process to predefine appropriate settings for most situations. Improvements in regards to the application effort and the quality of the settings can be achieved by measuring the combustion process and optimizing the parametrization in a closed loop. However, cylinder pressure sensors that are used during the development process are too expensive for series applications.This paper focuses on an affordable combustion sensor based on the measurement of the electromagnetic radiation of the combustion flame.The intensity of electromagnetic radiation by chemiluminescence is a good indicator for the status of the combustion as it is primarily dependent on the number of excited molecules. A characteristic spectral band is emitted by the OH radical, which is created in the flame front and corresponds to the number of reactants that are burned.A research engine was equipped with an access for an optical measurement system for chemiluminescence and light emission in general. To achieve sufficient amplification and temporal bandwidth, a special detector circuitry was designed.The measurement data was used to analyze the quality of different light emission signals and to investigate their qualification for heat release calculations.

A method to calculate wall heat fluxes of electrical equipments based on overdetermined linear equation

Cooling load of air-conditioning systems in underground space mainly refersto heat released from multitudinous electrical equipments. Calculation of the total amount of heat release is of great importance to the underground ventilation and air conditioning systems during design stage for indoorthermalenvironment. A method based on overdetermined linear equation is applied to calculate heat release fluxes of equipment surfaces in an underground space. Firstly, a field test in an underground hydropower station was carried out. Temperatures of electrical equipment surfaces, walls, underground indoor air and dimensions of electrical equipments were obtained. Conventional methods based on heat transfer theory can obtain the results with a standard error of 0.59, which is a relatively high value. On basis of overdetermined linear equation, the method combines on-site temperature measurements with numerical simulation to calculate wall heat fluxes. When seven testing points are selected in the on-site temperature measurements for calculation, the heat release fluxes of three equipment surfaces can be obtained with a standard error of 0.07. The method based on overdetermined linear equation is an effective way to determine wall heat fluxes of electrical equipments in air conditioned space.

The Process of Batch Combustion of Logs in Wood Stoves - Transient Modelling for Generation of Input to CFD Modelling of Stoves and Thermal Comfort Simulations

CFD modelling of wood stoves are a challenge due to the transient behavior of the combustion process, due to their batch combustion principle. Various initial and boundary conditions needs to be specified to carry out a CFD simulation of a wood stove, and many of these will be a result of sub-models that again can be partly based on experimental results. This paper deals with these boundary conditions and the generation of representative values for these as input to stationary and transient CFD simulations throughout the batch combustion process as well as thermal comfort simulations. Additionally, heat production profiles and stove wall properties are needed to calculate heat release profiles to the room in which the stove is placed. These heat release profiles are essential input for evaluating the thermal comfort of wood stoves in houses, a subject which has received considerable attention recently as energy efficient houses are increasingly introduced. Necessary boundary conditions relates to the fuel and air introduction into the computational domain and the thermal and radiative properties of the surfaces within and enclosing the computational domain. In addition initial conditions must be specified as starting point for the transient models generating the boundary conditions at any time in the batch combustion process. The ultimate goal would be to carry out transient CFD simulations where the boundary conditions are derived for each new stationary simulation based on the results from the previous time step. The choice of models and the degree of detail of these regarding e.g. the handling of the gas phase chemistry are very important. In this paper a feasible modelling approach is presented that together with experiments could be used to cost-efficiently design future's high performance wood stoves.

An analytical model to predict nitric oxide concentration in a diesel engine for potential use as feedback for model-based engine control

Governmental regulation of harmful pollutants requires reduced in–cylinder nitric oxide (NO) formation in internal combustion engines, including diesel engines. Because of the importance of NO emission, it might be desired to have a means to predict its in–cylinder concentration on a real–time basis for various applications, including engine control. Proper estimation of NO concentration during the diesel combustion process, however, is challenging due to the heterogeneous nature of the combustion mixture. For example, use of the ubiquitous single–zone model (typically used to calculate heat release during combustion) renders unrealistic mixture temperatures below those of NO formation kinetics; thus, use of the single–zone model will predict substantially lower NO concentrations than the engine's actual NO concentrations. In many cases, the single–zone model would predict zero concentrations of NO. This study renews a 'two–stage' model that computationally divides the cylinder into four zones; these four zones collectively create more realistic temperatures for the purpose of predicting in–cylinder NO concentration. This article re–introduces the two–stage model and demonstrates its effectiveness at predicting in–cylinder NO concentration.

Analysis of methodologies for calculating the heat release rates of mining vehicle fires in underground mines

Four different methodologies for calculating the ignition of different components on a mining vehicle in a mine drift were analysed. The results were compared with two full-scale fire experiments on mining vehicles. The four different methods are based on physical relations for fire spread between combustible components of the mining vehicles. The first two methods use a critical heat flux as ignition criterion while the other two methods use an ignition temperature. A sensitivity analysis was performed and the most influencing parameter of the methods was further analyzed. The calculated results were compared with the measured results from the experiments. The two methodologies applying an ignition temperature criterion were ruled out at as the surface temperatures of all fuel components never achieved the corresponding ignition temperatures. For the two methods applying a critical heat flux criterion it was found that the expression not including a flame radiation term was not suitable as it was found that the flame radiation played an important part with respect to spread mechanisms. The expression containing a flame radiation term was found to come very close to the observed ignition times, except in the case of the left, rear tyre of the drilling rig where it predicted a much higher ignition time than the one observed. The difference is unclear and would have to be investigated further. It was also found that the surface heat losses had none effect on the output results and could therefore be neglected in the calculations. In the case of the wheel loader the calculated heat release rate curves did not match the measured curve as well as in the case of the drilling rig. The difficulty in this case consists of accurately predicting the mechanical failure of a component – in this case a suction hose – that would initiate the very significant hydraulic oil pool fire.

Glow-plug-assisted combustion of nitromethane sprays in a constant volume chamber

Experimental investigations on spray combustion of nitromethane in air within a constant volume chamber are presented. The sprays produced by a commercial gasoline injector, were ignited by using a pair of glow plugs, while the initial chamber pressure was varied from 1 bar to 7 bar. The nature of the combustion processes at various initial pressures was elucidated by measuring the pressure rise as well as using FTIR spectroscopy of the combustion products, and high speed photography. The maximum differential pressures reached during combustion were found to increase with chamber pressure up to 4 bar, and decrease thereafter while the ignition delays were found to be in the order of 10 ms for all pressures. The global equivalence ratio was found to vary from 0.43 at an initial pressure of 1 bar to 0.06 at an initial pressure of 7 bar, thus reducing the flame temperatures achieved within the chamber with increasing chamber pressures. The trends observed in the calculated heat release rates, cumulative heat released, and rate of heat loss from the chamber were found to provide key insights into the combustion process, which was concluded to be occurring through three distinct processes – turbulent premixed combustion, turbulent spray combustion, and turbulent film combustion. The effects of decreasing flame temperatures on the three processes were discussed in detail.

Analysis of Incylinder Pressure and Temperature Variation in a Four-Stroke S. I. Engine Using Wiebe’s Combustion Model

This paper presents the modeling of in-cylinder pressure variation of a four-stroke single cylinder spark ignition engine. It uses instantaneous properties of working fluid, viz., gasoline to calculate heat release rates, needed to quantify combustion development. Cylinder pressure variation with respect to either volume or crank angle gives valuable information about the combustion process. The analysis of the pressure – volume or pressure-theta data of a engine cycle is a classical tool for engine studies. This paper aims at demonstrating the modeling of pressure variation as a function of crank angle as well as volume with the help of MATLAB program developed for this purpose. Towards this end, Woschni heat release model is used for the combustion process. The important parameter, viz., peak pressure for different compression ratios are used in the analysis. Predicted results are compared with experimental values obtained for a typical compression ratio of 8.3.

Further Development and Application of a Model for the Calculation of Heat Release in Direct Injection Diesel Engines

Further Development and Application of a Model for the Calculation of Heat Release in Direct Injection Diesel Engines

Determination of specific heat ratio and error analysis for engine heat release calculations

The burnt fraction f of Wiebe equation has been shown to be dependent only on the newly defined parameter ‘combustion burn factor (Ci)’; and the benefits of expressing heat release rate with respect to Ci have been presented. The errors associated with the determination of apparent heat release rate (Ahrr) and the cumulative heat release (Cum.Hrr) from the measured cylinder pressure data and the assumed specific heat ratio (γ) was determined and compared. The γ affected the calculated Ahrr more than the cylinder pressure. Overestimation of γ resulted in an underestimation of the peak value of the Ahrr and vice versa, this occurred without any shift in the combustion phasing. A new methodology has been proposed to determine the instantaneously and mean value of γ for a given combustion. This new methodology has been applied to determine γ for a wide range of engine operating conditions and for different fuels.

Fire scene reconstruction of a furnished compartment room in a house fire

Computational fluid dynamics (CFD) has been employed to reconstruct the burning of solid combustible materials of a house fire in Parkes, New South Wales, Australia. Experiment was conducted in a compartment room containing multiple combustible materials with an identified ignition source. Large scale fire development involving the spread of flame and smoke leading to the untenable condition of flashover was observed from on-site visualisations as well as comparison to calculated heat release rates. Significant transient fire events taken from experimental footages including the spread of flame on furniture such as couch and carpet were captured through the numerical model. The present simulation and experimental studies are currently being utilised as components for online fire training program for fire-fighters.

Heat release rate measurements of burning mining vehicles in an underground mine

Heat release rates from two full-scale fire experiments with mining vehicles in an underground mine are presented. The mining vehicles involved were a wheel loader and a drilling rig typical for mining operations. The calculated peak heat release rate of the loader was 15.9MW and occurred after approximately 11min from ignition. The calculated peak heat release rate of the drilling rig was 29.4MW and occurred after approximately 21min from ignition. The heat release rate was calculated from measured data of gas concentrations of oxygen, carbon monoxide and carbon dioxide, measured gas velocity and measured gas temperatures. The fuel load of the wheel loader consisted mainly of the tyres, the hydraulic oil and the diesel fuel. The fuel load of the drilling rig consisted mainly of the hydraulic oil and the hydraulic hoses. The calculated heat release rate curves were controlled by comparing the summed up energy contents of the participating components with the integrated heat release rate curves.

Calibration of flow rate in cone calorimeter tests

ABSTRACTThe cone calorimeter is one of the major fire tests. The measurement method is based on the evaluation of mass flow and oxygen concentration of fire effluents to calculate heat release rate. Different studies highlighted that the governing parameter for uncertainty at important values of heat release rate was the characteristic constant of an orifice plate used to measure mass flow (C‐factor). This parameter is usually determined each testing day by oxygen consumption calorimetry with a reference methane burner. This publication presents a calibration method for volumetric flow rate without using orifice plate and then an extension to C‐factor determination without methane burner and calorimetry. The uncertainty calculation applied to a real example highlights the fact that the method is suitable to respect tolerance of standardized test conditions for both parameters. Copyright © 2013 John Wiley & Sons, Ltd.