Modeling End-Gas Knock in a Rapid-Compression Machine PDF Download
Are you looking for read ebook online? Search for your book and save it on your Kindle device, PC, phones or tablets. Download Modeling End-Gas Knock in a Rapid-Compression Machine PDF full book. Access full book title Modeling End-Gas Knock in a Rapid-Compression Machine by W. B. Bush. Download full books in PDF and EPUB format.
Author: W. B. Bush Publisher: ISBN: Category : Languages : en Pages : 15
Book Description
A rapid-compression machine is a laboratory apparatus to study aspects of the compression stroke, combustion event, and expansion stroke of an Otto cycle. As a simple model of such a machine, unsteady one-dimensional nonisobaric laminar flame propagation through a combustible premixture, enclosed in a variable volume, is examined in the asymptotic limit of Arrhenius activation temperature large relative to the conventional adiabatic flame temperature. In this limit, a thin propagating flame separates nondiffusive expanses of burned and unburned gas. The pressure through the enclosure is spatially homogeneous for smooth flame propagation. However, expansion of the hot burned gas results in compressional preheating of the remaining unburned gas, and in fact the spatially homogeneous gas may undergo autoconversion prior to arrival of the propagation flame. If such an explosion is too rapid for acoustic adjustment, large spatial differences in pressure arise and the resulting nonlinear waves produce audible knock. Here attention is concentrated on what fraction (if any) of the total charge may undergo autoconversion for a given operating condition, and what enhanced heat transfer from the end gas would preclude autoconversion--though too great heat transfer from the end gas could result in flame quenching (unburned residual fuel). (Author).
Author: W. B. Bush Publisher: ISBN: Category : Languages : en Pages : 15
Book Description
A rapid-compression machine is a laboratory apparatus to study aspects of the compression stroke, combustion event, and expansion stroke of an Otto cycle. As a simple model of such a machine, unsteady one-dimensional nonisobaric laminar flame propagation through a combustible premixture, enclosed in a variable volume, is examined in the asymptotic limit of Arrhenius activation temperature large relative to the conventional adiabatic flame temperature. In this limit, a thin propagating flame separates nondiffusive expanses of burned and unburned gas. The pressure through the enclosure is spatially homogeneous for smooth flame propagation. However, expansion of the hot burned gas results in compressional preheating of the remaining unburned gas, and in fact the spatially homogeneous gas may undergo autoconversion prior to arrival of the propagation flame. If such an explosion is too rapid for acoustic adjustment, large spatial differences in pressure arise and the resulting nonlinear waves produce audible knock. Here attention is concentrated on what fraction (if any) of the total charge may undergo autoconversion for a given operating condition, and what enhanced heat transfer from the end gas would preclude autoconversion--though too great heat transfer from the end gas could result in flame quenching (unburned residual fuel). (Author).
Author: Publisher: ISBN: Category : Languages : en Pages :
Book Description
Previously we have reported on the combustion behavior of all nine isomers of heptane in a rapid compression machine (RCM) with stoichiometric fuel and ''air'' mixtures at a compressed gas pressure of 15 atm. The dependence of autoignition delay times on molecular structure was illustrated. Here, we report some additional experimental work that was performed in order to address unusual results regarding significant differences in the ignition delay times recorded at the same fuel and oxygen composition, but with different fractions of nitrogen and argon diluent gases. Moreover, we have begun to simulate these experiments with detailed chemical kinetic mechanisms. These mechanisms are based on previous studies of other alkane molecules, in particular, n-heptane and iso-octane. We have focused our attention on n-heptane in order to systematically redevelop the chemistry and thermochemistry for this C-- isomer with the intention of extending our greater knowledge gained to the other eight isomers. The addition of new reaction types, that were not included previously, has had a significant impact on the simulations, particularly at low temperatures.
Author: Publisher: ISBN: Category : Languages : en Pages : 14
Book Description
The use of gasoline in homogeneous charge compression ignition engines (HCCI) and in duel fuel diesel - gasoline engines, has increased the need to understand its compression ignition processes under engine-like conditions. These processes need to be studied under well-controlled conditions in order to quantify low temperature heat release and to provide fundamental validation data for chemical kinetic models. With this in mind, an experimental campaign has been undertaken in a rapid compression machine (RCM) to measure the ignition of gasoline mixtures over a wide range of compression temperatures and for different compression pressures. By measuring the pressure history during ignition, information on the first stage ignition (when observed) and second stage ignition are captured along with information on the phasing of the heat release. Heat release processes during ignition are important because gasoline is known to exhibit low temperature heat release, intermediate temperature heat release and high temperature heat release. In an HCCI engine, the occurrence of low-temperature and intermediate-temperature heat release can be exploited to obtain higher load operation and has become a topic of much interest for engine researchers. Consequently, it is important to understand these processes under well-controlled conditions. A four-component gasoline surrogate model (including n-heptane, iso-octane, toluene, and 2-pentene) has been developed to simulate real gasolines. An appropriate surrogate mixture of the four components has been developed to simulate the specific gasoline used in the RCM experiments. This chemical kinetic surrogate model was then used to simulate the RCM experimental results for real gasoline. The experimental and modeling results covered ultra-lean to stoichiometric mixtures, compressed temperatures of 640-950 K, and compression pressures of 20 and 40 bar. The agreement between the experiments and model is encouraging in terms of first-stage (when observed) and second-stage ignition delay times and of heat release rate. The experimental and computational results are used to gain insight into low and intermediate temperature processes during gasoline ignition.
Author: Publisher: ISBN: Category : Languages : en Pages :
Book Description
A computer model is used to examine oxidation of hydrocarbon fuels in a rapid compression machine. For one of the fuels studied, n-heptane, significant fuel consumption is computed to take place during the compression stroke under some operating conditions, while for the less reactive n-pentane, no appreciable fuel consumption occurs until after the end of compression. The third fuel studied, a 60 PRF mixture of iso-octane and n-heptane, exhibits behavior that is intermediate between that of n-heptane and n-pentane. The model results indicate that computational studies of rapid compression machine ignition must consider fuel reaction during compression in order to achieve satisfactory agreement between computed and experimental results.
Author: Colin Banyon Publisher: ISBN: Category : Combustion engineering Languages : en Pages :
Book Description
Rapid compression machines (RCMs) are well characterized laboratory scale devices capable of achieving internal combustion (IC) engine relevant thermodynamic environments. These machines are often used to collect ignition delay times as targets for gas-phase chemical kinetic fuel autoigntion models. Modern RCMs utilize creviced piston(s) to improve charge homogeneity and allow for an adequate validation of detailed chemistry mechanisms against experiments using computationally efficient, homogeneous reactor models (HRMs). Conventionally, experiments are preformed by introducing a premixed gas of fuel + oxidizer + diluent into the machine, which is compressed volumetrically via a piston. Experiments investigating low-vapor pressure fuels (e.g. diesels, biodiesels, jet fuels, etc.) and surrogates can be conducted by preheating both the charge as well as the machine. This method of fuel loading can lead to pretest fuel pyrolysis as well as machine seal degradation. Under some conditions loading a fuel aerosol of finely atomized liquid droplets in an oxidizer + diluent bath gas (i.e. wet compression) has been suggested to extend the capabilities of RCM experiments to involatile fuels. This work investigates phase-change effects during RCM experiments, especially for aerosol-fueling conditions, while the methodology can be applied to gas-phase fuel experiments where fuel condensation can occur at the compressed conditions within the boundary layer region. To facilitate this study a reduced-order, physics-based model is used. This work highlights important machine-scale influences not investigated in previous work, and provides additional detail concerning an aerosol RCM{u2019}s capabilities and limitations. A transient formulation is developed for the multi-phase transport within the RCM reaction chamber as well as the flow to the piston crevice region during both the compression and delay periods. The goal of this work is threefold. First, an a priori knowledge of the stratification present under various conditions can help determine an optimum machine geometry so that discrepancies between experimental data sets and 0D kinetics simulations are minimized for involatile fuels. Second, the model is computationally tractable to prescribe heat loss rates to an HRM during simulations of experiments so that physical effects can be incorporated into simulations using detailed chemistry. Finally, heat loss rates that are prescribed to the HRM are only a function of machine geometry, and are independent of ad hoc and empirically derived fits that vary between facilities. Thus a more adequate comparison of data between RCM facilities and with existing literature can be made.
Author: W. B. Bush
Author: W. B. Bush
Author: U. Bielert
Author: 
Author: Casey M. Allen
Author: 
Author: W. J. Pitz
Author: 
Author: Ferran Alberto Ayala
Author: Daeyup Lee
Author: Colin Banyon