Showing papers on "Burn rate (chemistry) published in 2018"

The Effect of Fuel-Injection Timing on In-cylinder Flow and Combustion Performance in a Spark-Ignition Direct-Injection (SIDI) Engine Using Particle Image Velocimetry (PIV)

Abstract: This study applies particle image velocimetry (PIV) to an optical spark-ignition direct-injection engine in order to investigate the effects of fuel-injection on in-cylinder flow. Five injection timing combinations, each employing a stoichiometric 1:1 split ratio double-injection strategy, were analysed at an engine speed of 1200 RPM and an intake pressure of 100 kPa. Timings ranged from two injections in the intake stroke to two injections in the compression stroke, resulting in a variety of in-cylinder environments from well-mixed to highly turbulent. PIV images were acquired at a sampling frequency of 5 kHz on a selected swirl plane. The flow fields were decomposed into mean and fluctuating components via two spatial filtering approaches — one using a fixed 8 mm cut-off length, and the other using a mean flow speed scaled cut-off length which was tuned in order to match the turbulent kinetic energy (TKE) profile of a 300 Hz temporal filter. From engine performance tests, the in-cylinder pressure traces, indicated mean effective pressure (IMEP), and combustion phasing data showed very high sensitivity to injection timing variations. To explain the observed trend, correspondence between the measured flow and these performance parameters was evaluated. An expected global trend of increasing turbulence with retarded injection timing was clearly observed; however, relationships between TKE and burn rate were not as obvious as anticipated, suggesting that turbulence is not the predominant factor associated with injection timing variations which impacts engine performance. Stronger links were observed between bulk flow velocity and burn rate, particularly during the early stages of flame development. Injection timing was also found to have a significant impact on combustion stability, where it was observed that low-frequency flow fluctuation intensity revealed strong similarities with the coefficient of variance (CoV) of IMEP, suggesting that these fluctuations are a suitable measure of cycle-to-cycle variation — likely due to the influence of bulk flow on flame kernel development.

A mesoscopic numerical analysis for combustion reaction of multi-component PBX explosives

Abstract: A mesoscopic combustion reaction model of multi-component PBX explosives by using a coupled thermo-mechanical constitutive model is studied Thereinto, based on the heat balance equation, the present temperature can be calculated; the changing physical state of different materials is described by establishing different equations of state, and based on specially appointed constitutive equations, the microcracks in PBXs are described Furthermore, the concept of combustion reaction degree is established, which takes temperature as a criterion for changing physical state The model is implemented within the framework of the material point method so that the different gradient in the governing differential equations could be discretized in a single computational domain and that continuous remeshing is not required with increasing reaction time The proposed model-based simulation procedure is verified with the burn rate, the peak pressure, and temperature of PBX explosives under macroscopic scale

Sounding Rockets: analysis, simulation and optimization of a solid propellant motor using Hopsan

Abstract: The aim of the present paper is to expose the performance simulation of a small sounding rocket that operates with a solid propellant motor. In order to contribute in the understanding of solid propellant rocket engines, this work analyses the basic functioning of this type of motor and simulates its performance in the experimental rocketry field. In a solid propellant rocket, the combustion is clearly determined by the grain shape, which establishes the burning surface as a function of time. It affects directly the chamber pressure and, along with burn rate, it determines thrust. So, as well as propellant characteristics, burning surface is an essential parameter and the engineer can modify it in order to obtain the desired performance. The simplicity of the solid motor and the large number of possible grain burning shapes make solid propellants an interesting option for a rocket engine design. Therefore, the focus of this study is to build a complete model of solid combustion, with a specific burning shape, that simulates the rocket performance. The motor dimensions have been based on an Aerotech engine used in experimental rocketry. It has served as a model for the first calculations and its real performance has proved to be a good comparison tool for the results obtained. The simulation has been carried out in Hopsan, a multi-domain software developed at the Linkoping University. Once the simulation is completely built, an optimization of the engine has been done in order to improve the performance and to increase the altitude reached by the rocket. Finally, the results obtained with the optimization of the system are compared with different case dimensions. Hence, the comparison gives an idea of how this parameter affects rocket performance.

Investigations into the copper chromite particle size effect on the combustion characteristics of poly(vinyl-chloride) plastisol propellants

Abstract: The investigation of the possibility to optimize ballistic behavior and consequently to obtain better performance without affecting the cost and safety aspect of plastisol propellants has been presented in this paper. Addition of specific additives and changes in particle size can be one of these solutions, which are continuously in research. The use of burn rate modifier and metallic fuel, with finer particle sizes, becomes mandatory, to enhance the catalytic effect on ammonium perchlorate and to offer additional high heat release. Moreover, the knowledge of the combustion characteristics and especially the burning rate depending on the combustion chamber pressure of the propellant are important conditions in the validation and successful design of a solid rocket motor. The first part of this work deals with the selection of the higher energetic catalyst among three of the most common of them, namely copper chromite, ferric oxide and ferrocene. The selection results in choosing copper chromite as the best burning catalyst. Then, we have studied the effect of its particle size on the thermoanalytical properties of poly(vinyl-chloride) plasticized propellants, by the determination of energetic and kinetic characteristics through the use of an adiabatic bomb calorimeter and a differential scanning calorimeter respectively. The kinetic parameters were determined by Ozawa and Kissinger methods and compared. Besides, the effect of particle size on the combustion properties has been also studied. The plot of the burning rate-pressure curves is used to determine the combustion laws using a strand burner in the typical Crawford bomb. Copper chromite and its particle size have been found to influence the decomposition and to enhance the burning rate of the plastisol propellants. In the second part, we have investigated the energetic effect of fine aluminum powder on the thermal decomposition of ammonium perchlorate and of plastisol propellant as a function of its concentration, both in the presence and the absence of 1 mass-% copper chromite in the basic propellant composition. Aluminum is chosen because of its effect to get high flame temperatures and increased performance.