Simulations of the SCHOLAR scramjet experiment

The DDES method is employed to investigate the complex physics involved in supersonic combustion and in particular in the SCHOLAR scramjet test case. The influence on computational results of prescribing turbulent fluctuations at the entrance to the combustion chamber is investigated. The interaction of shock waves, vortices, turbulence and combustion is studied and the existence of secondary vortices on the upper will of the combustor is proposed. © 2012 by Peter Cocks.

Content-Based Search Engines for Construction Image Databases

Images represent a valuable source of information for the construction industry. Due to technological advancements in digital imaging, the increasing use of digital cameras is leading to an ever-increasing volume of images being stored in construction image databases and thus makes it hard for engineers to retrieve useful information from them. Content-Based Search Engines are tools that utilize the rich image content and apply pattern recognition methods in order to retrieve similar images. In this paper, we illustrate several project management tasks and show how Content-Based Search Engines can facilitate automatic retrieval, and indexing of construction images in image databases.

A numerical simulation of AFR switch of SI engines

A novel mechanical method of achieving a rapid switch between stoichiometric and lean conditions for SI engines is explored. Two and three throttle configurations, a switch strategy which employs a standard intake manifold and an assembly of pipes and throttle(s), are investigated numerically by using a one-dimensional engine simulation program based on the method of characteristics. The results indicate that it is possible to achieve rapid AFR switch without a torque jump, i.e. unperceptible to the driver. © 1998 Society of Automotive Engineers, Inc.

Pressure data analysis of formula one racing engines

The measured time-history of the cylinder pressure is the principal diagnostic in the analysis of processes within the combustion chamber. This paper defines, implements and tests a pressure analysis algorithm for a Formula One racing engine in MATLAB1. Evaluation of the software on real data is presented. The sensitivity of the model to the variability of burn parameter estimates is also discussed. Copyright © 1997 Society of Automotive Engineers, Inc.

On the time delay in continuous in-cylinder sampling from IC engines

When gas sample is continuously drawn from the cylinder of an internal combustion engine, the sample that appears at the end of the sampling system corresponds to the in-cylinder content sometime ago because of the finite transit time which is a function of the cylinder pressure history. This variable delay causes a dispersion of the sample signal and makes the interpretation of the signal difficult An unsteady flow analysis of a typical sampling system was carried out for selected engine loads and speeds. For typical engine operation, a window in which the delay is approximately constant may be found. This window gets smaller with increase in engine speed, with decrease in load, and with the increase in exit pressure of the sampling system.

Investigation of the dilution process for measurement of particulate matter from spark-ignition engines

Measurements of particulate matter (PM) from spark ignition (SI) engine exhaust using dilution tunnels will become more prevalent as emission standards are tightened. Hence, a study of the dilution process was undertaken in order to understand how various dilution related parameters affect the accuracy with which PM sizes and concentrations can be determined. A SI and a compression ignition (CI) engine were separately used to examine parameters of the dilution process; the present work discusses the results in the context of SI exhaust dilution. A Scanning Mobility Particle Sizer (SMPS) was used to measure the size distribution, number density, and volume fraction of PM. Temperature measurements in the exhaust pipe and dilution tunnel reveal the degree of mixing between exhaust and dilution air, the effect of flowrate on heat transfer from undiluted and diluted exhaust to the environment, and the minimum permissible dilution ratio for a maximum sample temperature of 52°C. Measurements of PM concentrations as a function of dilution ratio show the competing effects of temperature and particle/vapor concentrations on particle growth dynamics, which result in a range of dilution ratios-from 13 to 18-where the effect of dilution ratio, independent of flowrate, is kept to a minimum. This range of dilution ratios is therefore optimal in order to achieve repeatable PM concentration measurements. Particle dynamics during transit through the tunnel operating at the optimal dilution ratio was found statistically insignificant compared to data scatter. Such small differences in number concentration may be qualitatively representative of particle losses for SI exhaust, but small increases in PM volume fraction during transit through the tunnel may significantly underestimate accretion of mass due to unburned hydrocarbons (HCs) emitted by SI engines. The fraction of SI-derived PM mass due to adsorbed/absorbed vapor, estimated from these data, is consistent with previous chemical analyses of PM. © 1998 Society of Automotive Engineers, Inc.

Numerical simulation of post-flame oxidation of hydrocarbons in spark ignition engines

About 50-90 percent of the hydrocarbons that escape combustion during flame passage in spark-ignition engine operation are oxidized in the cylinder before leaving the system. The process involves the transport of unreacted fuel from cold walls towards the hotter burned gas regions and subsequent reaction. In order to understand controlling factors in the process, a transient one-dimensional reactive-diffusive model has been formulated for simulating the oxidation processes taking place in the reactive layer between hot burned gases and cold unreacted air/fuel mixture, with initial and boundary conditions provided by the emergence of hydrocarbons from the piston top land crevice. Energy and species conservation equations are solved for the entire process, using a detailed chemical kinetic mechanism for propane. Simulation results show that the post-flame oxidation process takes place within a reactive layer where intermediate hydrocarbon products are formed at temperatures above 1100-1200 K, followed by a carbon monoxide conversion region closer to the hot burned gases. Model results show that most of hydrocarbons leaving the crevice are completely oxidized inside the cylinder. The largest contribution of remaining hydrocarbons are those leaving the crevice at temperatures below 1400 K. The largest fraction of non-fuel (intermediate) hydrocarbons results from hydrocarbons leaving the crevice when core temperatures are around 1400 K Copyright © 1997 Society of Automotive Engineers, Inc.

Extent of oxidation of hydrocarbons desorbing from the lubricant oil layer in spark-ignition engines

The extent of oxidation of hydrocarbons desorbing from the oil layer has been measured directly in a hydrogen-fueled, spark-ignited engine in which the lubricant oil was doped with a single component hydrocarbon. The amount of hydrocarbon desorbed and oxidized could be measured simultaneously as the dopant was only source of carbon-containing species. The fraction oxidized was strongly dependent on engine load, hydrogen fuel-air ratio and dopant chemical reactivity, but only modestly dependent on spark timing and nitrogen dilution levels below 20 percent. Fast FID measurements at the cylinder exit showed that the surviving hydrocarbons emerge late in the exhaust stroke. © Copyright 1996 Society of Automotive Engineers, Inc.

Assessing boost-assist options for turbocharged engines using 1-D engine simulation and model predictive control

Delivering acceptable low end torque and good transient response is a significant challenge for all turbocharged engines. As downsized gasoline engines and Diesel engines make up a larger and larger proportion of the light-duty engines entering the market, the issue takes on greater significance. Several schemes have been proposed to improve torque response in highly boosted engines, including the use of electrical assist turbochargers and compressed air assist. In this paper we examine these methods with respect to their effectiveness in improving transient response and their relative performance along with some of the practical considerations for real world application. Results shown in this paper are from 1-D simulations using the Ricardo WAVE software package. The simulation model is based on a production light-duty Diesel engine modified to allow the introduction of compressed air at various points in the air-path as well as direct torque application to the turbocharger shaft (such as might be available from an electrical assist turbocharger). Whilst the 1-D simulation software provides a suitable environment for investigating the various boost assistance options, the overall air path performance also depends upon the control system. The introduction of boost assistance complicates the control in two significant ways: the system may run into constraints (such as compressor surge) that are not encountered in normal operation and the assistance introduces an additional control input. Production engine controllers are usually based on gain-scheduled PID control and extensive calibration. For this study, the non-linear nature of the engine together with the multiple configurations considered and the slower than real-time execution of 1-D models makes such an approach time consuming. Moreover, an ad-hoc approach would leave some doubt as to the fairness of comparisons between the different boost-assist options. Model Predictive Control has been shown to offer a convenient approach to controlling the 1-D simulations in a close to optimal manner for a typical Diesel VGT-EGR air path configuration. We show that the same technique can be applied to all the considered assistance methods with only modest calibration effort required. Copyright © 2012 SAE International.

World Wide Web Image Search Engines

We propose the development of a world wide web image search engine that crawls the web collecting information about the images it finds, computes the appropriate image decompositions and indices, and stores this extracted information for searches based on image content. Indexing and searching images need not require solving the image understanding problem. Instead, the general approach should be to provide an arsenal of image decompositions and discriminants that can be precomputed for images. At search time, users can select a weighted subset of these decompositions to be used for computing image similarity measurements. While this approach avoids the search-time-dependent problem of labeling what is important in images, it still holds several important problems that require further research in the area of query by image content. We briefly explore some of these problems as they pertain to shape.