Richard Stone

Correlations for the Laminar-Burning Velocity of Methane/Diluent/Air Mixtures Obtained in Free-Fall Experiments

The laminar-burning velocity of methane/air/diluent mixtures has been correlated for variations in unburnt gas temperature (within the range of 293 K to 454 K) and pressures (within the range of 0.5 to 10.4 bar), for as wide a range of mixtures as could be accommodated. The laminar-burning velocity measurements have been deduced from pressure time measurements made in near zero-gravity conditions in a spherical constant volume chamber. The correlations were obtained by a least squares fit of the data to an equation with 12 degrees of freedom. Carbon dioxide, nitrogen, and a 15% carbon dioxide/85% nitrogen mixture were diluents. The mixture of carbon dioxide and nitrogen was used to simulate the products of combustion, thus enabling measurements of the burning velocity to be made that correspond to when exhaust gas residuals (including those arising from exhaust gas recirculation) are present. The data presented here cover higher levels of diluents than previously reported, with up to 60% of either nitrogen or carbon dioxide as part of the fuel.

Particulate and Hydrocarbon Emissions from a Spray Guided Direct Injection Spark Ignition Engine with Oxygenate Fuel Blends

The blending of oxygenated compounds with gasoline is projected to increase because oxygenate fuels can be produced renewably, and because their high octane rating allows them to be used in substitution of the aromatic fraction in gasoline. Blending oxygenates with gasoline changes the fuels’ properties and can have a profound affect on the distillation curve, both of which are known to affect engine-out emissions. In this work, the effect of blending methanol and ethanol with gasoline on unburned hydrocarbon and particulate emissions is experimentally determined in a spray guided direct injection engine. Particulate number concentration and size distribution were measured using a Cambustion DMS500. These data are presented for different air fuel ratios, loads, ignition timings and injection timings. In addition, the ASTM D86 distillation curve was modeled using the binary activity coefficients method for the fuel blends used in the experiments. In general, unburned hydrocarbon emissions were reduced at low load but increased at high load for the alcohol blends. The effect on particulate emissions was dependent on the operating point: for rich mixtures the accumulation mode number concentration and count median diameter were reduced with the oxygenate blends. However, blending gasoline with oxygenates also caused the nucleation mode number concentration to increase, particularly for M85. The distillation curve modeling showed that blending oxygenates affects the distillation curve much more than would be expected from a linear blending relationship: the front end volatility is reduced a little, whilst the mid range volatility is increased significantly, particularly for methanol blends.

Knock measurement for fuel evaluation in spark ignition engines

An average energy method for quantifying knock intensity has been developed with a shifting window period; this is called the logarithmic knock intensity (LKI). To establish the engine knock conditions, a statistical analysis has been undertaken in real-time and a 1000-cycle LKI mean has been recommended as a proper criterion for defining the knock intensity. A method for eliminating the speed dependence of the LKI has also been developed. Derived from the above method, a multi-microprocessor based Knock Detector with LCD and LED displays and a D/A output has been developed.

The Influence of Ethanol Blends on Particulate Matter Emissions from Gasoline Direct Injection Engines

Particulate Matter (PM) legislation for gasoline en gines and the introduction of gasoline/ethanol blen ds, make it important to know the effect of fuel composition on PM emissions. Tests have been conducted with fuels of known composition in both a single cylinder engine and V8 engine with a three-way catalyst. The V8 engine used an unleaded gasoline (PURA) with known composition and distillation characteristics as a base fue l and with 10% by volume ethanol. The single cylinder engine used a 65% iso-octane - 35% toluene mixture as its base fuel. The engines had essentially the same co mbustion system, with a centrally mounted 6-hole sp rayguided direct injection system. Particle size distr ibutions were recorded and these have also been con verted to mass distributions. Filter samples were taken for t hermo-gravimetric analysis (TGA) to give composition information. Both engines were operated at 1500 rpm under part l oad. The tests with the single cylinder engine use d lambda of 0.9, 1.0 and 1.1 with an ignition timing sweep o f 15-45° bTDC. The trends with the stoichiometric a nd weak mixtures were less clear (the PM emissions being at low levels), but with lambda of 0.9 the trends wer e clear. For the rich mixture, advancing the ignition timing increased both PM number and mass emissions, and the use of E10 reduced the number emissions by a factor of 25-65 and the mass emissions by a factor of 2-10. The V8 tests were at stoichiometric with injection timing sweeps during induction (120 to 360° bTDC), with a reduction in both PM number and mass due to reactions in the catalyst. The earlier injection gave lo wer PM emissions and this was attributed to there being mo re time for mixture preparation, leading to a more homogeneous mixture. The addition of 10% ethanol led to an increase in PM emissions (both in terms of mass and number).

A model of the educational system

The purpose of this paper is to outline a model of the educational system designed to work out the present implications of future levels of educational activity as determined by the evolution of the demand for places on the one hand and the economic demand for the products of education on the other. The need for such a model must be apparent to all who have read the report of the Robbins Committee 1 and considered the enormous organisational problems that it sets. It is equally apparent if we consider the possibilities for spectacular improvement which applied science offers to the techniques of production. Great changes are essential if we want to achieve a substantial increase in the growth rate of our standard of living in Great Britain, along the lines that the National Economic Development Council is aiming at, and if Great Britain is to present a less flabby economic image on the international scene.

Instantaneous Exhaust Temperature Measurements Using Thermocouple Compensation Techniques

This paper discusses a method of measuring the instantaneous exhaust gas temperature by thermocouples. Measuring the exhaust gas temperature is useful for a better understanding of engine processes. Thermocouples do not measure the instantaneous exhaust gas temperature because of their limited dynamic response. A thermocouple compensation technique has been developed to estimate the time constant in situ. This method has been commissioned in a simulation study and a controlled experiment with a reference temperature. The studies have shown that the signal bandwidth has to be restricted, since noise will be amplified in the temperature reconstruction. The technique has been successfully applied to some engine exhaust measurements. A comparison between two independent pairs of thermocouples has shown that temperature variations at frequencies up to 80Hz can be recovered. The medium load results agree with a previous study, which used fast response thermometers with a bandwidth of about 50 Hz. However, the results at low load and two different speeds have highlighted the need to do some 1-D unsteady flow simulations, in order to gain more insight into the exhaust process.

Combustion of LPG in a Spark-Ignition Engine

Tax concessions promote the use of Liquefied Petroleum Gas (LPG) fuel for automotive use in Europe. Modelling of the LPG evaporation process shows the importance of drawing the liquid from the tank rather than the gas, otherwise the most volatile component (propane) is used more quickly and the composition of the remaining fuel changes. It is shown that the LPG components have similar calorific values to gasoline, however injecting the LPG as a gas into the inlet port causes a loss of volumetric efficiency and peak power.

Effect of the valve timing and the coolant temperature on particulate emissions from a gasoline direct-injection engine fuelled with gasoline and with a gasoline–ethanol blend

Variable-valve-timing technology and ethanol addition to gasoline are both considered to be effective strategies for better performance and potential improvement in the fuel economy in gasoline engines. In this study, a Jaguar V8, naturally aspirated spray-guided direct-injection engine was operated with four different valve-timing combinations using an unleaded gasoline and a gasoline–10 vol % ethanol blend. The internal exhaust gas recirculation rate and the in-cylinder gas temperature were modelled for different valve-timing strategies. The results showed that a high valve overlap led to high internal exhaust gas recirculation and a high charge temperature, which evidently improved the fuel spray atomization and reduced the particulate matter emissions. Adding 10 vol % ethanol led to a rise in the total particle number and the total particle mass in emissions by a factor of up to 2 under warm-engine conditions (with a coolant temperature of 90 °C) but led to a reduction in the total particle number and the total particle mass in emissions by up to two-thirds under cold conditions (with a coolant temperature of 20 °C). Thermogravimetric analysis tests were conducted to analyse the compositions of filter-borne particulate matter emissions, and more than 75 mass % organic material was always present. All measurements are reported for both pre- and post-three-way-catalyst samples, the latter always showing a significant reduction (a factor of about 2) in the particulate matter emissions.

Particulate Emissions from a Gasoline Homogeneous Charge Compression Ignition Engine

Particulate Emissions from a Gasoline Homogeneous Charge Compression Ignition Engine Philip Price , Richard Stone Jacek Misztal, Hongming Xu, Miroslaw Wyszynski, Trevor Wilson and Jun Qiao Department of Engineering Science, University of Oxford, OX1 3PJ, UK Department of Mechanical Engineering, University of Birmingham, B15 2TT, UK Jaguar Research, Whitley Engineering Centre, CV3 4LF, UK philip.price@eng.ox.ac.uk

Input-output and demographic accounting: A tool for educational planning

ConclusionIn this paper I have tried to bring together various forms of input-output accounting and analysis suited to dynamic problems. In the usual, static accounting system, the entries all relate to a single time-period and the set of accounts is completely closed. In the alternative, dynamic system suggested here, the inputs for a given period come, either in whole or in part, from the preceding period and the outputs go, either in whole or in part, to the succeeding period.Two types of model can be built within the framework of this dynamic accounting structure: the conventional input-output model, in which the input coefficients are fixed; and an allocation model, in which the output co-efficients are fixed. The conventional model is appropriate to the analysis of production flows; the allocation model to that of demographic flows. These two models provide us with the main building blocks for an educational model, since as far as the human inputs are concerned the educational system is simply a partition of the demographic system, and as far as the economic inputs are concerned it is a partition of the productive system. A first attempt at combining the two was described in my earlier article.