Martin Davy

• University of Oxford

In fluid mechanics research, data gathered from measurements and simulations may be challenging to interpret due to complexities such as transience, non-linearity, and high dimensionality. Velocity data from the airflow through an internal combustion engine often exhibit such properties; nevertheless, accurate characterizations of these airflows ar...

Validation of Reynolds-averaged Navier–Stokes (RANS) simulation results against experimental data such as flow measurements from particle image velocimetry (PIV) remains a challenge for the development of thermal propulsion systems. This is partly due to cycle-to-cycle variations (CCVs) in the air motion and partly due to uncertainties in the PIV m...

Laminar burning velocities (LBV) and Markstein lengths of spherical flames of n-heptane (H), iso-octane (O), and ethanol (E) and their binary and ternary mixtures (in equal volume fractions) at elevated pressures and temperatures are experimentally investigated. Measurements are performed in a constant volume combustion vessel using two distinct te...

Numerical simulations are performed to study the mechanism of deflagration to detonation transition (DDT) in a pre-/main- chamber combustion system. The fully compressible Navier-Stokes equations, coupled with a chemical-diffusive model in a stoichiometric ethylene-oxygen mixture, are solved with a high-order numerical algorithm on a dynamically ad...

This study presents the first demonstration of Marshall and Hinton’s empirical correlation for laminar burning velocity (LBV) applied to iso-octane/ethanol blends. The “Oxford” correlation is first validated for neat iso-octane and ethanol combustion against the outputs of three different chemical kinetics mechanisms and experimental data from the...

Conditional Source-term Estimation (CSE) is a combustion model based on the conditional moment hypothesis where transport equations for reactive species are conditionally averaged on conserved scalars. Major advantages of this strategy are the reduced spatial dependence of the conditional averages and negligible fluctuations around the conditional...

The predictive ability of artificial neural networks where a large number of experimental data are available, has been studied extensively. Studies have shown that ANN models are capable of accurately predicting NOx emissions from engines under various operating conditions and different fuel types when trained well. One of the major advantages of a...

In diesel engines, high levels of exhaust gas recirculation can be used to achieve low-temperature combustion, resulting in low emission levels of both nitrogen oxides (NO x ) and particulate matter. This work studied the effects of varying the intake manifold pressure on in-cylinder combustion processes and engine-out emissions from a light-duty s...

This article considers the application and refinement of artificial neural network methods for the prediction of NO x emissions from a high-speed direct injection diesel engine over a wide range of engine operating conditions. The relative computational cost and performance of two backpropagation algorithms, Levenberg–Marquardt and Bayesian regular...

A novel combustion modelling approach is proposed here to study the transient effects of diesel spray. Conditional Source-term Estimation (CSE) is a combustion model which invokes the Conditional Moment Closure (CMC) hypothesis to provide an approximation of the mean chemical source term in an averaged transport equation. Unlike CMC, where transpor...

In this study, the role of turbulence-chemistry interaction in diesel spray auto-ignition, flame stabilization and end of injection phenomena is investigated under engine relevant "Spray A" conditions. A recently developed diesel spray combustion modeling approach, Conditional Source-term Estimation (CSE-FGM), is coupled with Reynolds-averaged Navi...

Prism Signal Processing is a new recursive FIR technique offering rapid filter design and calculation. It has previously been applied to Coriolis mass flow metering to generate fast (48 kHz) flow measurement updates, facilitating for the first time the direct mass flow measurement of individual fuel pulses injected into a laboratory diesel fuel inj...

div class="section abstract"> In-cylinder temperatures and their cyclic variations strongly influence many aspects of internal combustion engine operation, from chemical reaction rates determining the production of NOx and particulate matter to the tendency for auto-ignition leading to knock in spark ignition engines. Spatially resolved measurement...

Engine-out NOx emissions from diesel engines continue to be a major topic of research interest. While substantial understanding has been obtained of engine-out (i.e., before any aftertreatment) NOx formation and reduction techniques, not least exhaust gas recirculation (EGR) which is now well established and fitted to production vehicles, much less...

As the control of real driving emissions continues to increase in importance, the importance of understanding emission formation mechanisms during engine transients similarly increases. Knowledge of the NO 2 /NO x ratio emitted from a diesel engine is necessary, particularly for ensuring optimum performance of NO x aftertreatment systems. In this w...

Engine-out NOx emissions from diesel engines continue to be a major topic of research interest. While substantial understanding has been obtained of engine-out (i.e. before any aftertreatment) NOx formation and reduction techniques, not least EGR which is now well established and fitted to production vehicles, much less data are available on cycle...

It is known that low-temperature combustion (LTC) strategies can help simultaneously reduce nitrogen oxides (NOx) and particulate matter (PM) emissions from diesel engines to very low levels. However, it is also known that LTC may cause emissions of unburned hydrocarbons (UHC) to rise — especially in low load operating conditions. Recent studies in...

Crank angle-resolved temperatures have been measured using laser induced grating spectroscopy (LIGS) in a motored reciprocating compression machine to simulate diesel engine operating conditions. A portable LIGS system based on a pulsed Nd:YAG laser, fundamental emission at 1064 nm and the fourth harmonic at 266 nm, was used with a c.w. diode-pumpe...

Engine out emissions from a diesel engine are highly dependent on the nature of the fuel/air interactions in cylinder, which in turn depend on the detail of the fuel injection process. High temperatures, which promote soot oxidation, also promote NOx formation. Carefully controlling these interactions can lead to cleaner combustion resulting in low...

Swirl flaps are commonly used in modern diesel engines to compensate for low in-cylinder air motion at low engine speeds and increase in-cylinder swirl. Increasing the air motion improves fuel-air mixing and leads to lower smoke and CO emissions; however the improved mixing leads to shorter combustion durations and hence a rise in in-cylinder tempe...

Knowledge of fuel mass injected in an individual cycle is important for engine performance and modeling. At the moment, such measurements are not possible on-engine or in real-time. In this paper, a new method using Coriolis flow meters (CFMs) and a new, patented, signal processing technique, known as the Prism, is introduced. CFMs are extensively...

A new reflected shock tube facility, the Cold Driven Shock Tube (CDST), has been designed, built and commissioned at the University of Oxford for investigating IC engine fuel spray physics and chemistry. Fuel spray and chemical kinetics research requires its test gas to be at engine representative pressures and temperatures. A reflected shock tube...

Understanding engine-out NOx and soot emissions from light-duty diesel engines is vital for improving combustion system design and ultimately for reducing aftertreatment requirements. In this work two piston bowl shapes, a standard re-entrant bowl and a bowl with a stepped lip, are tested experimentally and numerically at two part-load operating po...

The effects of different exhaust gas recirculation (EGR) strategies on engine efficiency and the resulting energy flows at two speed/load conditions (1500 r/min/6.8 bar net indicated mean effective pressure (nIMEP) and 1750 r/min/13.5 bar nIMEP) were studied using a first law analysis approach. The EGR strategies tested were as follows: cooled high...

A new, networked approach to signal processing, efficient for both design and real-time computation, is proposed to match the requirements of the Internet of Things (IoT). The Prism is a novel FIR filter which is fully recursive: the computational cost per sample is low and independent of the filter window length. The design cost is also low: any d...

Measurement of exhaust gas pressure at high speed in an engine is important for engine efficiency, computational fluid dynamics analysis, and turbocharger matching. Currently used piezoresistive sensors are bulky, require cooling, and have limited lifetimes. A new sensor system uses an interferometric technique to measure pressure by measuring the...

The spatial and temporal distribution of fuel and air within the combustion chamber directly influences ignition, combustion and emissions formation in diesel engines. These fuel-air interactions are affected by details of the combustion chamber geometry and fuel injection parameters. This paper investigates the effects of piston bowl geometry and...

This article describes the effects of intake-port throttling on diesel low-temperature combustion at a low and medium load condition. These conditions were known for their characteristically high hydrocarbon emissions predominantly from over-mixed and under-mixed mixture zones, respectively. The investigation was carried out to supplement current f...

Prism signal processing is a new recursive FIR technique that facilitates the rapid tracking of sinusoidal signals, such as those used in a Coriolis Mass Flow Meter (CMFM). A Prism-based CMFM prototype has been developed using a commercial flowtube and a dual ARM processor-based transmitter, which is capable of generating flow measurement updates a...

A presentation given at the FMI presenting updated Fast NGC results including resonant frequency effects.

Thermometry using laser-induced grating spectroscopy (LIGS) is reported using a high-repetition rate laser system, extending the technique to allow time-resolved measurements of gas dynamics. LIGS signals were generated using the second harmonic output at 532 nm of a commercially available high-repetition rate Nd:YAG laser with nitrogen dioxide as...

Fast NGC – advanced fuel flow measurement Knowing how much fuel is being used in fuel injectors essential for monitoring both gasoline and diesel engine performance. Current technology allows us to do this for the whole engine over many injections, but not for each injection event. This project has taken technology already used widely in the oil an...

Direct injection spark ignition (DISI) engines produce more particulate matter (PM) emissions than port fuel injected (PFI) engines, but their greater specific output and lower CO2 emissions have led to widespread use. Oxygenate components are seen as a useful way of decarbonising road transport. Fuels have been splash blended with ethanol, methano...

A model for the evaporation of a multi-component fuel droplet is presented that takes account of temperature dependent fuel and vapour properties, evolving droplet internal temperature distribution and composition, and enhancement to heat and mass transfer due to droplet motion. The effect on the internal droplet mixing of non-ideal fluid diffusion...

A general multi-component model is presented here that builds on currently available models to include non-ideal vapour liquid equilibrium (VLE) and internal droplet liquid diffusion. Both of these effects can influence droplet lifetime estimates, particularly when there are oxygenated components in the fuel mixture, as is current industry practice...

When appropriately sourced, bioethanol and biodiesel fuels provide an opportunity for nations to increase their energy independence or to reduce greenhouse gas emissions by supplying energy-dense fuels which are miscible with fossil-derived gasoline and diesel. These fuels can be used in low concentrations in vehicles with no modifications; in the...

An explicit model for the evaporation of a spherical single component fuel droplet is presented that takes account of temperature dependent fuel and vapour properties, evolving droplet internal temperature distribution and enhancement to heat and mass transfer due to droplet motion. This has been developed to model multi-component fuels, using non-...

Low-temperature combustion in diesel engines offers attractive benefits through simultaneous reduction in the nitrogen oxide emissions and the soot emissions. However, it is known that the in-cylinder conditions typical of low-temperature combustion operation tend to produce high emissions of unburned hydrocarbons and carbon monoxide, reducing the...

The operation of diesel low-temperature combustion engines is currently limited to low-load and medium-load conditions. Mode transitions between diesel low-temperature combustion and conventional diesel operation and between conventional diesel operation and diesel low-temperature combustion are therefore necessary to meet typical legislated drivin...

Particulate Number (PN) standards in the proposed Euro 6 emissions legislation pose an imminent challenge for engine designers during the startup and warm-up phases of cold Direct Injection Spark Ignition (DISI) engines.To achieve catalyst light-off in the shortest time, engine strategies are often employed which inherently use more fuel to attain...

A comparative study into the effects of total volume flow rate, methane ‘residency time’, methane volume flow rate, and steam-to-carbon ratio on the steam-methane reforming process was performed in a model Direct Internal Reforming SOFC (DIR-SOFC) reformer operating in steady state at a nominal temperature of 973 K. The spatial distributions of maj...

Particulate Matter (PM) emissions reduction is an imminent challenge for Direct Injection Spark Ignition (DISI) engine designers due to the introduction of Particulate Number (PN) standards in the proposed Euro 6 emissions legislation aimed at delivering the next phase of air quality improvements. An understanding of how the formation of combustion...

Low temperature combustion (LTC) in diesel engines offers attractive benefits through simultaneous reduction of nitrogen oxides and soot. However, it is known that the in-cylinder conditions typical of LTC operation tend to produce high emissions of unburned hydrocarbons (UHC) and carbon monoxide (CO), reducing combustion efficiency. The present st...

Diesel engine emissions of oxides of nitrogen and smoke can be reduced simultaneously through the use of high levels of exhaust gas recirculation to achieve low-temperature combustion. However, single fuel injection per cycle diesel low-temperature combustion is also characterized by high fuel consumption and high total unburned hydrocarbons and ca...

This study presents an investigation into the feasibility of implementing a multiple injection strategy in a single cylinder DISI optical engine for the purpose of reducing in-cylinder wall wetting and thereby PM and HC emissions. The potential advantage of adopting a triple injection strategy compared to a single injection strategy is analysed usi...

High-EGR diesel low temperature combustion breaks the traditional diesel NOx-PM trade-off, thereby facilitating ultra-low NOx emissions with simultaneously low smoke emissions. High-EGR LTC is currently limited to low and medium load and speed conditions. Therefore, in order to implement a high-EGR diesel LTC strategy in a passenger vehicle, a tran...

This paper shows that a split-fuel-injection strategy can achieve robust, near-zero smoke and nitrogen oxide emissions at reduced exhaust gas recirculation levels under low-temperature combustion conditions. The overall objective of the work was to investigate the sensitivity (in terms of the engine emissions and the fuel economy) of a 50:50 (by ma...

In the railroad industry a friction modifying agent may be applied to the rail or wheel in the form of a liquid jet. In this mode of application the interaction between the high-speed liquid jet and a fast moving surface is important. Seven different Newtonian liquids with widely varying shear viscosities were tested to isolate the effect of viscos...

This paper outlines the development of a comprehensive numerical framework for the partially stratified charge (PSC) lean-burn natural gas engine. A 3D model of the engine was implemented to represent fluid motion and combustion. The spark ignition model was based on the works of Herweg and Maly (1992, "A Fundamental Model for Flame Kernel Formatio...

The effects of hydrogen addition on the ignition and combustion of a high-pressure methane jet in a quiescent charge of high-temperature, medium-pressure air were investigated numerically and experimentally. Subsequently, the results of these two fundamental studies were applied to the interpretation of combustion and emissions measurements from a...

This work reports the development of a novel high temperature, optically-accessed experimental facility and optical methods for Solid Oxide Fuel Cell (SOFC) research at the University of British Columbia (UBC). Vibrational Raman spectroscopy is applied to determine the flow-wise distributions of key gaseous species in a model Direct Internal Reform...

In the railroad industry a friction modifying agent may be applied to the rail or wheel in the form of a liquid jet. In this mode of application the interaction between the high-speed liquid jet and a fast moving surface is important. Seven different Newtonian liquids with widely varying shear viscosities were tested to isolate the effect of viscos...

A Reynolds averaged Navier–Stokes (RANS) based combustion model, which incorporated the conditional source-term estimation (CSE) method for the closure of the chemical source term and the trajectory generated low-dimensional manifold (TGLDM) method for the reduction of detailed chemistry, was applied to predict the OH radical distribution in a comb...

Broadband XeCl excimer lasers operating at 308 nm are not currently used in the field of gas phase vibrational Raman spectroscopy (VRS). An explanation as to why alternative wavelengths, and in particular tuneable, narrowband lasers are currently preferred for gas phase VRS is presented in addition to demonstrating a setup which makes the XeCl lase...

To better understand spray coating in field conditions, we have examined the effect of a cross-flow on two different airblast sprays, one comprising water and the other a viscoelastic industrial coating. Using particle image velocimetry, we measured the time-averaged spatial distribution of droplet velocity over a wide range of spray:cross-flow mom...

Viscoelastic liquids, such as paints and coatings, are widely known to be more difficult to atomize than typical Newtonian liquids. What is not known, however, is how such a difference affects spray coating in field conditions. To address this, we have examined the effect of a cross-flow on two different air-blast sprays, one comprising water and t...

This is a pre-print of an article published in the journal, Combustion Science and Technology [© Taylor & Francis]. The definitive version is available at: http://dx.doi.org/10.1080/00102200802612260 The effects of adding ethane or nitrogen on the ignition and combustion of a non-premixed high-pressure methane-air jet have been investigated using f...

Motivated by the need to improve spray coating transfer efficiencies, results are presented from an experimental investigation into the interaction between an air-blast spray and a high-speed moving surface. Three model elastic liquids of varying polymer molecular weight and three inelastic liquids of varying shear viscosity were used to isolate th...

Motivated by the need to improve spray coating, an experimental investigation into viscoelastic atomization using preformulated model test liquids is presented. These test liquids had similar values of surface tension, density, and rate-independent shear viscosity, but varying extensional viscosity. Through the use of these test liquids, the effect...

The partially stratified charge (PSC) injection ignition strategy aims to improve thermal efficiency and reduce emissions of lean-burn spark-ignited internal combustion engines by extending the lean limit of operation. The object of the current study is to characterize the pre-ignition formation of the fuel plume in the vicinity of the PSC spark pl...

An experimental investigation of the autoignition and emission characteristics of transient turbulent gaseous fuel jets in heated and compressed air was conducted in a shock tube facility. Experiments were performed at an initial pressure of 30 bar with initial oxidizer temperatures ranging from 1200 to 1400 K, injection pressures ranging from 60 t...

  Conventional propeller test facilities such as tow tanks, cavitation tunnels and the open sea have various limitations such as cost, accessibility, size and accuracy. An aerodynamic marine propeller test facility has been developed at the University of British Columbia to allow for performance evaluations of full-size marine propellers in the hig...

An experimental study into the sheet breakup mechanisms of two direct-injection gasoline pressure-swirl atomizers has been performed under conditions of varying fuel pressure and injector back pressure. A novel method of illumination, which allows a single thickness of the hollow-cone spray to be examined, has been developed. The results of the stu...

The effects of impinging airflow on the near nozzle characteristics of an inwardly opening, high pressure-swirl atomiser are investigated in an optically-accessed, steady-state flow rig designed to emulate the intake flow of a typical, side-injected, 4-valve gasoline direct-injection combustion system. The results indicate that the impinging airflo...

Preliminary observations are presented from an experimental investigation into the interaction between an air-blast spray of both Newtonian and non-Newtonian liquids and a moving surface. Two PEO solutions of varying molecular weight of 100K and 300K were sprayed to study the effect of elasticity and three concentrations of glycerin in water were s...

This paper presents the results of an experimental study into the liquid sheet break-up mechanisms of high-pressure swirl atomizers of the type commonly used in direct-injection spark-ignition (DISI) engines. Sheet disintegration was investigated at two fuel pressures: 5 and 10 MPa, and three ambient back pressures: 50, 100 (atmospheric) and 200 kP...

The results of a numerical and experimental investigation into the evaporation characteristics of the 3-pentanone–isooctane binary system are presented. The behaviour of the system is shown to be nonideal, exhibiting positive deviations from Raoult's law. Thus, the evaporation characteristics of 3-pentanone–isooctane mixtures are shown to be contro...

Two-dimensional Mie-scattering and laser-induced fluorescence techniques were applied to investigate the effects of fuel composition on mixture formation within a firing direct-injection spark-ignition (DISI) engine. A comparison was made between the spray characteristics and in-cylinder fuel distributions resulting from the use of a typical multi-...

In the railroad industry a friction modifying agent may be applied to the track in the form of a liquid jet. In this mode of application the interaction between the high speed liquid jet and a fast moving surface is important. Seven different Newtonian liquids with widely varying shear viscosities were tested to isolate the effect of vis-cosity fro...