The Oxford Cold Driven Shock Tube (CDST) for fuel spray and chemical kinetics research

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 generates these extreme conditions in the test gas for short durations (order milliseconds) by transiently compressing it through a reflected shock process. The CDST has been designed for a nominal test condition of 6 MPa, 900 K slug of air (300 mm long) for a steady test duration of 3 ms. The facility is capable of studying reacting mixtures at higher pressures (up to 150 bar) than other current facilities, whilst still having comparable size (100 mm diameter) and optical access to interrogate the fuel spray with high speed imaging and laser diagnostics. Future data gathered will support fundamental research for IC engine and fuel technologies leading to even higher thermal efficiency along with a reduction in emissions, and provide high quality, repeatable validation data for advanced model development. This paper describes the scope of the facility's capabilities, aspects of its design, details of the instrumentation, and the axially mounted single hole diesel injector

Spray development with in-cylinder pressure and particulate matter measurements in a GDI engine with optical access: Effects of fuel volatility

Particulate matter emissions are subject to legislation and can occur at significantly higher levels with Gasoline Direct Injection (GDI) engines than Port Fuel Injection (PFI) engines. This has to be linked to mixture preparation for which the fuel spray behaviour is fundamental. Spray behaviour is characterised here in terms of the saturation pressure ratio - the ratio of fuel saturation pressure to the in-cylinder pressure which can vary significantly during the cycle; especially when the engine is boosted. Mie scattering images with semi-quantitative analysis is used to quantify spray development, along with the use of a presence probability analysis. The particulate measurement experiments (using a Cambustion DMS500) show that fuel volatility has a beneficial impact on reducing particulate matter emissions, even if flash boiling does not occur. Flash boiling did not necessarily reduce the particulate number but it did reduce the mean particulate size

Evaluation of in-cylinder endoscopic two-colour soot pyrometry of diesel combustion

Flame temperature and soot concentration imaging was performed using endoscopic two-colour (2C) soot pyrometry to investigate the characteristics of in-cylinder diesel engine combustion processes and pro- vide validation data for engine simulation and design. To appropriately interpret the 2C image results, this paper focuses on the uncertainty and challenges of the technique, the line-of-sight nature of the measurement and presents comparable information for validation exercises. A line-of-sight flame light intensity model was created to explore how the temperature T and soot concentration KL measured by the 2C technique can relate to non-uniform flame temperature and soot distributions. It was found that T and KL measured from the 2C technique were likely to relate differently to the actual distribution de- pending on where in the flame the measurement was taken and on assumptions made about the flame spatial structure. Assessment has been made of the range of the maximum and minimum flame tem- peratures (assumed to correspond to reaction zone temperature and flame centreline respectively) that are consistent with measured temperature T and soot concentration KL . The analysis of uncertainties, flame temperature and soot distribution along the line-of-sight, and image averaging allows for better quantitative comparison of 2C soot pyrometry images to CFD simulation, which increases confidence in simulation-driven engine development.</p

Cycle-to-cycle variation analysis of two-colour PLIF temperature measurements calibrated with laser induced grating spectroscopy in a firing GDI engine

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 measurements of temperature can provide insights into such processes and enable validation of Computational Fluid Dynamics simulations used to model engine performance and guide engine design. This work uses a combination of Two-Colour Planar Laser Induced Fluorescence (TC-PLIF) and Laser Induced Grating Spectroscopy (LIGS) to measure the in-cylinder temperature distributions of a firing optically accessible spark ignition engine. TC-PLIF performs 2-D temperature measurements using fluorescence emission in two different wavelength bands but requires calibration under conditions of known temperature, pressure and composition. Here the TC-PLIF technique is calibrated in-situ using high precision (<1%) LIGS point measurements. Temperature distributions were recorded during the compression stroke for fired operation with Direct Injection and with Plenum Fuel Injection of three two-component fuels containing toluene and iso-octane. Temperature inhomogeneity was observed for all fuels and injection strategies, with mm-scale regions having temperatures up to 10% higher than the local environment. Charge cooling of 3% due to direct injection was resolved. Proper Orthogonal Decomposition (POD) was used to quantify the cycle-to-cycle variation of the temperature data. Low-order POD modes featured most of the cyclic variation in temperature and the corresponding mode coefficients were used to investigate correlations with combustion analysis, fuel injection strategies and toluene content of the fuel. Additionally, the low-order POD mode coefficients provided an opportunity to identify cycles containing local hotspots or outlier measurements