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Cambridge, United Kingdom

McTaggart-Cowan G.P.,Loughborough University | Cong S.,Loughborough University | Garner C.P.,Loughborough University | Wahab E.,Ford Motor Company | Peckham M.,Cambustion Ltd
Journal of Engineering for Gas Turbines and Power | Year: 2012

This work elucidated which engine operating parameters have the greatest influence on Low temperature diesel combustion (LTC) and emissions. Key parameters were selected and evaluated at low and intermediate speed and load conditions using fractional factorial and Taguchi orthogonal experimental designs. The variations investigated were: about ± 5% in EGR rate, fuel injection quantity and engine speed respectively; and ± 10°C in intake charge temperature. The half-fractional factorial results showed that the interactions among these parameters were negligible for a specific load/speed point. The Taguchi orthogonal method could be used as an efficient DoE tool for studying the multi-parameter small-scale transients' that a diesel engine would be likely to encounter when operating in LTC modes. LTC showed the most significant sensitivity to EGR rate variations, where an increase from 60% to 63% in EGR rate doubled THC and CO emissions and reduced combustion stability. LTC was also sensitive to the fuel injection quantity with an increase in injected mass lowering the overall oxygen-fuel ratio and thereby increasing THC and CO emissions. These two parameters influenced the oxygen concentration in the intake charge; which was identified to be a decisive parameter for the LTC combustion and emissions. Intake charge temperature affected the total charge quantity trapped in the cylinder and showed noticeable influence on CO emissions for the low speed intermediate load condition. Variations in engine speed showed a negligible influence on the LTC combustion processes and emissions. © 2012 American Society of Mechanical Engineers.

Cong S.,Loughborough University | McTaggart-Cowan G.P.,Loughborough University | Garner C.P.,Loughborough University | Wahab E.,Ford Motor Company | Peckham M.,Cambustion Ltd
Combustion Science and Technology | Year: 2011

The work presented in this article investigates the three distinct phases of low temperature diesel combustion (LTC). Diesel LTC followed a cool flame-negative temperature coefficient (NTC)-high temperature thermal reaction (main combustion) process. The in-cylinder parameters, such as the charge temperature, pressure, and composition, had noticeable influences on these combustion stages. The NTC was strongly temperature-dependent, with higher temperatures inducing both an earlier onset of NTC and a more rapid transition from NTC to the main combustion process. An increase in the intake charge temperature led to an earlier occurrence of NTC and a reduction in the heat released during the cool flame regime. A higher fuel injection pressure improved fuel mixing and enhanced the low temperature (pre-combustion) reactions, which in turn led to an earlier appearance of the cool flame regime and more heat release during this phase. This increased the charge temperature and led to earlier onset of the NTCregime.Ahigher exhaust gas recirculation (EGR) rate reduced the intake charge oxygen concentration and limited the low temperature reaction rates. This reduced the heat release rate during cool flame reaction phase, leading to a slower increase in charge temperature and a longer duration of the NTC regime. This increased the ignition delay for the main combustion event. The injection timing showed a less significant influence on the cool flame reaction rates and NTC phase compared to the other parameters. However, it had a significant influence on the main combustion heat release process in terms of phasing and peak heat release rate. Copyright © Taylor & Francis Group, LLC.

Collings N.,University of Cambridge | Rongchai K.,University of Cambridge | Symonds J.P.R.,Cambustion Ltd
Journal of Aerosol Science | Year: 2014

A High Temperature Condensation Particle Counter (HT-CPC) is described that operates at an elevated temperature of up to ca. 300. °C such that volatile particles from typical combustion sources are not counted. The HT-CPC is functionally identical to a conventional CPC, the main challenge being to find suitable non-hazardous working fluids, with good stability, and an appropriate vapour pressure. Some key design features are described, and results of modelling which predict the HT-CPC counting efficiency. Experimental results are presented for several candidate fluids when the HT-CPC was challenged with ambient, NaCl and diesel soot particles, and the results show good agreement with modelled predictions, and confirm that counting of particles of diameters down to at least 10. nm was achievable. Possible applications are presented, including measurement of particles from a diesel car engine and comparison with a near PMP system. © 2014 Elsevier Ltd.

Whitehead J.D.,University of Manchester | Irwin M.,University of Manchester | Irwin M.,Cambustion Ltd | Allan J.D.,University of Manchester | And 3 more authors.
Atmospheric Chemistry and Physics | Year: 2014

Water uptake by aerosol particles controls their ability to form cloud droplets, and reconciliation between different techniques for examining cloud condensation nuclei (CCN) properties is important to our understanding of these processes and our ability to measure and predict them. Reconciliation between measurements of sub-saturated and supersaturated aerosol particle water uptake was attempted at a wide range of locations between 2007 and 2013. The agreement in derived number of CCN (NCCN or particle hygroscopicity was mixed across the projects, with some data sets showing poor agreement across all supersaturations and others agreeing within errors for at least some of the supersaturation range. The degree of reconciliation did not seem to depend on the environment in which the measurements were taken. The discrepancies can only be attributable to differences in the chemical behaviour of aerosols and gases in each instrument, leading to under-or overestimated growth factors and/or CCN counts, though poorer reconciliation at lower supersaturations can be attributed to uncertainties in the size distribution at the threshold diameter found at these supersaturations. From a single instrument, the variability in NCCN calculated using particle hygroscopicity or size distribution averaged across a project demonstrates a greater sensitivity to variation in the size distribution than chemical composition in most of the experiments. However, the discrepancies between instruments indicate a strong requirement for reliable quantification of CCN in line with an improved understanding of the physical processes involved in their measurement. Without understanding the reason for discrepancies in the measurements, it is questionable whether quantification of CCN behaviour is meaningful. © 2014 Author(s).

Sarangi A.K.,Loughborough University | Garner C.P.,Loughborough University | McTaggart-Cowan G.P.,Loughborough University | Davy M.H.,Loughborough University | And 2 more authors.
Proceedings of the Institution of Mechanical Engineers, Part D: Journal of Automobile Engineering | Year: 2012

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 mass) split-injection strategy to variations in the key engine operating parameters. Experiments were performed at operating conditions corresponding to a gross indicated mean effective pressure of 500 kPa at an engine speed of 1500 r/min in a 0.51 l single-cylinder high-speed direct-injection diesel engine. The paper presents the effects of different relative fuel injection timings at a variable intake oxygen mass fraction (10.5% and 12%) at a constant intake pressure (120 kPa, absolute) on the smoke, total hydrocarbon and carbon monoxide emissions with the split-main-injection strategy. The effects of a variable fuel injection pressure (90 MPa and 110 MPa) on diesel low-temperature combustion with split injection are also reported, as are the effect of an increased intake pressure (150 kPa, absolute). The combined effects of the operating parameters and the fuel injection timing on the smoke, nitrogen oxide, total hydrocarbon and carbon monoxide emissions and the gross indicated specific fuel consumption are described. For selected operating conditions, the cycle-resolved spray and combustion processes are visualized together with the flame temperature measurement using two-colour optical pyrometry to understand the combustion phenomena occurring in the split-injection strategy. The results of the optical studies show that different low-temperature combustion operating conditions producing similarly low levels of 'engine-out' smoke emissions have substantially different histories of soot formation and soot oxidation. An increase in the intake oxygen mass fraction reduced the total hydrocarbon emissions and the gross indicated specific fuel consumption at a given intake pressure, while a higher intake pressure reduced them further. Although significant soot formation took place from the second injection event, the majority of the soot was subsequently oxidized because of a slightly higher flame temperature and slightly higher oxygen concentration than in single-injection high-exhaust-gas-recirculation low-temperature combustion. A higher injection pressure did not have any significant effect on the emissions and the gross indicated specific fuel consumption. © IMechE 2012.

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