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Energies 2017, 10(9), 1337; https://doi.org/10.3390/en10091337

Flame Front Propagation in an Optical GDI Engine under Stoichiometric and Lean Burn Conditions

1
Technological Institute of Aeronautics, São Jose dos Campos 12228-900, Brazil
2
Istituto Motori, Consiglio Nazionale delle Ricerche, 80125 Napoli, Italy
3
Department of Applied Thermodynamics, University of La República, Montevideo 11200, Uruguay
*
Author to whom correspondence should be addressed.
Received: 13 July 2017 / Revised: 29 August 2017 / Accepted: 30 August 2017 / Published: 5 September 2017
(This article belongs to the Section Energy Fundamentals and Conversion)

Abstract

Lean fueling of spark ignited (SI) engines is a valid method for increasing efficiency and reducing nitric oxide (NOx) emissions. Gasoline direct injection (GDI) allows better fuel economy with respect to the port-fuel injection configuration, through greater flexibility to load changes, reduced tendency to abnormal combustion, and reduction of pumping and heat losses. During homogenous charge operation with lean mixtures, flame development is prolonged and incomplete combustion can even occur, causing a decrease in stability and engine efficiency. On the other hand, charge stratification results in fuel impingement on the combustion chamber walls and high particle emissions. Therefore, lean operation requires a fundamentally new understanding of in-cylinder processes for developing the next generation of direct-injection (DI) SI engines. In this paper, combustion was investigated in an optically accessible DISI single cylinder research engine fueled with gasoline. Stoichiometric and lean operations were studied in detail through a combined thermodynamic and optical approach. The engine was operated at a fixed rotational speed (1000 rpm), with a wide open throttle, and at the start of the injection during the intake stroke. The excess air ratio was raised from 1 to values close to the flammability limit, and spark timing was adopted according to the maximum brake torque setting for each case. Cycle resolved digital imaging and spectroscopy were applied; the optical data were correlated to in-cylinder pressure traces and exhaust gas emission measurements. Flame front propagation speed, flame morphology parameters, and centroid motion were evaluated through image processing. Chemical kinetics were characterized based on spectroscopy data. Lean burn operation demonstrated increased flame distortion and center movement from the location of the spark plug compared to the stoichiometric case; engine stability decreased as the lean flammability limit was approached. View Full-Text
Keywords: spark ignition engine; direct injection; flame imaging; spectroscopy; lean operation spark ignition engine; direct injection; flame imaging; spectroscopy; lean operation
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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. (CC BY 4.0).
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Martinez, S.; Irimescu, A.; Merola, S.S.; Lacava, P.; Curto-Riso, P. Flame Front Propagation in an Optical GDI Engine under Stoichiometric and Lean Burn Conditions. Energies 2017, 10, 1337.

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