energies Article Flame Front Propagation in an Optical GDI Engine under Stoichiometric and Lean Burn Conditions Santiago Martinez 1 ID , Adrian Irimescu 2, Simona Silvia Merola 2,* ID , Pedro Lacava 1 and Pedro Curto-Riso 3 ID 1 Technological Institute of Aeronautics, São Jose dos Campos 12228-900, Brazil; santiagofi
[email protected] (S.M.);
[email protected] (P.L.) 2 Istituto Motori, Consiglio Nazionale delle Ricerche, 80125 Napoli, Italy;
[email protected] 3 Department of Applied Thermodynamics, University of La República, Montevideo 11200, Uruguay; pcurto@fing.edu.uy * Correspondence:
[email protected]; Tel.: +39-081-717-7224 Received: 13 July 2017; Accepted: 30 August 2017; Published: 5 September 2017 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.