Claudia M. Fajardo

PIV, high-speed PLIF and chemiluminescence imaging for near-spark-plug investigations in IC engines

Measurements of the local flow and mixture condition near the spark plug of internal combustion engines are important to characterize their influence on ignition and combustion performance. This is especially true for direct-injection engines where limited time is available for mixture formation and optimum stratification of the fuel/air mixture to achieve best performance. Transient processes need to be visualized in an optically challenging environment. The application of digital Particle Image Velocimetry (PIV) for flow field measurements along with crank angle-resolved planar laser induced fluorescence (PLIF) and chemiluminescence imaging is discussed in the context of investigations of a highly stratified sprayguided direct-injection engine. Flow fields were captured in a firing optical single-cylinder engine to study the interaction of the fast spray and the underlying in-cylinder tumble flow. The impingement of the fuel spray on the spark plug electrodes and subsequent dispersion of the fuel cloud was filmed at a rate of 12kHz with a new PLIF technique using a diode-pumped Nd:YAG laser. Subsequent flame development and combustion progress could be followed via high-speed imaging of OH* chemiluminescence. This approach was also combined with double- pulse PLIF imaging of fuel distributions.

Simulation of an Intake Manifold Preheater for Cold Engine Startup

Ensuring consistent, reliable diesel engine startups in cold temperatures is of utmost importance in a number of applications. Under extreme temperatures, the use of glow plugs is complemented by intake manifold heaters. In these, the energy released from combustion increases the intake air temperature before the air enters the main combustion chamber. Since the process also alters the stoichiometry of the fuel-air mixture at the intake ports, the preheater operation must be optimized in order to guarantee successful and reliable in-cylinder combustion during engine startups. This paper describes the development of an intake manifold model incorporating an air preheater for application in a diesel engine. The model was created using a commercial, one-dimensional simulation tool and its default heat transfer model was modified in-house for the present application. The model was validated against experimental data and subsequently used to quantify the concentration of combustion product species at the intake runners, as well as intake charge dilution. The experimental and predicted intake runner gas temperatures agreed within 15%. Results showed that the effective equivalence ratio might increase up to 2.6 after the first 15 s of cranking, with 12.5% reduction of the O2 concentration in the intake charge.

High-Speed UV Particle Image Velocimetry

Turbulence studies in engines require velocity data at rates that resolve relevant time scales. An ultra-violet particle image velocimetry technique was devised and applied to a fired engine to capture velocity maps at 6 kHz.