Tracer-Based High-Speed Laser-Induced Fluorescence Measurements Of Temperature And Fuel Concentration Fields In A Rapid Compression Expansion Machine

Abstract

Tracer planar laser-induced fluorescence (PLIF) using 1-methylnaphthalene (1-MN) is applied to study temperature and fuel courses during compression in a rapid compression expansion machine (RCEM). A burst mode Nd:YAG-laser at 266 nm is utilized for excitation of tracer fluorescence at a repetition rate of 7.5 kHz. A high-speed intensified CMOS camera equipped with an image doubler is applied for 2-color LIF (2c-LIF). The measurements were conducted in nitrogen atmosphere for which a calibration curve is presented that was generated in a flow cell. The temperature and fuel concentration fields are very homogeneous at early points in time during compression, however, inhomogeneities in terms of millimeter-sized hot and cold gas regions can be found especially near top dead center (TDC). These inhomogeneities were also visible in the fuel partial density field and are due to the distinct heat transfer between the hot gas and the cool walls, and probably also because of roll-up vortices induced by the piston movement. Especially at TDC the minimal gas temperature is about 300 K lower than the peak temperature near the cylinder head. These temperature differences are much larger than in piston engines and in other RCEMs reported in the literature at comparable conditions. This is because of the special design of the present layout of the machine. A relatively large difference to the adiabatic temperature can be overserved particularly at TDC. About 70 K lower temperatures were measured, which can be explained by these temperature inhomogeneities in the cylinder.