Simultaneous OH- and Formaldehyde-LIF Measurements in an HCCI Engine

Abstract

<div class="htmlview paragraph">Simultaneous OH- and formaldehyde LIF measurements have been performed in an HCCI engine using two laser sources working on 283 and 355 nm, respectively. Two ICCD camera systems, equipped with long-pass filters, were used to collect the LIF signals. The simultaneous images of OH and formaldehyde were compared with heat-release calculated from the pressure-trace matching the cycle for the LIF measurements.</div> <div class="htmlview paragraph">The measurements were performed on a 0.5 l single-cylinder optical engine equipped with port-fuel injection system. A blend of iso-octane and n-heptane was used as fuel and the compression ratio was set to 12:1. The width of the laser sheet was 40 mm and hence covered approximately half of the cylinder bore.</div> <div class="htmlview paragraph">At some 20 CAD BTDC low temperature reactions is present and formaldehyde is formed. The formaldehyde signal is then rather constant until the main heat-release starts just before TDC, where the signal decreases rapidly to low values. From some 15 CAD to 5 CAD BTDC the formaldehyde is uniformly distributed in the imaged area. As formaldehyde decreases, OH increases and follows the main rate of heat release curve, though with a slight lag in phase. Thereafter OH is formed in the areas from which the formaldehyde has disappeared and the OH signal is present to some 20 CAD ATDC.</div>