Max Hofmann

Laser-induced incandescence for soot diagnostics at high pressures

The influence of pressure on laser-induced incandescence (LII) is investigated systematically in premixed, laminar sooting ethylene/air flames at 1-15 bar with wavelength-, laser fluence-, and time-resolved detection. In the investigated pressure range the LII signal decay rate is proportional to pressure. This observation is consistent with the prediction of heat-transfer models in the free-molecular regime. Pressure does not systematically affect the relationship between LII signal and laser fluence. With appropriate detection timing the pressure influence on LII signals proportionality to soot volume faction obtained by extinction measurements is only minor compared with the variation observed in different flames at fixed pressures. The implications for particle sizing and soot volume fraction measurements using LII techniques at elevated pressures are discussed.

Nanoparticle formation from supersaturated carbon vapour generated by laser photolysis of carbon suboxide

Particle formation and growth from condensation of supersatd. carbon vapor was investigated. At. carbon vapor was generated under well-controlled conditions from UV-laser pulse photolysis of C3O2 at 193 nm. Particle formation and growth were studied in a wide range of conditions with varying carbon vapor concn., bath gas compn., and pressure. The formation of particulate matter was obsd. as a function of time by laser light extinction. Particle sizes were detd. in situ by time-resolved laser-induced incandescence and ex situ by transmission electronic microscopy. The characteristic time of particle growth was 20-1000 micro s. The final particle size was 5-12 nm, increased with pressure, and depends on bath gas compn. We propose a simple model for the description of carbon vapor condensation that assumes condensation of individual atoms on the cluster surface as the main growth mechanism. The comparison of expts. and simulations provides information about the initial concn. of carbon clusters for the different mixt. conditions.

NO Laser-Induced Fluorescence Imaging in the Combustion Chamber of a Spray-Guided Direct-Injection Gasoline Engine

In direct-injection gasoline (GDI) engines with charge stratification, minimizing engine-out nitrogen oxide (NO x ) emission is crucial since exh ust-gas aftertreatment tolerates only limited amounts of NO x . Reduced NO x production directly lowers the frequency of energy-inefficient catalyst regeneration cycles. In this paper we investigate NO formation in a realistic GDI engine. Quantitative in-cylinder measurements of NO concentrations are carried out via laser-induced fluorescence imaging with excitation of NO (A-X(0,2) band at 248 nm), and subsequent fluorescence detection at 220-240 nm. Engine modifications were kept to a minimum in order to provide results that are representative of practical operating conditions. Optical access via a sapphire ring enabled identical engine geometry as a production line engine. The engine is operated with commercial gasoline (Super-Plus, RON 98). Recent high-pressure spectroscopic studies of NO, O 2 and CO 2 are utilized to select an appropriate detection scheme for quantitative NO measurements under realistic conditions. CO 2 UV light absorption data is used to correct for laser and signal attenuation. NO-LIF concentrations are compared to extractive measurements using a fast gas sampling valve (GSV). NO formation is investigated at different operating conditions such as variable exhaust gas recirculation (egr).

Investigations on laser-induced incandescence (LII) for soot diagnostics at high pressure

LII has been investigated in sooting ethylene/air flames at 1 – 15 bar with wavelength-, energy-densityand time-resolved detection. LII decay coefficients increase linearly with pressure. Pressure influence on the LII intensity is limited with prompt detection. OCIS codes: (120.1740) combustion diagnostics; (300.6280) fluorescence, luminescence