Abstract
Pre-catalyst engine emissions and detrimental injector deposits have been widely associated with the near-nozzle fluid dynamics during and after the injection events. Although the heating and evaporation of fuel films on the nozzle surface directly affects some of these processes, there are no experimental data for the transient evolution of nozzle surface temperature during typical engine conditions. In order to address this gap in knowledge, we present a non-intrusive approach for the full-cycle time resolved measurement of the surface temperature of production nozzles in an optical engine. A mid-wave infrared high-speed camera was calibrated against controlled conditions, both out of engine and in-engine to account for non-ideal in surface emissivity and optical transmissivity. A custom-modified injector with a thermocouple embedded below the nozzle surface was used to validate the approach under running engine conditions. Calibrated infrared thermography was then applied to characterise the nozzle temperature at 1200 frames per second, during motored and fired engine operation, thus revealing for the first time the effect of transient operating conditions on the temperature of the injector nozzle’s surface.
Highlights
IntroductionPublisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations
In order to ascertain if our calibrated high-speed thermography technique would be sensitive enough to resolve small changes in injector nozzle tip temperature, we tested this approach through small changes in engine operating conditions
The uncertainties of the measurement are dependant on the clean-running and operation of the engine to minimise fouling on the optical surfaces and optimising pixel well filling which can be achieved by estimating the exposure timing for the target temperature
Summary
Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations. The accumulation of deposits in and around injector tips is associated with reduced engine performance and injector lifetime This reduction in performance is known to manifest in a variety of ways, including increased acoustic and regulated emissions [21,22,23]. Numerous methods for measuring the nozzle surface and fuel temperature have been applied, yet all methods, including the thermography technique covered here, suffer from limitations. These challenges reside in the high acquisition rates required for the largely transient temperature profiles, the extreme conditions found within a reacting engine cylinder, and the complications imposed when accessing the injector nozzle surface, both optically and physically. A summary of the key findings is presented in conclusion
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