Diesel Injector Coking: Optical-Chemical Analysis of Deposits and Influence on Injected Flow-Rate, Fuel Spray and Engine Performance

Abstract

The physical origin of injector coking in diesel engines has been clarified and the most critical design parameters and operating variables pertaining to the occurrence of the phenomenon have been identified. Fouling has been shown to be affected by many factors, such as injector temperature, nozzle configuration, hole diameter and conicity as well as fuel composition. Optical and scanning electron microscope (SFM) analyses have been conducted both inside and outside injectors of different type and four locations have been identified as the main deposition sites. Furthermore, different coking typologies, i.e., dry and wet coking, have been assessed and discussed. Energy Dispersive X-ray (EDX) spectroscopy images of the deposits on the spray hole walls have revealed that minute quantities ofZn catalyze the coking reactions to a great extent. Significant quantities ofZn have also been found in the injector deposits. An extensive experimental test campaign has been carried out at the engine test bench with different nozzle setups in order to evaluate performance deterioration after different ageing procedures. The effects of both the Zn concentration in the fuel and running time have been assessed separately on the fouling rate. Injection rate time histories have been acquired at the hydraulic test rig, under different working conditions, for both new and aged injectors. The experimental changes in the EVI profiles subsequent to fouling have been analyzed and related to the corresponding variations in engine power measured at the engine test bench. A previously developed combustion multi-zone diagnostic model has also been applied to gain a further insight into the cause and effect relationships between the experimental in-cylinder pressure time histories and engine-out emissions.

Impact on Performance, Emissions and Thermal Behavior of a New Integrated Exhaust Manifold Cylinder Head Euro 6 Diesel Engine

“…The IM engine prototype has been tested on a dynamic test bench at the Politecnico di Torino, where a complete engine instrumentation has been setup in order to characterize engine operation under steady-state and transient conditions ( [18]). The vehicle coolant circuit, which is external to the engine, was replicated and both the pipes and radiator capacities were selected as close as possible to those used in the real vehicle.…”

Exploitation of injection fusion strategies in diesel engines equipped with solenoid injectors

“…The experimental tests have been carried out on the AVL dynamic test bed, installed at the Politecnico di Torino ICE laboratories. 36,37 The test facility is equipped with a raw exhaust gas analyzer, which is made up of three analyzer trains. One of these trains has been used, in this investigation, to measure the NO x , CO, CO 2 , total HC and O 2 levels in the engine-out gases.…”

Experimental Study of the Coking Phenomenon Effects on Spray Characteristics of the High Pressure Diesel Injector

“…The deposits accumulated on injector nozzle results in partial or complete obstruction of nozzle holes, injector performance disruption, increasing injection duration (Stanly et al 2017), fuel aggregation among formed deposit layers (Zhou et al 2018) and aggravating fuel consumption (DAmbrosio and Ferrari 2012). It should be noted that, the injector nozzle deposit interaction with fuel flow through injector hole has a detrimental effect on spray characteristics discharged from injector, causing weak fuel atomization, remarkable fuel injection flow losses, incomplete combustion, emissions intensification and engine power loss (Caprotti et al 2005;Leedham et al 2004;Caprotti et al 2010).…”