Modeling of Ion Current Signal in Diesel Combustion

Abstract

Ionization in internal combustion engines produces a signal indicative of in-cylinder conditions that can be used for the feedback electronic control of the engine, to meet production goals in performance, fuel economy and emissions. Most of the research has been conducted on carbureted and port injection spark ignition engines where the ionization mechanisms are well defined. A limited number of investigations have been conducted on ionization in diesel engines because of its complex combustion process. In this study, a detailed ionization mechanism is developed and introduced in a 3-D diesel cycle simulation computational fluid dynamics (CFD) code to determine the contribution of different species in the ionization process at different engine operating conditions. The CFD code is coupled with DARS-CFD, another module used to allow chemical kinetics calculations. The three-dimensional model accounts for the heterogeneity of the charge and the resulting variations in the combustion products. Furthermore, the model shows the effects of varying fuel injection pressure and engine load on the ion current signal characteristics. Ion current traces obtained experimentally from a heavy duty diesel engine were compared to the 3-D model results. The results of the simulation indicate that some heavy hydrocarbons, soot precursors play a major role, in addition to the role of NOx in ionization in diesel combustion.

Analysis of the ion current in misfiring and firing cycles during the cold starting of a compression ignition engine

“…A centrally located MSFI (Multi Sensing Fuel Injector), another type of ion current sensor, is more global in its outreach. 37 Therefore, an MSFI should be tested to determine if it can better detect un-sustained combustion events during the cold-starting of CI engines.…”

“…34 It was also used in a Homogenous Charge Compression Ignition (HCCI) engine to improve the engine stability by controlling the combustion timing and the magnitude of peak combustion pressure. 35,36 In CI engines, the ion current signal (1) showed a correlation with soot emissions, 37 (2) could control the pilot injection duration and timing to reduce NO x and fuel consumption, and (3) could effectively adjust the combustion phasing, enabling the engine to adapt to different fuels (e.g. biodiesel, hydrotreated vegetable oil, etc., which have significantly distinct physical, and chemical properties).…”