Identification of combustion and detonation in spark ignition engines using ion current signal

doi:10.1016/j.fuel.2018.04.080

Fuel

Volume 227, 1 September 2018, Pages 469-477

https://doi.org/10.1016/j.fuel.2018.04.080 Get rights and content

Abstract

The identification of combustion and detonation in spark ignition (SI) engines is very important to its control within optimized and efficient boundaries. While they are generally identified respectively by phase and knock sensors, this investigation provides additional evidences that the ion current could be used as a sensing device to replace those two sensors, in order to identify both phenomena. The cylinder under combustion could be determined with the ion current signal, by sampling and computing the area under the signal curve. In order to monitor detonation, the correlation between the energy of a frequency band of the ion current signal and the energy of the knock sensor signal was established. The results indicated the viability to use the ion current to detect combustion and detonation in several situations, such as variations in the fuel mixture, mileage of the spark plug, and area size of the spark plug electrode.

Introduction

Over the last decade, automakers have been incorporating new technologies on automobiles, providing better performance, energy efficiency, low pollutants, safety, and comfort. In order to increase energy efficiency and address current international legislations, new control strategies for SI engines must be developed, which require new types of sensors [1], [2]. Therefore, it is important to develop new and reliable sensors that could provide better engine diagnostics and identify several important phenomena [3]. For example, detonation could be identified by measuring pressure variations inside the combustion chamber, using a piezoelectric or an optical sensor installed inside the combustion chamber. Alternatively, it could be identified by measuring the ionization of the air/fuel mixture, also labelled as the ion current [4].

Although, an ion current sensor still presents technical challenges that prevent its commercial use, it carries a number of potential applications in automotive industry. This investigation demonstrates the feasibility of using the ion current measurement in an SI engine mounted on a real car, with the specific goal to identify the cylinder that is in combustion and the detonation phenomenon, thus replacing the functionalities of the phase and knock sensors.

Initially, we identified the variables that influence the ion current signal behavior. Then, we computed the area under that signal curve of this current, and correlated this data to the occurrence of combustion. In order to identify detonation, the harmonics of the ion current signal were analyzed and compared with the signals of the knock sensor. The results have shown the conditions in which it is possible to use the ion current sensor to identify combustion and detonation. Those results indicated that it is possible to use the ion current to replace the phase sensor signal, opening opportunities for new applications, such as identification of bad burning (misfire) and the re-ignition of the mixture that did not burn completely in previous cycles during engine operation.

This investigation is presented as follows: Sections 2 Review, 3 The ion current present an overview on recent results associated with the ion current. Section 4 shows the parameters that influence the ion current signal. Section 5 describes the sensors and data acquisition platform. Section 6 shows how the cylinder under combustion can be identified using the ion current signal, while Section 7 shows how to identify detonation with that signal, Section 8 presents an analysis of the results and, finally, Section 9 presents some concluding remarks.

Section snippets

Review

This section presented a brief review on recent investigations on the ion current in SI engine. The new Ion Current Combustion Control System (ICCS), which can control individual cylinder air fuel ratio and ignition timing, has been recently studied [5]. It has been shown that significant performance improvements could be obtained by adapting this system to a small displacement 3-cylinder engine. The characteristics of this system are: (1) to simplify the system architecture, the ignition plug

The ion current

An electric current occurs in solid, gaseous, and liquid phases. While in solids, the real current is associated to free electron carriers, for liquid and gaseous phases, current could be associated to positive and/or negative ions and/or free electrons. Therefore, the electric current that is established in electrolytic and gaseous conductors is labelled as ionic or ion current.

For the SI, the hydrocarbon burning is a chemical process that generates ions, and when subjected to an electric

Parameters that influence the ion current

A measurement of the ion current first requires a verification on all parameters that can cause disturbances, which must be compensated to provide a net value of the measured current, consistently and reliably.

Several parameters influence the ion current signal. Some authors have explored the required characteristics of a spark plug in order to allow detection of misfire, using the $U_{ion}$ [11]. Fig. 3 shows the expected signal $U_{ion}$ for combustion and misfire, along with the ignition control

Detonation sensor

The detonation can be identified by several types of measurements: with pressure sensors, installed inside the combustion chamber, or with vibration sensors, installed in the engine block.

Rotation sensor

The variable reluctance sensor is generally used to measure the engine angular position and rotation. Fig. 4 shows a variable reluctance sensor with a conditioned output signal. The phonic wheel is connected to the crankshaft and consists of a toothed wheel with 58 teeth and 2 missing ones. The missing teeth

Experimental setup

For the experimental setup, we defined the main controllable variables that allow evaluate the performance of the ion current measurements. This procedure is very important to extend such measurements to other engine conditions. The experiments have been carried out with spark plugs in two different wear conditions: new (0 km) and used (10.000 km). Additionally, two types of ignition spark plugs have been considered: Type 1 (small electrode area) and Type 2 (large electrode area). The DC

Relevant variables

In the ignition control systems, the ignition angle advance helps to reduce fuel consumption and increase the torque output. However, an excessive advance leads to detonation. In order to optimize the angular advance in commercial vehicles, ignition advance maps have been built, depending on the speed and pressure in the intake manifold, which is an indirect measurement on the mechanical load that the engine is submitted and how these variables influence $S_{ion}$ .

Experimental methodology and tests

Increasing engine angular speed

Analysis of experimental results

This section presents an overall analysis on the experimental results, and the viability of identifying the combustion and detonation using the ion current signal.

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The dispersion of $A_{ion}$ is an important information for the identification of combustion, and so far such property has not been explored in the literature;
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The amount of ethanol in gasoline is not a relevant variable, the ion current can be used to identify combustion and detonation with any of the fuel compositions considered here;
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A

Summary

This investigation has demonstrated the feasibility of using the ion current signal to identify the cylinder under combustion and detonation in a spark ignition engine, allowing replace both the phase and knock sensors. Several variables have been explored, but for practical applications, more experiments and engine conditions must be explored. Particularly, it is important to establish the optimal DC level voltage applied to the spark plug. It is also important to identify the boundaries

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Full Length ArticleIdentification of combustion and detonation in spark ignition engines using ion current signal