Excess Air Ratio Management in a Diesel Engine with Exhaust Backpressure Compensation.

Piotr Kasprzyk,Michał S Gęca,Arkadiusz Rybak,Maciej Mikulski,Jacek Hunicz

doi:10.3390/s20226701

Piotr Kasprzyk, Michał S Gęca + Show 3 more

Open Access

https://doi.org/10.3390/s20226701

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Abstract

The paper investigates the operation of a wideband universal exhaust gas oxygen (UEGO) sensor in a diesel engine under elevated exhaust backpressure. Although UEGO sensors provide the excess air ratio feedback signal primarily in spark ignition engines, they are also used in diesel engines to facilitate low-emission combustion. The excess air signal is used as an input for the fuel mass observer, as well as to run the engine in the low-emission regime and enable smokeless acceleration. To ensure a short response time and individual cylinder control, the UEGO sensor can be installed upstream of a turbocharger; however, this means that the exhaust gas pressure affects the measured oxygen concentration. Therefore, this study determines the sensor’s sensitivity to the exhaust pressure under typical conditions for lean burn low-emission diesel engines. Identification experiments are carried out on a supercharged single-cylinder diesel engine with an exhaust system mimicking the operation of the turbocharger. The apparent excess air measured with the UEGO sensor is compared to that obtained in a detailed exhaust gas analysis. The comparison of reference and apparent signals shows that the pressure compensation correlations used in gasoline engines do not provide the correct values for diesel engine conditions. Therefore, based on the data analysis, a new empirical formula is proposed, for which the suitability for lean burn diesel engines is verified.

Highlights

The development of a wideband universal exhaust gas oxygen (UEGO) sensor has extended the conventional application of excess air ratio (λ) signal in engine performance and emission control.The measurement principle is based on the diffusion of gasses between the so-called reference cell and pump cell governed by the yttrium-stabilized zirconia (YSZ) O2 − -conductive membrane [1]
The two previous UEGO models proposed for turbocharged spark ignition engines, i.e., Model 1 and Model 2, fail under large excess air conditions that are typical of the diesel engine operation regime
The exhaust pressure has a pronounced effect on the UEGO sensor output

Summary

Introduction

The measurement principle is based on the diffusion of gasses between the so-called reference cell and pump cell governed by the yttrium-stabilized zirconia (YSZ) O2 − -conductive membrane [1] In general terms, this diffusion rate and direction are sensitive to exhaust gas composition; wideband sensors—unlike their discrete-state predecessors—enable the measurement of λ in the whole applicable range and with fast response. This diffusion rate and direction are sensitive to exhaust gas composition; wideband sensors—unlike their discrete-state predecessors—enable the measurement of λ in the whole applicable range and with fast response Owing to their characteristics, combined with high rigidity and stability in corrosive environments, UEGO sensors are used as a standard control feature for spark ignition engines.

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