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

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.

Comparative study of combustion and emissions of diesel engine fuelled with FAME and HVO

“…The intake air flow rate is measured with a mass flow meter. Using the Bosch LSU 4.2 lambda probe and the ETAS LA4 lambda sensor, the excess air coefficient (λ) is calculated with pressure compensation [13].…”

Advanced Engine Technologies for Turbochargers Solutions

“…It is well known that the turbocharger contributes to an optimized combustion process for the engine [29]. Also, the transient operation is mostly optimized in the light of response and provides the demanded torque above the maximum torque generated by a natural aspired engine [30]. The difference in time from the boosted torque and the maximum torque provided by the natural aspired engine is known as turbo-lag; this can be another problem of the turbocharger [31].…”