Development of a Real-Time Virtual Nitric Oxide Sensor for Light-Duty Diesel Engines

Abstract

This study describes the development of a semi-physical, real-time nitric oxide (NO) prediction model that is capable of cycle-by-cycle prediction in a light-duty diesel engine. The model utilizes the measured in-cylinder pressure and information obtained from the engine control unit (ECU). From the inputs, the model takes into account the pilot injection burning and mixing, which affects the in-cylinder mixture formation. The representative in-cylinder temperature for NO formation was determined from the mixture composition calculation. The selected temperature and mixture composition was substituted using a simplified form of the NO formation rate equation for the cycle-by-cycle estimation. The reactive area and the duration of NO formation were assumed to be limited by the fuel quantity. The model predictability was verified not only using various steady-state conditions, including the variation of the EGR rate, the boost pressure, the rail pressure, and the injection timing, but also using transient conditions, which represent the worldwide harmonized light vehicles test procedure (WLTC). The WLTC NO prediction results produced less than 3% error with the measured value. In addition, the proposed model maintained its reliability in terms of hardware aging, the changing and artificial perturbations during steady-state and transient engine operations. The model has been shown to require low computational effort because of the cycle-by-cycle, engine-out NO emission prediction and control were performed simultaneously in an embedded system for the automotive application. We expect that the developed NO prediction model can be helpful in emission calibration during the engine design stage or in the real-time controlling of the exhaust NO emission for improving fuel consumption while satisfying NO emission legislation.

Cyclic NO2:NOx ratio from a diesel engine undergoing transient load steps

“…As a result, whereas typical NO 2 levels might usually be 10% at light load, NO 2 can comprise up to 30% of total NO x 9 and in LTC up to 70%. 10 While NO x emissions can be modelled, onedimensional (1D) simulations of NO x emissions using the Zel'dovich equations have been undertaken and report accuracies of the order of 610% 11,12 having been tuned using relevant experimental data. Modelling NO 2 levels as part of total NO x in computational fluid dynamics (CFD) usually results in high levels of simulation tuning -often using fixed NO:NO 2 ratios obtained from experiments.…”

Semi-empirical estimation model of in-cylinder pressure for compression ignition engines

“…The calculation of T SOI in equation (6) comprised a number of steps. First, the temperature immediately before the first pilot injection (T pilot ) is calculated with the ideal gas assumption (equation (8)) using the incylinder pressure (P pilot ) calculated from the polytropic compression process and volume (V pilot ) at pilot injection timing.…”

“…However, there were a number of differences when estimating the ID of the first pilot because there was no combustion reaction before the first pilot is injected. Therefore, the m pilot term was omitted from equation (6) and T pilot (equation (8)) was used for the characteristic temperature in equation (6) when predicting the ID of the first pilot. The results are presented in Figure 8 and Table 3, which show the predicted ID of the first and second pilots compared to the three published ID models.…”

“…1 In-cylinder pressures were also used when modeling NOx or PM formation. 4–8 The pressure data were used primarily to calculate the heat release rate (HRR) and in-cylinder temperature in these studies. The maximum burned temperature can be derived using the maximum in-cylinder pressure to predict engine-out NO emissions.…”

“…The maximum burned temperature can be derived using the maximum in-cylinder pressure to predict engine-out NO emissions. 6 Finesso et al 7 reported that one of the dominant parameters for predicting PM emission was chemical energy release at the end of the main injection pulse, and the energy release was calculated using in-cylinder pressure data. The incylinder pressure was also used as a tool for combustion feedback control in a number of diverse studies [9][10][11] because the HRR, which offers combustion-related information (start of combustion (SOC) timing, ignition delay (ID), and the timing when specific portions of the fuel is burned) can only be practically calculated using in-cylinder pressure.…”