Validation of a NOx estimation methodology based on the analysis of in-cylinder pressure trace

Abstract Internal combustion engines control systems are evolving rapidly in order to meet the most recent emissions standards: this process requires a deep knowledge of how the combustion process takes place, since heat-release control is crucial to manage the trade-off between engine-out emissions and best suit the tailpipe aftertreatment system operating point. Nitrogen oxides (NOx) have currently become a critical pollutant emission that needs to be limited in compression-ignited engines. Since a selective catalytic reduction (SCR) system is present in several applications, engine-out NOx concentration is a fundamental parameter to be evaluated. This work shows how an estimation of NOx concentration can be deduced from instantaneous in-cylinder pressure measurement and some of the parameters, related to the intake charge, currently available on electronic control units (ECU). A prediction model, based on Zeldovich mechanisms and Arrhenius rate of combustion is proposed, which exploits as main contributions: rate of heat release and adiabatic flame temperature. An experimental campaign (DOE) has been carried out on a diesel engine, varying the main engine control parameters, to tune the model in steady-state operating point. The predictive capability is then evaluated by feeding the model with a validation dataset in both steady state and transient condition. Finally, model response to measure uncertainties is discussed

Control-Oriented Engine Thermal Model

Abstract The optimization of modern internal combustion engines and vehicles led several researchers to investigate the effects of the coolant system on overall efficiency losses. Electric water pumps have been proposed as a solution to decrease the high power consumption that typically affects mechanically-driven water pumps at high engine speed. Furthermore, decoupling the coolant flow from engine speed allows achieving a better warm-up behavior. The coolant system components, however, also impact vehicle efficiency: the radiator area affects the overall aerodynamic drag coefficient, especially for race vehicles and motorcycles. A thermal model can be used to assess the effects of the components characteristics (pump size, efficiency, speed; radiator surface, fan size, etc.) both on the coolant system capability to reach and maintain the target temperature, and the power it requires. The same model-based approach can be used for optimal thermal management, to control the coolant system actuators (electric pump and valves, fan). The paper shows how the thermal behavior of the engine can be represented by means of a concentrated parameters model, taking into account the main coolant system components features. The model has been calibrated on a set of data referring to a high-performance motorcycle engine, including both idling and high vehicle speed conditions. The good agreement of the model output with experimental data both in static and dynamic conditions confirms that the model is able to catch a large part of the phenomena influencing the coolant temperature

Development of a Torsiometer for On-board Application☆

Abstract Modern combustion control strategies require accurate combustion control to meet the requirements for pollutant emissions reduction. Optimal combustion control can be achieved through a closed-loop control based on indicated quantities, such as engine torque and center of combustion, which can be directly calculated through a proper processing of in-cylinder pressure trace. However, on-board installation of in-cylinder pressure sensors is uncommon, mainly because it causes a significant increase in the cost of the whole engine management system. In order to overcome the problems related to the on-board installation of cylinder pressure sensors, this work presents a remote combustion sensing methodology based on the simultaneous processing of two crankshaft speed signals. To maximize the signal-to-noise ratio, each speed measurement has been performed at opposed ends of the crankshaft, i.e. in correspondence of flywheel and distribution wheel. Since an engine speed sensor, usually faced to the flywheel, is already present on-board for other control purposes, the presented approach requires that an additional speed sensor is installed. Proper processing of the signals coming from the installed speed sensors allows extracting information about crankshaft's torsional behavior. Then, the calculated instantaneous crankshaft torsion can be used to real-time estimate both torque delivered by the engine and combustion phasing within the cycle. The presented methodology has been developed and validated using a light-duty L4 Common-Rail Diesel engine mounted in a test cell at University of Bologna. However, the discussed approach is general, and can be applied to engines with a different number of cylinders, both CI and SI

model based control of intake air temperature and humidity on the test bench

Abstract Engine test benches are crucial instruments to perform tests on internal combustion engines. Possible purposes of these tests are to detect the engine performance, check the reliability of the components or make a proper calibration of engine control systems managing the actuations. Since many factors affect tests results in terms of performance, emissions and components durability, an engine test bench is equipped with several conditioning systems (oil, water and air temperature, air humidity, etc.). One of the most important systems is the HVAC (Heating, Ventilating and Air Conditioning), that is essential to control the conditions of the intake air. Intake air temperature, pressure and humidity should be controllable test parameters, because they play a key role on the combustion development. In fact, they can heavily affect the performance detected, such as power and specific consumption, and, in some cases, they may promote knock occurrence. This work presents an HVAC model-based control methodology, where each component of the air treatment system (humidifier, pre-heating and post-heating resistors, chiller and fan) is managed coupling open-loop and closed-loop controls. Each branch of the control model is composed of two parts, the first one to evaluate the target for the given HVAC component, based on the system physical model, the second one is a PID controller based on the difference between the set-point and the feedback values. The control methodology has been validated on an engine test bench where the automation system has been developed on an open software Real-Time compatible platform, allowing the integration of the HVAC control with all other functionalities concerning the test management. The paper shows the plant layout, details the control strategy and finally analyzes experimental results obtained on the test bench, highlighting the benefits of the proposed HVAC management approach

Comparison of Knock Indexes Based on CFD Analysis

Abstract Recent trends in gasoline engines, such as downsizing, downspeeding and the increase of the compression ratio make knocking combustions a serious limiting factor for engine performance. A detailed analysis of knocking events can help improving the engine performance and diagnostic strategies. An effective way is to use advanced 3D Computational Fluid Dynamics (CFD) simulation for the analysis and prediction of the combustion process. The effects of Cycle to Cycle Variation (CCV) on knocking combustions are taken into account, maintaining a \RANS\ (Reynolds Averaged Navier-Stokes) \CFD\ approach, while representing a complex running condition, where knock intensity changes from cycle to cycle. The focus of the numerical methodology is the statistical evaluation of the local air-to-fuel and turbulence distribution at the spark plugs and their correlation with the variability of the initial stages of combustion. \CFD\ simulations have been used to reproduce knock effect on the cylinder pressure trace. For this purpose, the \CFD\ model has been validated, proving its ability to predict the combustion evolution with respect to \SA\ variations, from non-knocking up to heavy knocking conditions. The pressure traces simulated by the \CFD\ model are then used to evaluate cylinder pressure-based knock indexes. Since the model is able to output other knock intensity tracers, such as the mass of fuel burned in knocking mode, or the local heat transferred to the piston, knock indexes based on the cylinder pressure trace can be related to parameters only available in a simulation environment, that are likely to be more representative of the actual knock intensity, with respect to the local pressure trace for the sensor position. The possibility of simulating hundredths of engine cycle allows using the methodology to compare the indexes quality (correlation with actual knock intensity) on a statistical base

Hybrid solar and hydrogen energy system 0-D model for off-grid sustainable power system: A case in Italy

Off-grid solar systems are one of the most promising solutions for achieving complete grid independence. Off-grid solar systems are one of the most promising solutions for achieving complete grid independence. However, the storage of large amounts of energy produced in the summer through solar panels becomes crucial However, the storage of large amounts of energy produced in the summer through solar panels becomes crucial to reach this goal and hydrogen, as a zero-CO2 energy carrier, could play a pivotal role. This paper presents a to reach this goal and hydrogen, as a zero-CO2 energy carrier, could play a pivotal role. This paper presents a case study on the integration and simulation of solar energy and hydrogen technologies in an off-grid energy case study on the integration and simulation of solar energy and hydrogen technologies in an off-grid energy plant for a teaching buildings complex in Italy. A 0-D virtual energy plant model has been developed aimed at plant for a teaching buildings complex in Italy. A 0-D virtual energy plant model has been developed aimed at estimating the net energy production and hydrogen consumption/production rates using different inputs of estimating the net energy production and hydrogen consumption/production rates using different inputs of irradiance (monthly average, daily) and energy demand (constant and variable daily consumption levels) in the irradiance (monthly average, daily) and energy demand (constant and variable daily consumption levels) in the buildings. The outcome of the analysis identifies the most convenient configuration of the plant in terms of sizing buildings. The outcome of the analysis identifies the most convenient configuration of the plant in terms of sizing and device interactions for achieving complete grid independence, and the impact of different inputs on the plant and device interactions for achieving complete grid independence, and the impact of different inputs on the plant performance. performance