In-cylinder Pressure Sensor Research Articles

Retard to the Limit: Closed-Loop COVIMEP Control for Aggressive Exhaust Heating

Abstract During cold-starts, diesel engines equipped with aftertreatment systems typically use combustion phasing retard to increase exhaust gas enthalpy to hasten catalyst light-off, resulting in lower tailpipe emissions. Although later combustion phasing can help achieve faster catalyst light-off, combustion variability increases which can physically manifest as vibration and erratic engine behavior. To achieve faster catalyst light-off while remaining within combustion variability constraints, the premise of closed-loop control of Coefficient of Variation of IMEP (COVIMEP) to a target value using feedback from an in-cylinder pressure sensor has been explored. COVIMEP controllers have been designed using a model and validated via simulation and experiment at steady-state. The simulation and experimental results indicate that closed-loop COVIMEP control is a viable technique for retarding combustion phasing to the combustion variability limit at steady-state conditions.

Piezoelectric glass-ceramic for high-temperature applications

We report on a non-ferroelectric, piezoelectric polar glass-ceramic specifically targeted for high-temperature sensor use (T > 300 °C). Potential applications include accelerometers for turbine engines and in-cylinder pressure sensors for diesel engines. Choice of an alkali-free, Sr-fresnoite (Sr2TiSi2O8) + added SiO2 bulk composition led to desirably high electrical resistivity while maintaining good piezoelectric sensitivity. Piezoelectric properties are highly competitive with existing high-temperature single crystals and ceramics, consisting of d33 = 10, d31 = 1.5, and d15 = 34 (pC/N). Support for the high value of the shear mode d15 coefficient comes from both direct measurement as well as consideration of the expected variation in effective d33 due to deviation in perfect (001) crystalline alignment, as demonstrated in this system by Wisniewski et al. (2012). Due to the low dielectric permittivity in this system (ε33T/ε0 = 11.5; ε11T/ε0 = 16.5, both at 1 kHz), the voltage coefficients are quite high: g33 = 103, g31 = 15, and g15 = 233 (×10−3 V m/N). The room-temperature pyroelectric coefficient p3 of +8 μC/m2/°C is followed by a hysteretic peak, though repeatable, near 175 °C, attaining −70 μC/m2/°C, but by 250 °C, p3 has returned to low levels and passes through zero around 275 °C. Of crucial particular importance for high-temperature applications is high electrical resistivity, well exemplified by this material, with ρ ~ 1012 Ω-cm at 300 °C and 106 at 850 °C; higher levels of resistivity can be obtained through use of raw materials with lower levels of alkali contaminants. The combination of high electrical resistivity coupled with good piezoelectric sensitivity and the lack of a Curie temperature, with its associated aging effects, makes Sr-fresnoite glass-ceramics a realistic contender in the technically-challenging field of high-temperature piezoelectric materials.

Robust fuel consumption estimation for on-line optimization of diesel engines

Accurate estimation of Brake Specific Fuel Consumption (BSFC) is required to enable on-line optimization of real-world fuel efficiency of diesel engines. This work aims to develop a BSFC estimation method which is accurate enough for an adaptive controller for on-line engine optimization, e.g., using Extremum Seeking. In this paper two different BSFC estimation methods are evaluated: A heat-release based method using in-cylinder pressure sensors and an approach based on injector opening time. Analysis of the two approaches shows that the injector opening time approach yields the highest accuracy. This method together with an adaptive controller is validated experimentally on a Euro-VI diesel engine. Experimental results show that the BSFC estimation is robust against variations in combustion phasing and scavenging losses. The estimated location, in terms of combustion phasing and scavenging losses, of the BSFC minimum remains within 0.1% relative error with respect to the measured BSFC minimum.

Predictive Pressure Control with Multiple Injections

This paper introduces a predictive combustion-engine controller for efficient fulfillment of constraints on peak pressure, exhaust temperature and NO emissions. The controller utilizes a in-cylinder pressure sensor, actuation of multiple fuel injections and numerical optimization. A physical model is used to predict pressure changes due to fuel-injection variation. The predicted pressure is used to compute changes in fuel-injection timings and durations by solving a model-predictive control problem every engine cycle. A method for separating the heat-release among different injections is presented along with a method for varying the number of injections, since the optimal number of injections varies with operating conditions. Experimental results are presented showing controller performance in the mid-load region of a Scania D13 heavy-duty engine, running on a gasoline.

A structured approach to uncertainty analysis of predictive models of engine-out NOx emissions

Predictive models of engine-out NOx emissions continue to be a topic of active research in the diesel powertrain community. Renewed interest in the use of in-cylinder pressure sensor has presented ...

In-cylinder pressure sensor–based NOx model for real-time application in diesel engines

A real-time implementable, zero-dimensional model for predicting engine-out emissions of nitrogen oxides using in-cylinder pressure measurements is developed. The model is an extension of existing works in open literature that align well with the objectives of real-time implementation. The proposed model uses a simplified Zeldovich NOx mechanism that uses combustion-related parameters derived from simplified thermodynamic and combustion sub-models. The performance of the model is discussed for both a heavy-duty and a light-duty diesel engines. The model behavior is evaluated under input uncertainty so as to provide realistic performance bounds.

Impact of injection strategy and GTL fuels on combustion process and performance under diesel engine start

The impact of three fuels (a diesel fuel without biodiesel and two Fischer Tropsch low temperature gas to liquid paraffinic fuels from natural gas) on the indicated engine performance and the timing of the combustion process under the engine start has been studied by means of cycle to cycle thermodynamic diagnosis during the first 5–6 cycles along the whole starting process. The study was carried out varying the beginning of the start of pre-injections at different thermal conditions of the engine. In all cases exhaust gas recirculation valve was closed. Both, the rate of apparent heat release and the indicated efficiency, were mainly used as comparative parameters. The work was carried out on a Nissan Qashqai light duty diesel vehicle equipped with a Kistler Kibox thermodynamic analyzer. Piezoelectric in-cylinder pressure sensors were mounted on each engine cylinder. This work demonstrates the relevance of fuel used during the engine tuning. The efficiency of GTL fuels was better when delayed strategy was tested. Compared to diesel fuel, there is potential for improving the benefits of GTL fuels on engine performance.

Engine Knock Margin Estimation Using In-Cylinder Pressure Measurements

Engine knock is among the most relevant limiting factors in the improvement of the operation of spark-ignited engines. Due to an abnormal combustion inside the cylinder chamber, it can cause performance worsening or even serious mechanical damage. Being the result of complex local chemical phenomena, knock turns out to have a significant random behavior but the increasing availability of new on-board sensors permits a deeper understanding of its mechanism. The aim of this paper is to exploit in-cylinder pressure sensors to derive a knock estimator, based on the logistic regression technique. Thanks to the proposed approach, it is possible to explicitly deal with knock random variability and to define the so-called margin (or distance ) from the knocking condition, which has been recently proven to be an effective concept for innovative knock control strategies. In a model-based estimation fashion, two modeling approaches are compared: one relies on well-known physical mechanisms while the second exploits a principal component analysis to extract relevant pressure information, thus reducing the identification effort and improving the estimation performance.

On-line statistical combustion phase optimization and control of SI gasoline engines

This paper focuses on analysis and control of the ignition timing of spark ignition (SI) engines to maximize fuel efficiency, in which the optimal reference of combustion phase and moving average based control strategy are discussed. To extract the fuel efficiency information from combustion, in-cylinder pressure sensor is available to calculate combustion phase and indicated mean effective pressure (IMEP). Then, employing CA50 as combustion phase indicator, statistical gradient descent method is utilized to seek the CA50 set point that ensures the maximum indicated fuel conversion efficiency (IFCE) and satisfies the probability constraint of incorrect adjustment with least cycles. Since the combustion suffers from cyclic variation, moving average based feedback control approach on the evaluation of consecutive in-cylinder pressure traces, is designed to track CA50 set point by adjusting spark advance. Finally, the experiments on a 6-cylinder 3.5-l SI gasoline engine validate the performance of the proposed strategies.

Combustion and Intake/Exhaust Systems Diagnosis Based on Acoustic Emissions of a GDI TC Engine

Due to increasingly stringent emission regulations and the need for more efficient powertrains, engine control systems that have been developed during the recent years have become more and more sophisticated. Obtaining accurate information about the combustion process and about all the subsystems that compose the engine can be considered key to reach the maximum overall performance. Low-cost in-cylinder pressure and turbo speed sensors are being developed, but they still present long-term reliability issues, and represent a considerable part of the entire engine management system cost. Sound emissions represent an extremely rich information source about the operating conditions of all the subsystems that comprise the entire engine. The paper shows how it is possible to extract fundamental information regarding the combustion process (such as knock and misfire), turbo speed, and air path fault at the same time, by performing an appropriate analysis of the engine acoustic emissions acquired from the very same microphone, which can thus be considered as an innovative, multifunction, and low-cost sensor for automotive applications.

Development of a Torsiometer for On-board Application

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.

Evaluation of Nonlinear Estimation Methods for Calibration of a Heat-Release Model

Model-based analysis of in-cylinder pressure sensor signals has been a key component for internal combustion engine research, diagnostics and controller development during the past decades. This analysis is often based on simple thermodynamic models of the in-cylinder processes. In order for the analysis to give accurate results, the models need to be sufficiently calibrated. This paper investigates the use of the extended Kalman filter and the particle filter for the purpose of online estimation of top-dead-center offset, a convective heat-transfer coefficient and cylinder-wall temperature in a Gatowski heat-release model. Simulation results show that the filters are consistent in estimating the true parameters, that the assumed model uncertainty and heat-release noise density works as filter tuning parameters. The filters were found to be sensitive to errors on pressure-sensor offset and the cylinder compression ratio. The filters were also evaluated against experimental data and the result showed converge times of 200 engine cycles with acceptable steady-state variance for both filters. (Less)

Accommodation Closed-loop Control of Dieseline Fueled Flexible Fuel Engine Based on In-cylinder Pressure Sensor

This paper conducts investigation on accommodation closed-loop control of dieseline fueled flexible fuel engine. In our previous work, gasoline/diesel blend ratio estimation method was proposed and acted as a feedforward controller. In this paper, power performance closed-loop control systems with or without blend ratio estimation model are simulated respectively at constant and variable load to demonstrate the necessity of feedforward controller to control system. Results show that, whether at constant or variable load, power indicators of the system with feedforward controller track the target value well. However, for system without feedforward controller, power performance deteriorates obviously, especially in variable load condition. Besides, accommodation closed-loop control system for dieseline fueled flexible fuel engine is established. The algorithm is executed by adjusting the main injection timing to seek the most economy point on the premise that the power performance of the engine can be ensured simultaneously. Compared with open-loop control algorithm, closed-loop control system is less sensitive to fuel estimation model error, which proves to be of better consistency. Moreover, the practical output torque follows the target value well and the indicated efficiency can also be optimized.

Combustion Stability Control of Dieseline PPCI Based on In-Cylinder Pressure Signals

This paper investigates on cycle-to-cycle variation of dieseline fueled PPCI engine and introduces a closed-loop control method based on in-cylinder pressure sensor. Experiments are performed on a four-cylinder compression ignition engine. Results show that pmax (maximum in-cylinder pressure) and θpmax (crank angle where pmax occurs) cannot be properly identified by the control system. Thus, COV (coefficient of variation) of pmax and θpmax cannot reflect the real combustion fluctuation level. IMEP (indicated mean effective pressure) contains information about the whole combustion process for it is calculated by all the sampled pressure of the current cycle. Therefore, COVimep can be chosen as the combustion stability indicator to evaluate cycle-to cycle variation. Besides, sweep experiments of injection timing (IT) and exhaust gas recirculation (EGR) are conducted to investigate the influence of these control parameters on COVimep and MPRR (maximum pressure rise rate). COVimep is the indicator of combustion stability while MPRR is related to the noise level. Based on detailed analysis of experimental results, a model-based combustion stability closed-loop control algorithm is proposed in order to ensure good combustion stability on the premise that the noise of engine can also be limited (which means COVimep and MPRR can be restrained below their threshold) by an acceptable level. The simulation results show that COVimep and MPRR can be restrained simultaneously under different loads.

Determining the Initial In-Cylinder Gas State Based on Semi-Physical Models

Two methodologies are presented for modeling the initial in-cylinder gas state prior to the combustion. The first method is based on measured in-cylinder pressure data and allows the cylinder individual calculation of the gas mass and temperature. A physical equation for the online calculation of the polytropic exponent during the compression stroke is derived in order to receive accurate absolute pressure data from piezo based in-cylinder pressure sensors. In order to model the in-cylinder temperature an additional semi physical model is proposed to account for the heat input during the intake stroke. From the first methodology a second semi-physical model for the average in-cylinder gas mass and temperature is derived which will only need cylinder pressure data for the calibration process of the experimental model.

Accelerometer Based Methodology for Combustion Parameters Estimation

Due to increasingly stringent emission regulations and the need of more efficient powertrains, obtaining information about combustion process becomes a key factor. Low-cost in-cylinder pressure sensors are being developed, but they still present long-term reliability issues, and represent a considerable part of the engine management system cost. Research is being conducted in order to develop methodologies for extracting relevant combustion information using standard sensors already installed on-board. The present work introduces a methodology for combustion parameters estimation, through a control-oriented analysis of structure-borne sound. The paper also shows experimental results obtained applying the estimation methodology to different passenger car engines.

Dieseline fueled flexible fuel compression ignition engine control based on in-cylinder pressure sensor

This paper conducts research on the fuel accommodation control of a fuel-flexible engine. Blended fuels from gasoline and diesel are tested on a compression ignition engine. Two problems with the fuel-flexible engine are studied. One problem is that the engine brake torque output is different with different fuels, and the other problem is that the thermal efficiency deteriorates without recalibration. One open-loop control method and one closed-loop control method based on cylinder pressure sensor are proposed to deal with the fuel accommodation control problems. The open-loop control method features fuel blend ratio detection, which is a new dimension of input for the conventional MAP based engine management system. Gasoline and diesel blend ratio detection methods are studied, and the result also provides information for the closed loop control method as a feedforward controller. An indicated mean effective pressure based method is proposed for the engine brake torque difference problem, and a feedback controller with indicated mean effective pressure maximum seeking algorithm is used to optimize engine efficiency. The fuel injection amount and timing will be adjusted according to the fuel estimation result and the feedback control algorithms. Results show that the methods proposed could identify fuel blend ratio quite accurately, the engine brake torque output could follow the target value well, and the engine thermal efficiency could be optimized.

Simultaneous Control of Combustion Timing and Ignition Delay in Multi-Cylinder Partially Premixed Combustion

In low-temperature combustion concepts such as partially premixed combustion, the ignition delay should be large enough in order to ensure sufficient fuel and air mixing before the start of combustion. It is also necessary that the combustion timing is sufficiently well phased for high thermal efficiency. Since the ignition delay and combustion timing are intimately coupled, the decoupling of these two quantities gives rise to an interesting multiple input, multiple output control problem where the control of the air system and the fuel injection system have to be combined. In a multi-cylinder engine this problem becomes underdetermined or uncontrollable with more outputs than inputs. This article investigates model-based cycle-to-cycle cylinder-individual closed-loop control of the ignition delay and the combustion phasing in a multi-cylinder heavy-duty DI engine running on a gasoline fuel mixture. The controller design of choice was model predictive control (MPC) which is a suitable design for multiple input/output systems with actuator constraints. Ignition delay and combustion phasing were extracted from cooled in-cylinder pressure sensors and controlled by manipulating injection timings, the gas mixture temperature and exhaust-gas recirculation (EGR) ratio using a dual EGR-path system and a fast thermal-management (FTM) system. (Less)

An Alternative Method to MFB50 for Combustion Phase Detection and Control in Common Rail Diesel Engines

Although injection timing does not change at every cycle in compression ignition engines, the variations in combustion phase may occur. The variations in combustion phase are directly related to emission dispersion, torque variation, and fuel economy; therefore, the variations should be minimized by combustion phase detection and control. In this study, we propose a novel combustion indicator: location of 20% of initial heat release after the peak (IHRap20) that is an alternative to MFB50 to detect and control combustion phase in real time. IHRap20 is extracted from IHR, which is a simplified heat release model derived by the product of in-cylinder volume and the gradient of difference pressure between firing pressure and motoring pressure. IHRap20 is confirmed with engine experiment that it is highly correlated to MFB50 with RMSE of 0.2790° crank angle and R <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> of 0.9873 under various operating conditions such as injection timing, mass air flow, boost pressure, and rail pressure changes. In addition, IHRap20 is able to detect combustion phase in real time with fewer number of in-cylinder pressure data and computational load compared to MFB50. Furthermore, IHRap20 is more robust to in-cylinder pressure sensor noise than MFB50. Consequently, IHRap20 is promising for real-time combustion phase detection.

Modelling of the exhaust gas recirculation rate based on the in-cylinder pressure measurement for a passenger car diesel engine

This paper proposes a modelling of the exhaust gas recirculation rate using the in-cylinder pressure sensor for a passenger car diesel engine. Traditional modelling approaches for the exhaust gas recirculation rate normally use variables which are measured for a long intake–exhaust air path so that a time delay is inevitable. In addition, the model structure is complex, since many non-linear or unmeasurable variables such as the volumetric efficiency and the efficiency of the exhaust gas recirculation cooler have to be considered in the model. The proposed exhaust gas recirculation rate model is based on the in-cylinder pressure measurement which provides instantaneous information about combustion. Therefore, when this information is used, it is able to model the exhaust gas recirculation rate with a fast response compared with traditional modelling approaches. Furthermore, the proposed model can have a simple model structure since the model does not require consideration of the non-linear or unmeasurable parameters of the air path. The proposed exhaust gas recirculation rate model was integrated into an engine control unit and validated through engine experiments on various operating conditions.