In-Cylinder CO2 Sampling Using Skip-Firing Method

<div class="htmlview paragraph">We propose a model of in-cylinder air mass and residual gas fraction of a turbocharged SI engine with Variable Valve Timing (VVT) actuators. VVT devices are used to produce internal exhaust gas recirculation at part load, providing beneficial effects in terms of fuel consumption and pollutant emissions. At full load, VVT actuators permit to push back knock limit by scavenging fresh air to the exhaust pipes. Modeling in-cylinder composition is an essential task for control purpose. Actually, VVT actuators affect in-cylinder fresh air charge. This has an impact on engine torque output (leading to driveability problems), and on Fuel/Air Ratio (leading to pollution peaks). In this paper, we present a model of in-cylinder air mass and residual gas fraction using only commercial-line sensors (engine speed, intake manifold pressure and VVT actuators positions). It is designed for real-time control purpose. The model does not necessitate a lot of calibration time. The proposed method consists in modeling the quantity of fresh air going through the intake valve. The model is composed of three terms. All these terms have their own physical meaning: first term gives in-cylinder total mass, second term gives the gas mass that goes through both valves during the valve overlap (either backflow of burned gas, or scavenging of fresh air), and last term models the residual gas mass staying in the cylinder from one cycle to the next one.</div>

Experimental investigation of the influence of internal and external EGR on the combustion characteristics of a controlled auto-ignition two-stroke cycle engine

Design of an H2O-LiBr absorption system using PCMs and powered by automotive exhaust gas

Misfire detection is a subject that has been deep studied during the last years and many methodologies have been developed for this purpose. Affordably detecting the misfire event and isolating the cylinder where the missing combustion took place can be considered a solved problem for engines with a limited number of cylinders. Misfire detection and in particular cylinder isolation is still challenging for engine operating conditions at very low load and high engine speed, for engines with a high number of cylinders, or when more than one misfire event is present within the same engine cycle (multiple misfire). In particular this last malfunctioning condition is very challenging, and its detection is enforced by the international regulations without requiring cylinder isolation, but only the number of misfiring cylinders. Many methodologies have been developed in the past based on the analysis of the instantaneous engine speed. The missing combustion effect on this signal is anyway very low when the number of cylinders is high and for engine operating conditions at low engine speed, giving rise to misdetection or false alarms as already mentioned. In addition when a misfire event takes place a torsional vibration is excited and shows up in the instantaneous engine speed waveform. If a multiple misfire occurs this torsional vibration is excited more than once in a very short time interval. The interaction among these successive vibrations can further generate false alarms or misdetection, and an increased complexity when dealing with cylinder isolation is necessary. The approach here presented permits enhancing existing misfire detection methods through optimized algorithm that allows correctly isolating the multiple misfiring cylinders over the entire engine operating range. This has been obtained by proper identifying the effect of the torsional vibration over the instantaneous engine speed. The identified waveform has been then used to filter out the torsional vibration effects in order to enlighten the effects of the missing combustions. In addition a proper instantaneous engine speed windowing has been introduced in order to increase the detection signal to noise ratio over the whole engine operating range. The integration of these two signal processing techniques has proven to be very effective on the engine investigated in this study, and it is easily extendible to other engine architectures. Particular care has been devoted to satisfy on-board implementation requirements in terms of memory allocation and computational power. The tests have been conducted on an L4 1.2 liter spark ignition engine mounted in a test cell. In-cylinder pressure signals have been acquired in order to validate the methodology here developed.

In this paper we analyze the nonlinear dynamic behavior of an internal exhaust gas recirculation system based on the mean-value model of an experimental engine equipped with a camshaft phaser. We develop a dynamic camshaft timing schedule that regulates the internal exhaust gas recirculation system while maintaining transient engine torque response similar to an engine with zero exhaust gas recirculation. The dynamic schedule consists of a steady-state map of the camshaft timing for optimum exhaust gas recirculation based on throttle position and engine speed, and a first order lag that regulates the transition of the camshaft timing to the optimum point. A scheme for adjusting the time constant of the first order lag depending on engine speed and throttle position is described.

A large fraction of diesel engine tailpipe NOx emissions are emitted before the aftertreatment components reach effective operating temperatures. As a result, it is essential to develop technologies to accelerate initial aftertreatment system warm-up. This study investigates the use of early exhaust valve opening (EEVO) and its combination with negative valve overlap to achieve internal exhaust gas recirculation (iEGR), for aftertreatment thermal management, both at steady state loaded idle operation and over a heavy-duty federal test procedure (HD-FTP) drive cycle. The results demonstrate that implementing EEVO with iEGR during steady state loaded idle conditions enables engine outlet temperatures above 400 °C, and when implemented over the HD-FTP, is expected to result in a 7.9% reduction in tailpipe-out NOx.

Dual fuel operation in compression ignition engines is an effective way to reduce the NOx emission. Within the certain range of fuel premixing ratio (PR), the dual fuel operation in CI-engines results in improved thermal efficiency. The dual fuel CI-engine has relatively higher cyclic variations in comparison to conventional CI-engine which limits the range of fuel premixing in dual fuel CI-engine. The cyclic variations in air-fuel ratio, cylinder wall temperature, and residual gas fraction are the major factors, which governs the variations in combustion parameters. The cyclic variations in combustion need to control for stable engine operation. The present study estimates the cyclic air-fuel ratio, cylinder wall temperature, and residual gas fraction from the measured in-cylinder pressure data of dual-fuel CI-engine. The experiments are performed on a modified single cylinder CI-engine equipped with a separate port fuel injector and its controller to operate an engine in dual fuel mode. In this study, 1500 consecutive engine cycles are recorded, and air-fuel ratio, cylinder wall temperature, and the residual gas fraction is estimated for each cycle. Pressure moment method is used to estimate the cyclic air-fuel ratio. The cyclic cylinder wall temperature is calculated by determining the inversion angle. The cyclic variations are analyzed using statistical methods.

A multi-zone Controlled Auto Ignition (CAI) model for simulating the combustion and emissions has been developed and reported in this paper. The model takes into account the effects of the boundary layer, crevice volume, and blowby. In order to investigate the influences of in-cylinder inhomogeneity, the main cylinder chamber has been divided into multiple core zones with varying temperature and composition. Mass and energy transfer between neighbouring zones were modeled. A reduced chemical kinetic mechanism was implemented in each zone to simulate the CAI combustion chemistry and emission formation. An in-house code, the LUCKS (Loughborough University Chemical Kinetics Simulation), was employed to solve the coupled differential equations of the system. The model was validated against experimental results at various Internal Exhaust Gas Recirculation (IEGR) levels and was then used to analyze the thermal and chemical effect of the IEGR on the CAI combustion. Good agreement between modeling and experimental results in terms of major CAI combustion parameters and emissions (CO, HC, and NOx) has been achieved.

<div class="htmlview paragraph">The paper describes a novel method for calculating the residual gas fraction and the trapping efficiency in a 2 stroke engine. Assuming one dimensional compressible flow through the inlet and exhaust ports, the method estimates the instantaneous mass flowing in and out from the combustion chamber; later the residual gas fraction and trapping efficiency are estimated combining together the perfect displacement and perfect mixing scavenging models. It is assumed that when the intake port opens, the fresh mixture is pushing out the burned charge without any mixing and after a multiple of the time needed for the largest eddy to perform one rotation, the two gasses are instantly mixed up together and expelled. The result is a very simple algorithm that does not require much computational time and is able to estimate with high level of precision the trapping efficiency and the residual gas fraction in 2 stroke engines. The tuning and the validation of this algorithm are performed by measuring the trapping efficiency. These measurements are conducted with an innovative technique which consists in measuring the inlet and exhaust temperature, and calculation of the blow down temperature from the pressure trace. The model was tested using a mini high speed 2 stroke HCCI engine fuelled with diethyl ether between 10,800 and 19,000 [rpm].</div>

Optimising the cam profile of an electronic unit pump for a heavy-duty diesel engine

The three main factors determining combustion efficiency in Otto engines are optimal compression pressure, effective ignition, and fuel quality. In this study, two critical variables—fuel pump pressure (38, 43, and 48 Psi) and fuel type (RON 90 and RON 92)—were analyzed to understand their impact on specific fuel consumption (SFC). An experimental research method was employed to test the effect of independent variables on dependent variables under controlled conditions. The results indicate that a fuel pump pressure of 43 Psi provides the most stable and efficient fuel consumption performance for both fuel types across the entire engine speed range. A fuel pump pressure of 38 Psi is optimal at medium engine speeds but less efficient at high speeds, whereas a pressure of 48 Psi is most efficient at low to medium speeds but decreases in efficiency at high speeds. Overall, RON 92 fuel shows an efficiency improvement over RON 90, particularly at medium to high engine speeds. The combination of a fuel pump pressure of 43 Psi and the use of RON 92 fuel is recommended to achieve optimal specific fuel consumption, as it provides consistent efficiency across various engine operating conditions.

In an effort aimed at predicting the combustion behavior of a new fuel in a conventional diesel engine, cetane (n-hexadecane) fuel was used in a military engine across the entire speed–load operating range. The ignition delay was characterized for this fuel at each operating condition. A chemical ignition delay was also predicted across the speed–load range using a detailed chemical kinetic mechanism with a constant pressure reactor model. At each operating condition, the measured in-cylinder pressure and predicted temperature at the start of injection were applied to the detailed n-hexadecane kinetic mechanism, and the chemical ignition delay was predicted without any kinetic mechanism calibration. The modeling results show that fuel–air parcels developed from the diesel spray with an equivalence ratio of 4 are the first to ignite. The chemical ignition delay results also showed decreasing igntion delays with increasing engine load and speed, just as the experimental data revealed. At lower engine speeds and loads, the kinetic modeling results show the characteristic two-stage negative temperature coefficient behavior of hydrocarbon fuels. However, at high engine speeds and loads, the reactions do not display negative temperature coefficient behavior, as the reactions proceed directly into high-temperature pathways due to higher temperatures and pressure at injection. A moderate difference between the total and chemical ignition delays was then characterized as a phyical delay period that scales inversely with engine speed. This physical delay time is representative of the diesel spray development time and is seen to become a minority fraction of the total igntion delay at higher engine speeds. The approach used in this study suggests that the ignition delay and thus start of combustion may be predicted with reasonable accuracy using kinetic modeling to determine the chemical igntion delay. Then, in conjunction with the physical delay time (experimental or modeling based), a new fuel’s acceptability in a conventional engine could be assessed by determining that the total ignition delay is not too short or too long.

The in-cylinder RGF (residual gas fraction) of internal combustion engines for new combustion concepts, such as CAI (controlled auto ignition) or HCCI (homogenous charged compression ignition), is a major parameter that affects the combustion characteristics. Thus, measurement or prediction of the cycle-by-cycle RGF and investigation into the relation between the RGF and the combustion phenomena are critical issues. However, on-line prediction of the cycle-by-cycle RGF during engine testing is not always practical due to the requirement of expensive, fast response exhaust-gas analyzers and/or theoretical models that are just too slow for application. In this study, an on-line model that can predict the RGF of each engine cycle and cylinder during the experiment in the test cell has been developed. This enhanced model can predict the in-cylinder charge conditions of each engine cycle during the test in three seconds by using the measured dynamic pressures of the intake, exhaust, and cylinder as the boundary conditions. A Fortran77 code was generated to solve the 1-D MOC (method of characteristics). This code was linked to Labview DAQ as a form of DLL (dynamic link library) to obtain three boundary pressures for each cycle. The model was verified at various speeds and valve timings under the CAI mode by comparing the results with those of the commercial code, GT-Power.

The effect of adding fusel oil to diesel on the performance and the emissions characteristics in a single cylinder CI engine

<div class="htmlview paragraph">The durability of a piston is an essential factor that limits the engine performance. The temperature of a piston, therefore, is valuable information for the development of an engine. As the conventionally applied material hardness method is not a direct measurement of temperature during operation, this method is useful only under constant-speed operating conditions and unable to satisfy various demands of piston temperature measurement. The authors have, therefore, developed the piston temperature measurement system that withstands high engine speed using the compact and light-weight electromagnetic induction method that permits direct measurements of piston temperatures with a thermistor and allows measurement information exchange near the bottom dead center. The system is applicable to motorcycle engines which often use high speed allows measurement up to 15,300 r/min and assures durability and reliability for more than 10 hours.</div> <div class="htmlview paragraph">In this report we introduce actual examples of piston temperature changes measured by the electromagnetic induction system with the typical parameters altered when the engine is operating. The phenomenon that the piston temperatures become less sensitive to changes of parameters under high engine speed conditions is thus explained by the difference in the heat transfer rate of heat input side and the heat release side.</div>