MODELING AND CONTROL OF A GASOLINE-FUELED COMPRESSION IGNITION ENGINE

This work investigates a novel combustion concept, Gasoline Compression Ignition, that derives its superiority from the high compression ratio of a compression ignition engine as well as the properties of gasoline fuel, such as longer ignition delay and higher volatility compared to diesel fuel. Gasoline Compression Ignition was experimentally tested on a 12.4L truck engine and the acquired data were leveraged to develop a physics-based 0-dimensional combustion model for an engine operating with a low-reactivity fuel. The proposed 0-dimensional combustion model was developed to account for the different stages in combustion caused by the fuel stratification of various injection events and fuel mass fractions. As the ignition delay model is an integral part of the entire combustion process and significantly affects the predictionaccuracy, special attention was paid to local phenomena influencing ignition delay. A 1-dimensional spray model by Musculus and Kattke was employed in conjunction with a Lagrangian tracking approach in order to estimate the local fuel-air ratio within the spray tip, as a proxy for reactivity. The local fuel-air ratio, in-cylinder temperature and pressure were used in an integral fashion to estimate the ignition delay. Heat release rates were modeled by using first-order non-linear differential equations. Model prediction errors in combustion phasing of less than 1 crank angle degree across most conditions were achieved. Modeling results of other combustion metrics such as combustion duration and indicated mean effective pressure are also suitably accurate. Also, the model has been shown to be capable of estimating the ringing intensity for most conditions. While the performance of the proposed model was very satisfactory, the high computational time made it unsuitable for simulations. The high computational cost was mostly caused by the 1-dimensional spray model which described the fuelstratifcation in the spray tip as a function of crank angle for multiple injection events. Insights obtained from the 1-dimensional spray model were leveraged and applied to a 0-dimensional model to reduce the computation time. With the reduced order model, the simulation time decreased by three orders of magnitude for an entire engine cycle over the combustion model with the 1-dimensional spray model. Capturing only the basic features of the spray propagation did not show a substantial increase in prediction error compared to the initially proposed model. In order for this model to reflect a virtual engine, the influence of changes in actuator settings on intake manifold dynamics was modeled with first-order transfer functions. The intake manifold dynamics in turn influence intake valve closure conditions and further the entire combustion process. The proposed model provides information about in-cylinder metrics such as combustion phasing and indicated mean effective pressure. By taking into account the losses due to gas-exchange and friction, the brake mean effective pressure was modeled. The model was also augmented to capture cycle-to-cycle variations, thereby ensuring a faithful representation of real engine behavior. The Gasoline Compression Ignition combustion model, the intake dynamics and gas-exchange and friction model as well as the cycle-to-cycle variations model were combined to create a full engine model. This Gasoline Compression Ignition engine model was used as the plant in a control system and implemented in Matlab/Simulink.The Gasoline Compression Ignition engine model was then leveraged to investigate control actions and engine behavior with and without limiting in-cylinder peak pressure as well as combustion noise. Controlling combustion noise is of particular interest for injection strategies where fuel introduction happens early in the cycle. State estimation was performed by means of a Kalman filter which feeds into a model predictive controller. The model predictive controller chooses control actions based on a predefined cost function under consideration of bounds reflecting physical constraints. The Gasoline Compression Ignition engine model was also utilized to establish a state-space model that serves the Kalman filter and model predictive controller for estimation and prediction. In addition, the proposed control architecture was investigated at two different levels of cycle-to-cycle variations. Disturbance rejection was implemented to reduce state fluctuations and control efforts when high cycle-to-cycle variations are present. The control algorithm is able to maintain the desired references for brake mean effective pressure and combustion phasing while controlling peak in-cylinder pressure and combustion noise

Influence of charge motion and compression ratio on the performance of a combustion concept employing in-cylinder gasoline and natural gas blending

Copyright © 2018 by ASME. The present paper represents a small piece of an extensive experimental effort investigating the dual-fuel operation of a light-duty spark ignited engine. Natural gas (NG) was directly injected into the cylinder and gasoline was injected into the intake-port. Direct injection (DI) of NG was used in order to overcome the power density loss usually experienced with NG port-fuel injection (PFI) as it allows an injection after intake valve closing. Having two separate fuel systems allows for a continuum of in-cylinder blend levels from pure gasoline to pure NG operation. The huge benefit of gasoline is its availability and energy density, whereas NG allows efficient operation at high load due to improved combustion phasing enabled by its higher knock resistance. Furthermore, using NG allowed a reduction of carbon dioxide emissions across the entire engine map due to the higher hydrogen-to-carbon ratio. Exhaust gas recirculation (EGR) was used to (a) increase efficiency at low and part-load operation and (b) reduce the propensity of knock at higher compression ratios (CRs) thereby enabling blend levels with greater amount of gasoline across a wider operating range. Two integral engine parameters, CR and incylinder turbulence levels, were varied in order to study their influence on efficiency, emissions, and performance over a specific speed and load range. Increasing the CR from 10.5 to 14.5 allowed an absolute increase in indicated thermal efficiency of more than 3% for 75% NG (25% gasoline) operation at 8 bar net indicated mean effective pressure (IMEP) and 2500 rpm. However, as anticipated, the achievable peak load at CR 14.5 with 100% gasoline was greatly reduced due to its lower knock resistance. The incylinder turbulence level was varied by means of tumble plates (TPs) as well as an insert for the NG injector that guides the injection spray to augment the tumble motion. The usage of TPs showed a significant increase in EGR dilution tolerance for pure gasoline operation, however, no such impact was found for blended operation of gasoline and NG

Performance, Efficiency and Emissions Assessment of Natural Gas Direct Injection compared to Gasoline and Natural Gas Port-Fuel Injection in an Automotive Engine

Interest in natural gas as a fuel for light-duty transportation has increased due to its domestic availability and lower cost relative to gasoline. Natural gas, comprised mainly of methane, has a higher knock resistance than gasoline making it advantageous for high load operation. However, the lower flame speeds of natural gas can cause ignitability issues at part-load operation leading to an increase in the initial flame development process. While port-fuel injection of natural gas can lead to a loss in power density due to the displacement of intake air, injecting natural gas directly into the cylinder can reduce such losses. A study was designed and performed to evaluate the potential of natural gas for use as a light-duty fuel. Steady-state baseline tests were performed on a single-cylinder research engine equipped for port-fuel injection of gasoline and natural gas, as well as centrally mounted direct injection of natural gas. Experimental results suggest that similar efficiencies can be achieved in part-load operation for both gasoline and natural gas. While the effects of injection timing are generally minimal for port-fuel injection, varying the injection timing for direct injection, especially after intake valve closure, can speed up the early flame development process by nearly 18°CA. Results at full-load suggest that operation with natural gas regardless of fuel system allows for an efficiency increase. While port-fuel injection of natural gas leads to a power density loss, direct injection of natural gas allows for up to a 10% improvement in full-load power density over liquid and gaseous port-fuel injection for a naturally aspirated engine. In addition to increasing full-load efficiencies, natural gas operation allows for up to a 30% reduction in engine out carbon dioxide emissions at full-load

Phantom study for comparison between computed tomography- and C-Arm computed tomography-guided puncture applied by residents in radiology

Zusammenfassung Ziel Vergleich der Punktionsabweichung und -dauer zwischen Computertomografie (CT) - und C-Arm-CT (CACT) -gesteuertem Punktionsverfahren bei Anwendung durch Assistenzarzte in Weiterbildung (AiW). Material und Methode In einer Kohorte von 25 AiW, die Teil einer wissenschaftlichen Forderung waren, wurden entweder CT- oder CACT-gesteuerte Punktionen an einem Phantom durchgefuhrt. Vor Beginn wurden der Weiterbildungsstand, die Erfahrung mit Spielen eines Musikinstruments, mit Videospielen und mit Ballsportarten und die Selbsteinschatzung von manueller Geschicklichkeit und raumlichem Denkvermogen abgefragt. Jede/r AiW fuhrte 2 Punktionen durch, wobei die 1. Punktion mit einem transaxialen bzw. einfach angulierten Nadelpfad und die 2. Punktion mit einem einfach bzw. doppelt angulierten Nadelpfad erfolgte. Punktionsabweichung und -dauer wurden zwischen den Verfahren verglichen und mit den Selbsteinschatzungen korreliert. Ergebnisse Die beiden Gruppen der AiW zeigten keine Unterschiede in der Erfahrung in der Radiologie (p = 1), in der Angiografie (p = 0.415) und in der Anzahl bereits durchgefuhrter Punktionen gesteuert durch Ultraschall (p = 0,483), CT (p = 0,934) und CACT (p = 0,466). In der CT (ohne Navigationssoftware) war die Punktionsdauer signifikant langer als mit der CACT-Bildsteuerung mit Navigationssoftware (p < 0,001). Bei der Punktionsdauer zeigten sich keine signifikanten Unterschiede zwischen der 1. und 2. Punktion im CT (p = 0,719), wahrend die 2. Punktion mit CACT schneller durchgefuhrt werden konnte (p = 0,006). Die Punktionsabweichung war weder signifikant zwischen CT- und CACT-Bildsteuerung (p = 0,337), noch zwischen der 1. und 2. Punktion der jeweiligen Verfahren (CT: p = 0,130; CACT: p = 0,391). Die Selbsteinschatzung der manuellen Geschicklichkeit korrelierte nicht mit der Punktionsabweichung (p = 0,059) und -dauer (p = 0,158). Das subjektive raumliche Denkvermogen zeigte eine moderate positive Korrelation zur Punktionsabweichung (p = 0,011), aber nicht zur -dauer (p = 0,541). Schlussfolgerung Die AiW erreichten eine dem Ausbildungsstand entsprechende, klinisch adaquate Punktionsabweichung unter CT- und CACT-Bildsteuerung. Die CACT-gesteuerten Punktionen mit Unterstutzung durch Navigationssoftware wurden schneller durchgefuhrt, und auch die Lernkurve war mit CACT-Bildsteuerung steiler. Raumliches Denkvermogen kann moglicherweise das Erlernen bildgesteuerter Punktionen beschleunigen. Kernaussagen: Die Erfahrung mit Punktionen war in einer Gruppe von AiW, die im Rahmen des Programms der Deutschen Rontgengesellschaft e. V. Forscher-fur-die-Zukunft ausgesucht wurden, dem Weiterbildungsstand entsprechend. Trotz kollektiv geringerer Erfahrung der radiologischen AiW mit der CACT-gesteuerten Punktion mit Navigationssoftwareunterstutzung ist die Lernkurve gegenuber der einfachen CT-Punktion moglicherweise steiler. Bei schwierigen Punktionswegen konnte die CACT-Bildsteuerung mit Softwareunterstutzung einen Vorteil in der Durchfuhrung gegenuber der konventionellen CT-Bildsteuerung haben. Zitierweise Meine TC, Hinrichs JB, Werncke T et al. Phantom study for comparison between computed tomography- and C-Arm computed tomography-guided puncture applied by residents in radiology. Fortschr Rontgenstr 2021; DOI: 10. 1055/a-1586-273