Tom Stuecken

A High Speed Flow Visualization Study of Fuel Spray Pattern Effect on Mixture Formation in a Low Pressure Direct Injection Gasoline Engine

In developing a direct injection gasoline engine, the incylinder fuel air mixing is key to good performance and emissions. High speed visualization in an optically accessible single cylinder engine for direct injection gasoline engine applications is an effective tool to reveal the fuel spray pattern effect on mixture formation The fuel injectors in this study employ the unique multi-hole turbulence nozzles in a PFI-like (Port Fuel Injection) fuel system architecture specifically developed as a Low Pressure Direct Injection (LPDI) fuel injection system. In this study, three injector sprays with a narrow 40° spray angle, a 60°spray angle with 5°offset angle, and a wide 80° spray angle with 10° offset angle were evaluated. Image processing algorithms were developed to analyze the nature of in-cylinder fuel-air mixing and the extent of fuel spray impingement on the cylinder wall. Test data reveal that for a given cylinder head, piston configuration and intake air port flow characteristics, injector spray pattern plays a dominating role in how the fuel-air mixture is formed. If an appropriate injector spray pattern is chosen, the in-cylinder fuel mixing can be enhanced by minimizing fuel impingement on cylinder wall, piston top, and intake valves, thus producing a more homogeneous fuel-air mixture prior to the ignition. Engine designers can select a specific spray pattern to improve the fuel-air mixture optimized for specific parameters such as engine head, piston, valve configuration, intake air flow characteristics, fuel injection strategy, injector mounting and operating conditions.

Combustion Characteristics of a Single-Cylinder Engine Equipped with Gasoline and Ethanol Dual-Fuel Systems

The requirement of reduced emissions and improved fuel economy led the introduction of direct-injection (DI) spark-ignited (SI) engines. Dual-fuel injection system (direct-injection and port-fuel-injection (PFI)) was also used to improve engine performance at high load and speed. Ethanol is one of the several alternative transportation fuels considered for replacing fossil fuels such as gasoline and diesel. Ethanol offers high octane quality but with lower energy density than fossil fuels. This paper presents the combustion characteristics of a single cylinder dual-fuel injection SI engine with the following fueling cases: a) gasoline for PFI and DI, b) PFI gasoline and DI ethanol, and c) PFI ethanol and DI gasoline. For this study, the DI fueling portion varied from 0 to 100 percentage of the total fueling over different engine operational conditions while the engine air-to-fuel ratio remained at a constant level. It was shown in all cases that the IMEP (indicated mean effective pressure) decreases by as much as 11% as DI fueling percentage increases, except in case b) where the IMEP increases by 2% at light load. The combustion burn duration increases significantly at light load as DI fueling percentage increases, but only moderately at WOT (wide open throttle). In addition, the percentage of the ethanol in the total fueling plays a dominant role in affecting the combustion characteristics at light load; but at heavy load (WOT), the DI fueling percentage becomes an important parameter, regardless of the percentage of ethanol content in the fuel.

The Measurement and Control of Cyclic Variations of Flow in a Piston Cylinder Assembly

The existence of the cyclic variation of the flow inside an cylinder affects the performance of the engine. Developing methods to understand and control in-cylinder flow has been a goal of engine designers for nearly 100 years. In this paper, passive control of the intake flow of a 3.5-liter DaimlerChrysler engine was examined using a unique optical diagnostic technique: Molecular Tagging Velocimetry (MTV), which has been developed at Michigan State University. Probability density functions (PDFs) of the normalized circulation are calculated from instantaneous planar velocity measurements to quantify gas motion within a cylinder. Emphasis of this work is examination of methods that quantify the cyclic variability of the flow. In addition, the turbulent kinetic energy (TKE) of the flow on the tumble and swirl plane is calculated and compared to the PDF circulation results.

Burn Rate Analysis of an Ethanol-Gasoline, Dual Fueled, Spark Ignition Engine

An experimental study is performed to investigate the combustion characteristics of an ethanol-gasoline, dual fueled, single cylinder spark ignition (SI) engine. A dual fuel injection system with both Direct-Injection (DI) and Port-Fuel-Injection (PFI) is used in this work. The performance of PFI-E85 and DI-gasoline, and PFI-gasoline and DI-E85 systems is presented. E85 is a blend of 85% ethanol and 15% gasoline by volume. In each test, the percentage of E85 is varied from 100 (0% gasoline) to 0 (100% gasoline) to compare the various cases. PFI-gasoline and DI-gasoline (PFI & DI-gasoline) results are also presented to provide a baseline for comparison. The cycle-to-cycle variability is presented using coefficient of variation (COV) of indicated mean effective pressure (IMEP). Mass fraction burned (MFB) and burn duration are determined from the analysis of measured in-cylinder pressure data. The well known Rassweiler and Withrow method (Model 1), with a new linear model for the polytropic index, is used to obtain the MFB curves. The differences are presented for the net pressure method (Model 2) to evaluate the burn rates. It is found that combustion is faster with the increase in PFI percentage for all the three setups with dual fuel injection. The PFI-E85 and DI-gasoline system showed that the burn duration decreases significantly with the increase in PFI percentage; however, the PFI-gasoline and DI-E85 system showed only slight differences with the increase in PFI percentage. Model 2 showed good agreement with Model 1 at high load conditions; however, it predicts slower combustion at light load conditions.Copyright

Model Reference Adaptive Control of a Pneumatic Valve Actuator for Infinitely Variable Valve Timing and Lift

Electro-pneumatic valve actuators are used to eliminate the cam shaft of a traditional internal combustion engine. They are used to control the opening timing, duration, and lift of both intake and exhaust valves. A physics based nonlinear mathematical model called the level one model was built using Newton’s law, mass conservation and thermodynamic principles. A control oriented model, the level two model, was created by partially linearizing the level one model for model reference parameter identification. This model reduces computational throughput and enables real-time implementation. A model reference adaptive control system was used to identify the nonlinear parameters that were needed for generating a feedforward control signal. The closed-loop valve lift tracking, valve opening and closing timing control strategies were proposed. The closedloop lift control algorithm was developed and implemented in a prototype controller, and validated on a valve test bench with multiple reference valve lift set points at both 1200rpm and 5000rpm engine speeds. The experiment results showed that the actual valve lift reached the reference lift within 0.5mm of lift error in one cycle at 1200rpm and in two cycles at 5000rpm. The maximum steady state lift errors are less than 0.4mm at high valve lift and less than 1.3mm at low valve lift. Furthermore, the closed-loop valve lift control improved valve lift repeatability with more than 30% reduction of standard deviation over the open-loop control.

Effects of Pre-Injection on Combustion Characteristics of a Single-Cylinder Diesel Engine

Multiple injections used for diesel engines, especially pre- and post-injections, have the potential to reduce combustion noise and emissions with improved engine performance. This paper outlines the combustion characteristics of a single-cylinder diesel engine with multiple injections. The effects of pre-injection (multi-injection) on combustion characteristics are presented in a single-cylinder diesel engine at different engine speeds and load conditions. A common rail fuel system with a solenoid injector, driven by a peak and hold circuit, is used in this work. This enables us to control the number of injections, fuel injection timing and duration, and the fuel rail pressure that can be used to optimize the engine combustion process (e.g., eliminate engine knock). Mass fraction burned and burn durations are determined by analyzing the measured in-cylinder pressure data. Results are compared with the cases when no pre-injection was used, i.e. only main injection, at the same engine speeds and load conditions. In each study, different cases are considered with the variation in main injection timing. It is found that at full-load condition and lower engine speeds pre-injection is an effective method to alter the engine burn rate and hence to eliminate knock.Copyright

Flex Fuel Optimized SI and HCCI Engine

The central objective of the proposed work is to demonstrate an HCCI (homogeneous charge compression ignition) capable SI (spark ignited) engine that is capable of fast and smooth mode transition between SI and HCCI combustion modes. The model-based control technique was used to develop and validate the proposed control strategy for the fast and smooth combustion mode transition based upon the developed control-oriented engine; and an HCCI capable SI engine was designed and constructed using production ready two-step valve-train with electrical variable valve timing actuating system. Finally, smooth combustion mode transition was demonstrated on a metal engine within eight engine cycles. The Chrysler turbocharged 2.0L I4 direct injection engine was selected as the base engine for the project and the engine was modified to fit the two-step valve with electrical variable valve timing actuating system. To develop the model-based control strategy for stable HCCI combustion and smooth combustion mode transition between SI and HCCI combustion, a control-oriented real-time engine model was developed and implemented into the MSU HIL (hardware-in-the-loop) simulation environment. The developed model was used to study the engine actuating system requirement for the smooth and fast combustion mode transition and to develop the proposed mode transition control strategy. Finally, a single cylinder optical engine was designed and fabricated for studying the HCCI combustion characteristics. Optical engine combustion tests were conducted in both SI and HCCI combustion modes and the test results were used to calibrate the developed control-oriented engine model. Intensive GT-Power simulations were conducted to determine the optimal valve lift (high and low) and the cam phasing range. Delphi was selected to be the supplier for the two-step valve-train and Denso to be the electrical variable valve timing system supplier. A test bench was constructed to develop control strategies for the electrical variable valve timing (VVT) actuating system and satisfactory electrical VVT responses were obtained. Target engine control system was designed and fabricated at MSU for both single-cylinder optical and multi-cylinder metal engines. Finally, the developed control-oriented engine model was successfully implemented into the HIL simulation environment. The Chrysler 2.0L I4 DI engine was modified to fit the two-step vale with electrical variable valve timing actuating system. A used prototype engine was used as the base engine and the cylinder head was modified for the two-step valve with electrical VVT actuating system. Engine validation tests indicated that cylinder #3 has very high blow-by and it cannot be reduced with new pistons and rings. Due to the time constraint, it was decided to convert the four-cylinder engine into a single cylinder engine by blocking both intake and exhaust ports of the unused cylinders. The model-based combustion mode transition control algorithm was developed in the MSU HIL simulation environment and the Simulink based control strategy was implemented into the target engine controller. With both single-cylinder metal engine and control strategy ready, stable HCCI combustion was achived with COV of 2.1% Motoring tests were conducted to validate the actuator transient operations including valve lift, electrical variable valve timing, electronic throttle, multiple spark and injection controls. After the actuator operations were confirmed, 15-cycle smooth combustion mode transition from SI to HCCI combustion was achieved; and fast 8-cycle smooth combustion mode transition followed. With a fast electrical variable valve timing actuator, the number of engine cycles required for mode transition can be reduced down to five. It was also found that the combustion mode transition is sensitive to the charge air and engine coolant temperatures and regulating the corresponding temperatures to the target levels during the combustion mode transition is the key for a smooth combustion mode transition. As a summary, the proposed combustion mode transition strategy using the hybrid combustion mode that starts with the SI combustion and ends with the HCCI combustion was experimentally validated on a metal engine. The proposed model-based control approach made it possible to complete the SI-HCCI combustion mode transition within eight engine cycles utilizing the well controlled hybrid combustion mode. Without intensive control-oriented engine modeling and HIL simulation study of using the hybrid combustion mode during the mode transition, it would be impossible to validate the proposed combustion mode transition strategy in a very short period.

Electro-Pneumatic Exhaust Valve Modeling and Control for an Internal Combustion Engine

Variable valve actuation of Internal Combustion (IC) engines is capable of significantly improving their performance. It can be divided into two main categories: variable valve timing with cam shaft(s) and camless valve actuation. For camless valve actuation, research has been centered in electro-magnetic, electro-hydraulic, and electro-pneumatic valve actuators. This research studies the control of the electro-pneumatic valve actuator. The modeling and control of intake valves for the Electro-Pneumatic Valve Actuators (EPVA) was shown in early publications and this paper extends the EPVA modeling and control development to exhaust valves for the lift control which is the key to the exhaust valve control since an accurate and repeatable lift control guarantees a satisfactory valve closing timing control. Note that exhaust valve closing timing is a key parameter for controlling engine residual gas recirculation. The exhaust valve lift control challenge is the disturbance from the randomly varying in-cylinder pressure against which the exhaust valve opens. The developed strategy utilizes model based predictive techniques to overcome this disturbance. This exhaust valve lift control algorithm was validated on a 5.4 Liter 3 valve V8 engine head with a pressurized chamber to imitate the in-cylinder pressure. The experimental results demonstrated that the exhaust valve lift tracked the step reference in one cycle with the lift error under 1mm and the steady state lift error was kept below 1mm.Copyright

Active flow control for maximizing performance of spark ignited stratified charge engines. Final report

Reducing the cycle-to-cycle variability present in stratified-charge engines is an important step in the process of increasing their efficiency. As a result of this cycle-to-cycle variability, fuel injection systems are calibrated to inject more fuel than necessary, in an attempt to ensure that the engines fire on every cycle. When the cycle-to-cycle variability is lowered, the variation of work per cycle is reduced and the lean operating limit decreases, resulting in increased fuel economy. In this study an active flow control device is used to excite the intake flow of an engine at various frequencies. The goal of this excitation is to control the way in which vortices shed off of the intake valve, thus lowering the cycle-to-cycle variability in the flow field. This method of controlling flow is investigated through the use of three engines. The results of this study show that the active flow control device did help to lower the cycle-to-cycle variability of the in-cylinder flow field; however, the reduction did not translate directly into improved engine performance.

Development of an improved quantitative calibration for an exciplex liquid/vapor fuel visualization system

Exciplex-based liquid/vapor visualization systems used for fuel distribution studies allow 2D fluorescent images of the two phases to be taken separately. Although the exciplex technique is not new, an improved quantitative calibration method has been developed, relating fluorescence intensity to mass concentration of liquid and vapor fuel. Multiple droplet summation of optically thin droplets should be used to generate liquid phase calibrations for use in studies with high-pressure injectors. In addition to eliminating the need to correct for optical density, the spatial-averaging effect of this method resulted in a repeatable calibration.