Greg Shaver

Physically based volumetric efficiency model for diesel engines utilizing variable intake valve actuation

Advanced diesel engine architectures employing flexible valve trains enable emissions reductions and fuel economy improvements. Flexibility in the valve train allows engine designers to optimize the gas exchange process in a manner similar to how common rail fuel injection systems enable optimization of the fuel injection process. Modulating valve timings directly impacts the volumetric efficiency of the engine since it directly controls how much mass is trapped in the cylinders. In fact, it will be shown that the control authority of valve timing modulation over volumetric efficiency, that is, the range of volumetric efficiencies achievable due to modulation of the valve timing, is three times larger than the range achievable by modulation of other engine actuators such as the exhaust gas recirculation valve or the variable geometry turbocharger. Traditional empirical or regression-based models for volumetric efficiency, while suitable for conventional valve trains, are therefore challenged by flexible valve trains. The added complexity and additional empirical data needed for wide valve timing ranges limit the usefulness of these methods. A simple physically based volumetric efficiency model was developed to address these challenges. The model captures the major physical processes occurring over the intake stroke, and is applicable to both conventional and flexible intake valve trains. The model inputs include temperature and pressure in both the intake and exhaust manifolds, intake and exhaust valve event timings, engine cylinder bore, stroke, connecting rod lengths, engine speed, and effective compression ratio. The model is physically based, requires no regression tuning parameters, is generalizable to other engine platforms, and has been experimentally validated using an advanced multi-cylinder diesel engine equipped with a fully flexible variable intake valve actuation system. Experimental data were collected over a wide range of the operating space of the engine and augmented with air handling actuator and intake valve timing sweeps to maximize the range of conditions used to thoroughly experimentally validate the model for a total of 286 operating conditions. The physically based volumetric efficiency model will be shown to predict the experimentally calculated volumetric efficiency to within 5 per cent for all cases with a root mean square error of less than 2.5 per cent for the entire dataset. The physical model developed differs from previous physical modelling work through the novel application of effective compression ratio, incorporation of no tuning parameters, and extensive validation on a unique engine test bed with fully flexible intake valve actuation.

Effect of intake valve closure modulation on effective compression ratio and gas exchange in turbocharged multi-cylinder engines utilizing EGR

Advanced combustion strategies including premixed charge compression ignition, homogeneous charge compression ignition, and lifted flame combustion are promising approaches for meeting increasingly stringent emissions regulations and improving fuel efficiency in next generation powertrains. Variable valve actuation and closed-loop control promise to play a key role in the promotion and control of these advanced combustion modes. For example, modulation of intake valve closure timing dictates the effective compression ratio and influences the total amount of charge trapped inside the cylinder, and in so doing allows manipulation of the in-cylinder reactant concentrations and temperature prior to and during the combustion process. The effort described here uses data from, and an experimentally-validated simulation model for, a multi-cylinder engine with variable geometry turbocharging, cooled exhaust gas recirculation, and fully flexible variable valve actuation. This effort’s intent is to determine the control authority over the gas exchange process and effective compression ratio when intake valve closure timing modulation is included on a modern turbocharged diesel engine, as well as to lay the groundwork for closed-loop control design for the promotion and control of advanced combustion modes. The engine testbed at Purdue provides a unique opportunity to pursue these objectives for turbocharged engines with exhaust gas recirculation, as it is the only such engine system in academia outfitted with multi-cylinder fully-flexible valve actuation. A method to estimate in-cylinder temperature at top dead centre is also described. Candidate control architectures for both steady state and transient operation are introduced.

Piezoelectric Fuel Injection: Pulse-to-Pulse Coupling and Flow Rate Estimation

Improving tradeoffs between noise, fuel consumption, and emissions in future internal combustion engines will require the development of increasingly flexible fuel injection systems, which can deliver more complex injection profiles. Piezoelectric injectors have the ability to deliver multiple, tightly spaced injections in each cycle, but are highly dynamic systems requiring careful voltage input modulation to achieve sophisticated flow profiles. Closed-loop control could prove to be a key enabler for this technology, but will require online estimation of the injected fuel flow rate to be realized. This paper summarizes the development of a physics-based fuel flow estimator. Available measurements of piezo stack voltage and rail-to-injector line pressure are used for dynamic state estimation. Estimator results are compared against both open-loop simulation and experimental data for a variety of profiles at different rail pressures, and show improvement, particularly, for more complex multipulse profiles. Internal states of the estimator are used to evaluate pulse-to-pulse interaction phenomena that make control of multipulse profiles difficult to achieve. A hypothesis for pulse-to-pulse interaction is illustrated by dividing the needle lift versus fuel flow resistance relationship into regimes, and correlating the pulse-to-pulse behavior to the regime switching that occurs for tightly spaced pulses.

Physically-Based Volumetric Efficiency Model for Diesel Engines Utilizing Variable Intake Valve Actuation

Advanced diesel engine architectures employing flexible valve trains enable emissions reductions and fuel economy improvements. Flexibility in the valve train allows engine designers to optimize the gas exchange process in a manner similar to how common rail fuel injection systems enable optimization of the fuel injection process. Modulating valve timings directly impacts the volumetric efficiency of the engine. In fact, the control authority of valve timing modulation over volumetric efficiency is three times larger than that due to any other engine actuator. Traditional empirical or regression-based models for volumetric efficiency, while suitable for conventional valve trains, are therefore challenged by flexible valve trains. The added complexity and additional empirical data needed for wide valve timing ranges limit the usefulness of these methods. A physically-based volumetric efficiency model was developed to address these challenges. The model captures the major physical processes occurring over the intake stroke, and is applicable to both conventional and flexible valve trains. The model inputs include temperature and pressure in the intake and exhaust manifolds, intake and exhaust valve timings, bore, stoke, connecting rod length, engine speed and effective compression ratio, ECR. The model is physically-based, requires no regression tuning parameters, is generalizable to other engine platforms, and has been experimentally validated using an advanced multi-cylinder diesel engine equipped with a flexible variable intake valve actuation system. Experimental data was collected over a wide range of the operating space of the engine and augmented with air handling actuator and intake valve timing sweeps to maximize the range of conditions used to thoroughly experimentally validate the model for a total of 217 total operating conditions. The physical model developed differs from previous physical modeling work through the novel application of ECR, incorporation of no tuning parameters and extensive validation on unique engine test bed with flexible intake valve actuation.Copyright

Fuel-efficient exhaust thermal management using cylinder throttling via intake valve closing timing modulation:

Most diesel engines meet today’s strict NOx and particulate matter emission regulations using after-treatment systems. A major drawback of these after-treatment systems is that they are efficient in reducing emissions only when their catalyst temperature is within a certain range (typically between 250  °C and 450 °C). At lower engine loads this is a major problem as the exhaust temperatures are usually below 250 °C. The primary objective of this study was to analyze “cylinder throttling” via both delayed and advanced intake valve closure timing. The effect of cylinder throttling on exhaust gas temperatures, fuel consumption, in-cylinder combustion and emissions is outlined. A significant increase in turbine outlet temperature accompanied by a decrease in fuel consumption, NOx, and particulate matter emissions was observed. Both delayed and advanced intake valve closure timings were equally effective. The increase in exhaust gas temperatures was attributed to a drop in air flow through the engine, which resulted from a reduction in the volumetric efficiency via cylinder throttling. The increase in fuel efficiency resulted from a decrease in the pumping work through a reduction in air flow through the engine. Reductions in NOx are attributed to the combined effect of a lower in-cylinder temperature due to a reduction in piston-motion-induced compression and a shift to a more premixed combustion mode. Particulate matter emissions were also reduced as a result of additional premixing. At the 1200 RPM and 2.5 bar brake mean effective pressure (BMEP) operating point, both delayed and advanced intake valve closure timings resulted in a turbine outlet temperature increase from 195 °C to 255 °C accompanied by an increase in brake thermal efficiency of 1.5% (absolute) and a reduction in brake-specific NOx and particulate matter emissions by 40% and 30%, respectively.

Control-variable-based accommodation of biodiesel blends

This paper introduces, and presents experimental validation for, an on-engine applicable control framework for fuel-flexible combustion of diesel–biodiesel blends. The approach is based on changing two of the closed-loop targeted control variables used by the engine control module (ECM): (1) replacing exhaust gas recirculation (EGR) fraction with combustible oxygen mass fraction (COMF); (2) replacing total injected fuel mass with total injected fuel energy, including replacing start of main injection timing with end of main injection timing. It is shown that the stock ECM control structure with pure biodiesel (B100) produces 38 per cent more brake-specific nitrogen oxides (NO x ) compared to pure conventional diesel (B0). However, new results presented here with the proposed control framework show that B100 can be made to produce lower brake-specific NO x , 2 per cent higher brake thermal efficiency, 50 per cent lower brake-specific particulate matter, and 1.2 dB lower combustion noise than B0. Benefits of, and novel contributions related to, this strategy are that it is generalizable to other engine systems, is physically based, does not require modified or additional engine calibration, and maintains the stock B0 performance. In essence, the approach presented defines the biodiesel blend control problem as closed-loop targeting of COMF and injected fuel energy, paving the way for future work in controller design to achieve these targets in real-time, on-engine situations.

Turbocharger Map Reduction for Control-Oriented Modeling

The gas exchange process in a modern diesel engine is generally modeled using manufacturer-provided performance maps that describe mass flows through, and efficiencies of, the turbine and compressor. These maps are typically implemented as look-up tables requiring multiple interpolations based on pressure ratios across the turbine and compressor, as well as the turbocharger shaft speed. In the case of variable-geometry turbochargers, the nozzle position is also an input to these maps. This method of interpolating or extrapolating data is undesirable when modeling for estimation and control, and though there have been several previous efforts to reduce dependence on turbomachinery maps, many of these approaches are complex and not easily implemented in engine control systems. As such, the aim of this paper is to reduce turbocharger maps to analytical functions for models amenable to estimation and control.Copyright

Oil Accumulation and First Fire Readiness Analysis of Cylinder Deactivation

Cylinder deactivation (CDA) is a technology that can improve the fuel economy and exhaust thermal management of compression ignition engines (diesel and natural gas), especially at low loads and engine idling conditions. The reduction in engine displacement during CDA improves fuel efficiency at low loads primarily through a reduction in pumping work. During deactivation of a given cylinder the drop in pres- sure inside the cylinder could possibly lead to the transport of oil from the crankcase into the cylinder owing to the reduced pressure difference between the crankcase and the cylinder. In addition, cylinder deactivation might inhibit the first fire readiness of a reactivating cylinder as a result of reduced wall, head, and piston temperatures. Both of these potential issues are quantitatively studied in this paper. This paper describes a strategy to estimate in-cylinder oil accumulation during CDA, and first fire readiness following CDA, through comparison of individual heat realease profiles before and after CDA. Cylinder cool-down and oil accumulation dur- ing deactivation could possibly result in misfire or degraded combustion upon an at- tempt to reactivate a given cylinder. Fortunately, experiments described in this paper demonstrate no cases of misfire at any speed/load conditions for the CDA durations tested, specifically, 100 ft-lb load at 800 rpm and 1200 rpm with deactivation intervals of 0.5, 5, 10 and 20 minutes. Although pilot heat release in the reactivated cylinders was delayed by approximately 1 CAD after 5 minutes of CDA, the main heat release was very similar to the heat release of a continuously activated cylinder. As such, results show no first fire readiness issues at the conditions tested. The duration of time the engine could be operated in CDA mode without significant oil accumulation, and other methods to minimize oil accumulation during CDA have also been proposed.

Physics Based Control Oriented Modeling of Exhaust Gas Enthalpy for Engines Utilizing Variable Valve Actuation

Accurate calculation of the conditions (i.e., temperature, pressure, and enthalpy) of internal combustion engine cylinder exhaust is critical to the modeling of, and control design development for, gas exchange in modern and future diesel engine systems. In this paper, a physically-based model for cylinder exhaust temperature, pressure, and enthalpy for engines equipped with variable valve actuation is outlined and extensively validated against experimental data from 193 operating points. The model takes the known conditions when the intake valves close and steps through a polytropic compression process, constant pressure combustion process beginning at top-dead center, and a polytropic expansion process to achieve the desired results when the exhaust valves open. To incorporate the flexibility of modulating the intake valve opening and closing, the effective compression ratio is used to establish the conditions when the intake valves close. Experimental model validation, via a unique multi-cylinder diesel engine utilizing fully flexible intake valve actuation, shows that the model captures the influences of all of the model inputs: engine speed, charge flow, total fueling quantity, intake manifold pressure, and effective compression ratio.Copyright

Control Design Amenable Model of Needle Position for a Direct Acting Piezoelectric Fuel Injector

Piezo electric injectors provide a means to lower emissions, noise and fuel consumption in advanced IC engines, by providing the capability to allow for tightly spaced injections and rate shaping. With a focus on generating a control design amenable model capturing the injector needle dynamics, the effort described here includes a model simplification and reduction strategy of an experimentally validated, physics-based 13 state model of a direct acting piezo electric injector. The resulting reduced order model for needle dynamics is validated for both single and multi pulse conditions.Copyright