K. Dean Edwards

Simultaneous Low Engine-Out NOx and Particulate Matter with Highly Diluted Diesel Combustion

This paper describes the simultaneous reduction of nitrogen oxides (NOx) and particulate matter (PM) in a modern light-duty diesel engine under high exhaust gas recirculation (EGR) levels. Simultaneous reduction of NOx and PM emissions was observed under lean conditions at several low to moderate load conditions using two different approaches. The first approach utilizes a throttle to increase EGR rate beyond the maximum rate possible with sole use of the EGR valve for a particular engine condition. The second approach does not use a throttle, but rather uses a combination of EGR and manipulation of injection parameters. A significant reduction in particulate matter size and concentration was observed corresponding to the reduction in particulate mass. This PM reduction was accompanied by a significant shift in the heat release profile. In addition, there were significant cylinder-to-cylinder variations in particulate matter characteristics, gaseous emissions, and heat release. A fuel penalty is associated with operating in the low NOx and low PM regime when there are no modifications to the injection strategy. Preliminary experiments indicate that the penalty can be eliminated or reduced to a few percent while still maintaining a significant reduction in NOx and PM. An improved understanding of this combustion regime will lead to improved EGR utilization for lowering the performance requirements of post-combustion emissions controls.

Maintenance of chaos in a computational model of a thermal pulse combustor

The dynamics of a thermal pulse combustor model are examined. It is found that, as a parameter related to the fuel flow rate is varied, the combustor will undergo a transition from periodic pulsing to chaotic pulsing to a chaotic transient leading to flameout. Results from the numerical model are compared to those obtained from a laboratory-scale thermal pulse combustor. Finally the technique of maintenance (or anticontrol) of chaos is successfully applied to the model, with the result that the operation of the combustor can be continued well into the flameout regime. (c) 1997 American Institute of Physics.

Particulate Matter and Aldehyde Emissions from Idling Heavy-Duty Diesel Trucks

As part of a multi-agency study concerning emissions and fuel consumption from heavy-duty diesel truck idling, Oak Ridge National Laboratory personnel measured CO, HC, NOx, CO2, O2, particulate matter (PM), aldehyde and ketone emissions from truck idle exhaust. Two methods of quantifying PM were employed: conventional filters and a Tapered Element Oscillating Microbalance (TEOM). A partial flow micro-dilution tunnel was used to dilute the sampled exhaust to make the PM and aldehyde measurements. The work was performed at the U.S. Armys Aberdeen Test Centers (ATC) climate controlled chamber. ATC performed 37 tests on five class-8 trucks (model years ranging from 1992 to 2001). One was equipped with an 11 hp diesel auxiliary power unit (APU), and another with a diesel direct-fired heater (DFH). The APU powers electrical accessories, heating, and air conditioning, whereas a DFH heats the cab in cold weather. Both devices offer an alternative to extended truck-engine idling. Exhaust emission measurements were also made for the APU and DFH. Trucks were idled at a high and low engine speed in the following environments: 32 °C (90 °F) with cabin air conditioning on, −18 °C (0 °F) with the cabin heater on, and 18 °C (65 °F) with no accessories on. ATC test technicians adjusted the air conditioning or heater to maintain a target cabin temperature of 21 °C (70 °F). Each test was run for approximately three hours. Comparison of the results from the APU to those from the idling trucks implies that use of an APU to replace truck idling gives fuel savings (and CO2 reduction) on the order of 60-85%, 50-97% reductions in NOx, CO and HC, and PM reductions of -20% to 95%. PM emissions from the APU were higher than the “best” idling truck engine cases. The diesel-fired heater had significantly lower emissions and fuel consumption than the APU. The potential for fuel savings and environmental benefits are readily apparent. Results for PM emissions showed a wide range of emissions rates from <1 g/hr to over 20 g/hr, with the newest trucks in the 1-5 g/hr range. PM emissions generally decreased with an increase in ambient temperature and increased disproportionately with an increase in engine speed. Aldehyde mass emissions rate increased with both decreasing temperature and increasing engine speed. The mass emissions rate of regulated gaseous species generally increased with increasing engine speed. A comparison of PM measurements with the TEOM and the filter-based methods is presented.

Invited Review: A review of deterministic effects in cyclic variability of internal combustion engines

We review developments in the understanding of cycle–to–cycle variability in internal combustion engines, with a focus on spark-ignited and premixed combustion conditions. Much of the research on cyclic variability has focused on stochastic aspects, that is, features that can be modeled as inherently random with no short–term predictability. In some cases, models of this type appear to work very well at describing experimental observations, but the lack of predictability limits control options. Also, even when the statistical properties of the stochastic variations are known, it can be very difficult to discern their underlying physical causes and thus mitigate them. Some recent studies have demonstrated that under some conditions, cyclic combustion variations can have a relatively high degree of low–dimensional deterministic structure, which implies some degree of predictability and potential for real–time control. These deterministic effects are typically more pronounced near critical stability limits (e.g. near tipping points associated with ignition or flame propagation) such during highly dilute fueling or near the onset of homogeneous charge compression ignition. We review recent progress in experimental and analytical characterization of cyclic variability where low–dimensional, deterministic effects have been observed. We describe some theories about the sources of these dynamical features and discuss prospects for interactive control and improved engine designs. Taken as a whole, the research summarized here implies that the deterministic component of cyclic variability will become a pivotal issue (and potential opportunity) as engine manufacturers strive to meet aggressive emissions and fuel economy regulations in the coming decades.

A Waste Heat Recovery System for Light Duty Diesel Engines

In order to achieve proposed fuel economy requirements, engines must make better use of the available fuel energy. Regardless of how efficient the engine is, there will still be a significant fraction of the fuel energy that is rejected in the exhaust and coolant streams. One viable technology for recovering this waste heat is an Organic Rankine Cycle. This cycle heats a working fluid using these heat streams and expands the fluid through a turbine to produce shaft power. The present work was the development of such a system applied to a light duty diesel engine. This lab demonstration was designed to maximize the peak brake thermal efficiency of the engine, and the combined system achieved an efficiency of 44.4%. The design of the system is discussed, as are the experimental performance results. The system potential at typical operating conditions was evaluated to determine the practicality of installing such a system in a vehicle.

Simulating the impact of premixed charge compression ignition on light-duty diesel fuel economy and emissions of particulates and NOx

We report results from urban drive cycle simulations of a light-duty conventional vehicle and a similar hybrid electric vehicle, both of which are equipped with diesel engines capable of operating in either conventional diesel combustion mode or in premixed charge compression ignition mode. Both simulated vehicles include lean exhaust after-treatment trains for controlling hydrocarbon, carbon monoxide, nitrogen oxide, and particulate matter emissions. Our results indicate that, in the simulated conventional vehicle, premixed charge compression ignition can significantly reduce fuel consumption and emissions by reducing the need for lean nitrogen oxide traps and diesel particulate filter regeneration. However, the opportunity for utilizing premixed charge compression ignition in the simulated hybrid electric vehicle is limited because the engine typically experiences higher loads and multiple stop–start transients that are outside the allowable premixed charge compression ignition operating range. This suggests that developing ways of extending the premixed charge compression ignition operating range combined with improved control strategies for engine and emissions control management will be especially important for realizing the potential benefits of premixed charge compression ignition in hybrid electric vehicles.

Detailed Chemical Kinetic Modeling of Iso-octane SI-HCCI Transition

We describe a CHEMKIN-based multi-zone model that simulates the expected combustion variations in a single-cylinder engine fueled with iso-octane as the engine transitions from spark-ignited (SI) combustion to homogenous charge compression ignition (HCCI) combustion. The model includes a 63-species reaction mechanism and mass and energy balances for the cylinder and the exhaust flow. For this study we assumed that the SI-to-HCCI transition is implemented by means of increasing the internal exhaust gas recirculation (EGR) at constant engine speed. This transition scenario is consistent with that implemented in previously reported experimental measurements on an experimental engine equipped with variable valve actuation. We find that the model captures many of the important experimental trends, including stable SI combustion at low EGR (-0.10), a transition to highly unstable combustion at intermediate EGR, and finally stable HCCI combustion at very high EGR (-0.75). Remaining differences between the predicted and experimental instability patterns indicate that there is further room for model improvement.

A Hybrid 2-Zone/WAVE Engine Combustion Model for Simulating Combustion Instabilities During Dilute Operation

Internal combustion engines are operated under conditions of high exhaust gas recirculation (EGR) to reduce NO x emissions and promote enhanced combustion modes such as HCCI. However, high EGR under certain conditions also promotes nonlinear feedback between cycles, leading to the development of combustion instabilities and cyclic variability. We employ a two-zone phenomenological combustion model to simulate the onset of combustion instabilities under highly dilute conditions and to illustrate the impact of these instabilities on emissions and fuel efficiency. The two-zone in-cylinder combustion model is coupled to a WAVE engine-simulation code through a Simulink interface, allowing rapid simulation of several hundred successive engine cycles with many external engine parametric effects included. We demonstrate how this hybrid model can be used to study strategies for adaptive feedback control to reduce cyclic combustion instabilities and, thus, preserve fuel efficiency and reduce emissions.

Identification of Potential Efficiency Opportunities in Internal Combustion Engines Using a Detailed Thermodynamic Analysis of Engine Simulation Results

Current political and environmental concerns are driving renewed efforts to develop techniques for improving the efficiency of internal combustion engines. A detailed thermodynamic analysis of an engine and its components from a 1st and 2nd law perspective is necessary to characterize system losses and to identify efficiency opportunities. We have developed a method for performing this analysis using engine-simulation results obtained from WAVE , a commercial engine-modeling software package available from Ricardo, Inc. Results from the engine simulation are post-processed to compute thermodynamic properties such as internal energy, enthalpy, entropy, and availability (or exergy), which are required to perform energy and availability balances of the system. This analysis is performed for all major components (turbocharger, intercooler, EGR cooler, etc.) of the engine as a function of crank angle degree for the entire engine cycle. With this information, we are able to identify potential efficiency opportunities as well as guide engine experiments for exploring new technologies for recovering system losses.

Application of High Performance Computing for Simulating the Unstable Dynamics of Dilute Spark-Ignited Combustion

In collaboration with a major automotive manufacturer, we are using computational simulations of in-cylinder combustion to understand the multi-scale nonlinear physics of the dilute stability limit. Because some key features of dilute combustion can take thousands of successive cycles to develop, the computation time involved in using complex models to simulate these effects has limited industrys ability to exploit simulations in optimizing advanced engines. We describe a novel approach for utilizing parallel computations to reveal long-timescale features of dilute combustion without the need to simulate many successive engine cycles in series. Our approach relies on carefully guided, concurrent, single-cycle simulations to create metamodels that preserve the long-timescale features of interest. We use a simplified combustion model to develop and demonstrate our strategy for adaptively guiding the concurrent simulations to generate metamodels. We next will implement this strategy with higher-fidelity, multi-scale combustion models on large computing facilities to generate more refined metamodels. The refined metamodels can then be used to accelerate engine development because of their efficiency. Similar approaches might also be used for rapidly exploring the dynamics of other complex multi-scale systems that evolve with serial dependency on time.