Matthew J. Brusstar

High Efficiency and Low Emissions from a Port-Injected Engine with Neat Alcohol Fuels

Ongoing work with methanol- and ethanol-fueled engines at the EPA’s National Vehicle and Fuel Emissions Laboratory has demonstrated improved brake thermal efficiencies over the baseline diesel engine and low steady state NOx, HC and CO, along with inherently low PM emissions. In addition, the engine is expected to have significant system cost advantages compared with a similar diesel, mainly by virtue of its low-pressure port fuel injection (PFI) system. While recognizing the considerable challenge associated with cold start, the alcohol-fueled engine nonetheless offers the advantages of being a more efficient, cleaner alternative to gasoline and diesel engines. The unique EPA engine used for this work is a turbocharged, PFI spark-ignited 1.9L, 4-cylinder engine with 19.5:1 compression ratio. The engine operates unthrottled using stoichiometric fueling from full power to near idle conditions, using exhaust gas recirculation (EGR) and intake manifold pressure to modulate engine load. As a result, the engine, operating on methanol fuel, demonstrates better than 40% brake thermal efficiency from 6.5 to 15 bar BMEP at speeds ranging from 1200 to 3500 rpm, while achieving low steady state emissions using conventional aftertreatment strategies. Similar emissions levels were realized with ethanol fuel, but with slightly higher BSFC due to reduced spark authority at this compression ratio. These characteristics make the engine attractive for hybrid vehicle applications, for which it was initially developed, yet the significant expansion of the high-efficiency islands suggest that it may have broader appeal to conventional powertrain systems. With further refinement, this clean, more efficient and less expensive alternative to today’s petroleum-based IC engines should be considered as a bridging technology to the possible future of hydrogen as a transportation fuel.

Stability, Control, and Constraint Enforcement of Piston Motion in a Hydraulic Free-Piston Engine

A free-piston engine (FPE) requires stabilizing feedback control to manage piston motion and ensure safe operation. A high-fidelity model, which simulates the FPE behavior by combining dynamic, thermodynamic, and hydraulic submodels, is exploited as an engine surrogate for control development. A control-oriented model implicitly describes the FPE piston turnaround position using energy balance principles for an idealized Otto cycle. Local eigenvalues of the control-oriented model suggest that the FPE system is open-loop unstable. The control system relies on dynamic inversion and state feedback to stabilize the plant and track a target piston turnaround position. A robust reference governor is introduced to manage load changes, such that the piston position does not violate constraints, even in the presence of parameter uncertainty. In high-fidelity simulations, the reference governor constrains piston turnaround position to ±0.5 mm of the target during a load change.

Assessing Fuel Economy From Automated Driving: Influence of Preview and Velocity Constraints

Constrained optimization control techniques with preview are designed in this paper to derive optimal velocity trajectories in longitudinal vehicle following mode, while ensuring that the gap from the lead vehicle is both safe and short enough to prevent cut-ins from other lanes. The lead vehicle associated with the Federal Test Procedures (FTP) [1] is used as an example of the achieved benefits with such controlled velocity trajectories of the following vehicle. Fuel Consumption (FC) is indirectly minimized by minimizing the accelerations and decelerations as the autonomous vehicle follows the hypothetical lead. Implementing the cost function in offline Dynamic Programming (DP) with full drive cycle preview showed up to a 17% increase in Fuel Economy (FE). Real time implementation with Model Predictive Control (MPC) showed improvements in FE, proportional to the prediction horizon. Specifically, 20s preview MPC was able to match the DP results. A minimum of 1.5s preview of the lead vehicle velocity with velocity tracking of the lead was required to obtain an increase in FE.The optimal velocity trajectory found from these algorithms exceeded the presently allowable error from standard drive cycles for FC testing. However, the trajectory was still safe and acceptable from the perspective of traffic flow. Based on our results, regulators need to consider relaxing the constant velocity error margins around the standard velocity trajectories dictated by the FTP to encourage FE increase in autonomous driving.Copyright

Use of the hypothetical lead (HL) vehicle trace: A new method for evaluating fuel consumption in automated driving

The regulation of fuel consumption and emissions around the world is based on standard drive (SD) cycles. Several autonomous or simple eco-driving methods of smoother driving and smaller acceleration and braking can violate the ± 2 MPH speed deviation regulation from the SD and hence they are currently not counted towards the vehicle fuel economy, even though they are acceptable from a traffic pattern perspective, namely following a vehicle at a safe and reasonable gap. This paper develops and suggests a prototypical vehicle velocity versus time trajectory that supersedes each SD cycle since the SD cycle is the vehicle trace from following a vehicle with the prototypical velocity trace. The prototypical velocity trace is named from now on as the Hypothetical Lead (HL) vehicle cycle. In essence, the HL cycle recreates the traffic conditions followed by the drivers of the standard drive cycles. Finally, the paper concludes with a demonstration of using the HL cycle for assessing the fuel economy benefits of autonomous following in relation to standard test cycles and limits on the following distances to ensure that the different drive traces follow the same prototypical traffic conditions in a reasonable and safe way for real world applications.

Extremum Seeking Algorithm to Optimize Fuel Injection in a Hydraulic Linear Engine

Abstract A Hydraulic Linear Engine (HLE) concept designed by the United States Environmental Protection Agency incorporates a crank for improved robustness but transmits power hydraulically Previous work has shown that each cylinder behaves differently requiring that injector timing and duration commands be managed individually in order to balance and optimize engine performance. The high-fidelity simulation summarized in this paper uses physics-based models and established correlations to predict closed-loop engine response to the reported control structures. The proposed control strategy utilizes an adaptive, cylinder-balancing algorithm to adjust fuel quantity for each cylinder and an extremum seeking algorithm to adjust fuel injection timing for each cylinder. Modeled results show an appreciable decrease in total fuel consumption using the improved injection timing.