Modeling and Control of Hydraulic Linear and Free-Piston Engines.

The EPA has developed a free-piston engine (FPE) and a hydraulic linear engine (HLE) for application as hydraulic power plants in a hydraulic hybrid vehicle. Both engines extract power from the piston motion using a linear hydraulic pump. This dissertation's objective is to compare HLE and FPE performance trends through modeling while developing the control tools necessary to enable reliable engine operation. A physics-based engine model combines dynamics, thermodynamics, and hydraulics correlations to evaluate performance trends and assist with control development. Preliminary simulations show that asymmetric piston behavior causes variations in cylinder-to-cylinder HLE efficiency that necessitate cylinder balancing. An adaptive control scheme estimates and adjusts for HLE cylinder performance discrepancies. A control-oriented model captures HLE behavior using an estimate of rotational kinetic energy sampled at the turnaround points. State feedback control ensures that the HLE tracks a set point and a recursive least squares algorithm estimates periodic differences in HLE response. An extremum seeking algorithm exploits the adaptive scheme to optimize injection timing of each cylinder individually. Precise control of piston turnaround location is paramount to reliable FPE operation. Combining an energy balance and the Otto cycle, a control-oriented model implicitly describes FPE clearance height evolution. A linearization of the control-oriented model suggests open-loop unstable operating conditions at high load. State feedback using dynamic inversion stabilizes the FPE system. In order to constrain piston motion, a reference governor manages load changes. When implemented on the physics-based model with the feedback control law, the reference governor successfully enforces a position constraint of 0.5 mm. Using the proposed control and modeling methods, a series of physics-based simulations explore HLE, FPE, and conventional engine performance. The primary difference in engine behavior is friction. While the FPE exhibits low frictional losses and the highest relative hydraulic conversion efficiency, it also suffers from a restricted power range compared to the HLE and the conventional engine due to engine speed limitations. The HLE has lower friction than the conventional engine at most operating conditions. However, inertial forces resulting from a large piston assembly mass increase HLE bearing loads and friction at high speeds.PHDMechanical EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/102345/1/kzaseck_1.pd

Development of high performance hybrid rocket fuels

In this document I discuss paraffin fuel combustion and investigate the effects of additives on paraffin entrainment and regression. In general, hybrid rockets offer an economical and safe alternative to standard liquid and solid rockets. However, slow polymeric fuel regression and low combustion efficiency have limited the commercial use of hybrid rockets. Paraffin is a fast burning fuel that has received significant attention in the 2000’s and 2010’s as a replacement for standard fuels. Paraffin regresses three to four times faster than polymeric fuels due to the entrainment of a surface melt layer. However, further regression rate enhancement over the base paraffin fuel is necessary for widespread hybrid rocket adoption. I use a small scale opposed flow burner to investigate the effect of additives on the combustion of paraffin. Standard additives such as aluminum combust above the flame zone where sufficient oxidizer levels are present. As a result no heat is generated below the flame itself. In small scale opposed burner experiments the effect of limited heat feedback is apparent. Aluminum in particular does not improve the regression of paraffin in the opposed burner. The lack of heat feedback from additive combustion limits the applicability of the opposed burner. In turn, the results obtained in the opposed burner with metal additive loaded hybrid fuels do not match results from hybrid rocket experiments. In addition, nano-scale aluminum increases melt layer viscosity and greatly slows the regression of paraffin in the opposed flow burner. However, the reactive additives improve the regression rate of paraffin in the opposed burner where standard metals do not. At 5 wt.% mechanically activated titanium and carbon (Ti-C) improves the regression rate of paraffin by 47% in the opposed burner. The mechanically activated Ti C likely reacts in or near the melt layer and provides heat feedback below the flame region that results in faster opposed burner regression. In order to examine paraffin/additive combustion in a motor environment, I conducted experiments on well characterized aluminum based additives. In particular, I investigate the influence of aluminum, unpassivated aluminum, milled aluminum/polytetrafluoroethylene (PTFE), and aluminum hydride on the performance of paraffin fuels for hybrid rocket propulsion. I use an optically accessible combustor to examine the performance of the fuel mixtures in terms of characteristic velocity efficiency and regression rate. Each combustor test consumes a 12.7 cm long, 1.9 cm diameter fuel strand under 160 kg/m 2s of oxygen at up to 1.4 MPa. The experimental results indicate that the addition of 5 wt.% 30 μm or 80 nm aluminum to paraffin increases the regression rate by approximately 15% compared to neat paraffin grains. At higher aluminum concentrations and nano-scale particles sizes, the increased melt layer viscosity causes slower regression. Alane and Al/PTFE at 12.5 wt.% increase the regression of paraffin by 21% and 32% respectively. Finally, an aging study indicates that paraffin can protect air and moisture sensitive particles from oxidation. The opposed burner and aluminum/paraffin hybrid rocket experiments show that additives can alter bulk fuel properties, such as viscosity, that regulate entrainment. The general effect of melt layer properties on the entrainment and regression rate of paraffin is not well understood. Improved understanding of how solid additives affect the properties and regression of paraffin is essential to maximize performance. In this document I investigate the effect of melt layer properties on paraffin regression using inert additives. Tests are performed in the optical cylindrical combustor at ∼1 MPa under a gaseous oxygen mass flux of ∼160 kg/m2s. The experiments indicate that the regression rate is proportional to μ0.08ρ 0.38κ0.82. In addition, I explore how to predict fuel viscosity, thermal conductivity, and density prior to testing. Mechanically activated Ti-C and Al/PTFE are examined in the optical combustor. I examine the effect of the reactivity by altering the mill time for the Ti-C and Al/PTFE particles. Mechanical activation of both Ti-C and Al/PTFE improve the regression rate of paraffin more than the unmilled additives. At 12.5 wt.% Al/PTFE milled for 40 minutes regresses 12% faster than the unmilled fuel. Similarly, at 12.5 wt.% 7.5 minute milled Ti C regresses 7% faster than unmilled Ti-C. The reactive particles increase heat transfer to the fuel surface and improve regression. The composition of the combustion products are examined using a particle catcher system in conjunction with visible light and electron microscopy. The exhaust products indicate that the mechanical activation of the Al/PTFE particles cause microexplosions that reduce exhaust particle size. However, the composition of the mechanically activated Al/PTFE products do not indicate more complete combustion. In addition, the mechanically activated and unmilled Ti-C showed no difference in exhaust products

Micron-aluminum and hydrogen peroxide propellant combustion

A desire for simple in situ propulsion spurred the development of nano-aluminum and water ice (ALICE) propellants. Hydrogen peroxide and micron-aluminum (PAL-ICE) mixtures iterate on the ALICE concept by delivering a flexible and potentially high performing propellant. This study examines the burning rate tailorability of liquid PALICE mixtures. Linear burning rates were collected using a windowed pressure vessel at 7 to 14 MPa. The investigation varied aluminum diameter from 3.00 to 35.83 μm, hydrogen peroxide (H2O2 ) concentration from 30% to 90%, and oxidizer to fuel ratio (O/F) from 1 to 1.7. Statistical analysis determined the most influential variables affecting the burning rate. Results show a large variety of burning rates, ranging from 0.5 to 4.5 cm/s at 7 MPa with power law burning rate pressure exponents ranging from 0.33 to 1.07. The statistical analysis provided a multivariate linear model for the logarithm of the burning rate with a correlation coefficient of 0.95. This model suggests aluminum diameter as the most important factor affecting the burning rate overall, and H2O2 concentration as the most in uential variable on the burning rate pressure dependence

Constrained Control of Free Piston Engine Generator based on Implicit Reference Governor

The free piston engine generator (FPEG) is a novel power plant concept for series hybrid electric vehicles (HEV) that requires reliable control to regulate piston motion and guarantee safe operation during load transitions. This paper focuses on the control and constraint enforcement in a FPEG using a reference governor. A discrete, implicit, control oriented model describing the piston motion in a two-stroke twocylinder FPEG at the turnaround point is derived based on energy balance and a feedback controller is designed to track the desired turnaround position by regulating fuel. An implicit reference governor is developed to guarantee safe piston motion by managing the load transitions. The reference governor utilizes Newton’s method applied to an implicit nonlinear model for response prediction and a bisection search algorithm to enforce the constraints for all the future time instants by adjusting the reference command. Additionally, the error in applying one iteration of Newton’s method in predicting the response of the implicit nonlinear system is estimated and accounted for in constraint tightening to guarantee that constraints are robustly enforced. The simulation results show that the feedback control scheme incorporating the developed implicit reference governor can effectively enforce the prescribed constraints during load transition.SCOPUS: ar.jinfo:eu-repo/semantics/publishe

The influence of personal protection equipment, occupant body size, and restraint system on the frontal impact responses of Hybrid III ATDs in tactical vehicles

<p><b>Objective</b>: Although advanced restraint systems, such as seat belt pretensioners and load limiters, can provide improved occupant protection in crashes, such technologies are currently not utilized in military vehicles. The design and use of military vehicles presents unique challenges to occupant safety—including differences in compartment geometry and occupant clothing and gear—that make direct application of optimal civilian restraint systems to military vehicles inappropriate. For military vehicle environments, finite element (FE) modeling can be used to assess various configurations of restraint systems and determine the optimal configuration that minimizes injury risk to the occupant. The models must, however, be validated against physical tests before implementation. The objective of this study was therefore to provide the data necessary for FE model validation by conducting sled tests using anthropomorphic test devices (ATDs). A secondary objective of this test series was to examine the influence of occupant body size (5th percentile female, 50th percentile male, and 95th percentile male), military gear (helmet/vest/tactical assault panels), seat belt type (3-point and 5-point), and advanced seat belt technologies (pretensioner and load limiter) on occupant kinematics and injury risk in frontal crashes.</p> <p><b>Methods</b>: In total, 20 frontal sled tests were conducted using a custom sled buck that was reconfigurable to represent both the driver and passenger compartments of a light tactical military vehicle. Tests were performed at a delta-V of 30 mph and a peak acceleration of 25 <i>g</i>. The sled tests used the Hybrid III 5th percentile female, 50th percentile male, and 95th percentile male ATDs outfitted with standard combat boots and advanced combat helmets. In some tests, the ATDs were outfitted with additional military gear, which included an improved outer tactical vest (IOTV), IOTV and squad automatic weapon (SAW) gunner with a tactical assault panel (TAP), or IOTV and rifleman with TAP. ATD kinematics and injury outcomes were determined for each test.</p> <p><b>Results</b>: Maximum excursions were generally greater in the 95th percentile male compared to the 50th percentile male ATD and in ATDs wearing TAP compared to ATDs without TAP. Pretensioners and load limiters were effective in decreasing excursions and injury measures, even when the ATD was outfitted in military gear.</p> <p><b>Conclusions</b>: ATD injury response and kinematics are influenced by the size of the ATD, military gear, and restraint system. This study has provided important data for validating FE models of military occupants, which can be used for design optimization of military vehicle restraint systems.</p

Constrained control of free piston engine generator based on implicit reference governor

The free piston engine generator (FPEG) is a novel power plant concept for series hybrid electric vehicles (HEV) that requires reliable control to regulate piston motion and guarantee safe operation during load transitions. This paper focuses on the control and constraint enforcement in a FPEG using a reference governor. A discrete, implicit, control oriented model describing the piston motion in a two-stroke twocylinder FPEG at the turnaround point is derived based on energy balance and a feedback controller is designed to track the desired turnaround position by regulating fuel. An implicit reference governor is developed to guarantee safe piston motion by managing the load transitions. The reference governor utilizes Newton’s method applied to an implicit nonlinear model for response prediction and a bisection search algorithm to enforce the constraints for all the future time instants by adjusting the reference command. Additionally, the error in applying one iteration of Newton’s method in predicting the response of the implicit nonlinear system is estimated and accounted for in constraint tightening to guarantee that constraints are robustly enforced. The simulation results show that the feedback control scheme incorporating the developed implicit reference governor can effectively enforce the prescribed constraints during load transition.SCOPUS: ar.jinfo:eu-repo/semantics/publishe