Thomas Michael Lavertu

An Assessment of the Relative Benefits of Miller Cycle and Turbocompounding on a Medium Speed Diesel Engine Using Second Law Analysis

The relative benefit of a power turbine as a means of exhaust energy recovery (i.e., turbocompounding) being used in conjunction with altered intake valve closure timing (Miller cycle) on a medium speed diesel engine has been investigated. An assessment of the impact of these different engine architectures on the various loss mechanisms has been performed using second law analysis. The Miller and turbocompounding cycle modification as well as the combination of the two features were studied and their relative benefits are compared and discussed. Results show the corresponding decrease in effective compression ratio achieved with Miller cycle leads to lower pre-turbine exhaust availability, which decreases the potential benefit of turbocompounding.Copyright

Estimation of PDE Performance Using a Pulsed Limit Cycle Unsteady Combustion Calculation

The objective of many research groups around the world is to establish whether Pulse Detonation Engines (PDE’s) can achieve higher operating efficiency than conventional propulsion systems (i.e., gas turbines, ramjets, etc.) In the present study, propulsive performance estimates of a pulsed limit cycle unsteady combustion calculation (PLUCC) are compared with experimental measurements and prior numeric estimates. Comparisons of the model predictions with test measurements from a three-tube experimental PDE rig. Three different configurations were compared, two with a straight tube nozzle and one with a converging nozzle. For these cases, the difference between measured and predicted thrust was within 7%. PLUCC estimates were compared to three external codes. Estimates of fuel specific impulse and specific thrust were compared at two specific Mach numbers of the flight conditions. Results are in agreement within ± 8% for each parameter, for the cases investigated. Fuel specific impulse estimates which are calculated using PLUCC are compared to the GE-GRC Q1D code and DECADE code, for a range of flight Mach numbers (0.75-3.0). The results indicated a good agreement between the codes as the estimates were within ± 6.5% for the flight speeds considered. This greatest difference in results was expected at the highest Mach number where PLUCC is most limited. However, results were more consistent between the codes at lower Mach numbers, as agreement was within 5%. Overall, the results indicate PLUCC is consistent with prior codes at estimating the propulsive performance of a PDE.

Aftertreatment System Integration on a Tier 2 Evolution Locomotive: Analysis and Field Test Results

Results of an effort to integrate an aftertreatment system for the simultaneous reduction of NOx and PM emissions on a Tier 2 Evolution Locomotive are presented. The paper provides detail on the solution that was realized to meet packaging constraints and also highlights aftertreatment performance limitations that resulted from these design decisions. Analysis results showing the predicted impact on engine performance are presented and compared to results obtained from field testing of the integrated system.Copyright

Comparison of Alternative EGR Systems for a Medium Speed Diesel Engine

Meeting future regulations for diesel engine NOx emissions with in-cylinder solutions will require a high rate of exhaust gas recirculation (EGR). For medium speed diesel engines, the exhaust manifold pressure is typically lower than that of the intake manifold, necessitating a rise in the exhaust gas pressure for exhaust flow to be introduced into the intake manifold. In this study, four high-pressure EGR engine concepts are investigated as a means to meet EPA Tier 4 NOx emissions. These concepts include a system with an EGR pump, one with a power turbine downstream of the turbocharger (i.e., turbocompounding), one with dedicated donor EGR cylinders and the use of a backpressure valve. For each system, an optimum set of parameters that included intake valve timing, intake manifold pressure, and fuel injection timing were found that satisfy the emissions requirements while staying within the mechanical limits of the system. From an efficiency perspective, the turbocompound system is generally superior, followed by the donor cylinder concept. The EGR pumping system typically has lower overall efficiency due to the compressor power requirement and the use of a backpressure valve, representing the baseline for comparison, produced the lowest system efficiency.Copyright

An Investigation in Improving the Exhaust Management Process on Miller Cycle and Turbocompounding

A reduction in diesel engine fuel consumption at a constant emissions level can be achieved by various means. A power turbine as a means of waste heat recovery (i.e., turbocompounding) and altered intake valve closure timing (Miller cycle) are two such mechanisms. Each of these technologies act as a means of improving the expansion process of the combustion gases, requiring reduced fueling for the same work extraction. When these embodiments are typically implemented, the timing of the exhaust valve opening is maintained. However, optimization of the timing of the exhaust valve opening presents the potential for further improvement in the expansion process. Variations in the exhaust valve opening timing will be investigated for Miller and turbocompounding cycles as well as the combination of the two features. Results will be shown to quantify the impact these variations have in system efficiency. Second law analysis will be used to show how these variations in engine configurations impact individual loss mechanisms. Finally, comparisons will be made to show the relative differences between Miller cycle and turbocompounding with and without optimization of the exhaust valve timing.Copyright

Limit Cycle Investigations of Pulse Detonation Combustor for Pulse Detonation Turbine Engine

A pulse limit-cycle unsteady combustion calculation (PLUCC) model has been established and used for parametric study and optimization of pulse detonation combustor (PDC) for pulse detonation turbine engine (PDTE) applications. This model considers a system consisting of an inlet plenum, an air valve, a main tube with fuel injection, a convergent nozzle, and an exit plenum. A one-step chemical reaction along with variable properties for C2H4/air is implemented in the model. Pressure and heat losses are taken into account using loss coefficients. The effects of key sizing and timing parameters, including PDC length, nozzle area ratio, operation frequency, valve open time ratio, and fuel fill time ratio, were investigated systematically. A hierarchical strategy was implemented to optimize the total pressure ratio across the PDC, while satisfying the given upstream and downstream design constraints. Nomenclature f = operation frequency ff = fill fraction L = PDC length L* = PDC reference length NAR = nozzle area ratio, combustor-to-nozzle-throat area ratio inlet p = inlet pressure (supply pressure to the inlet plenum) r t p 41 = cycle average of total pressures across PDC, inlet t r t p