Eric Warren Curtis

The interaction of turbine inter-platform leakage flow with the mainstream flow

Individual nozzle guide vanes (NGV???s) in modern aeroengines are often cast as a single piece with integral hub and casing endwalls. When in operation, there is a leakage flow through the chord-wise interplatform gaps. An investigation into the effect of this leakage flow on turbine performance is presented. Efficiency measurements and NGV exit area traverse data from a low-speed research turbine are reported. Tests show that this leakage flow can have a significant impact on turbine performance, but that below a threshold leakage fraction this penalty does not rise with increasing leakage flow rate. The effect of various seal clearances are also investigated. Results from steady-state simulations using a three-dimensional multiblock Reynolds-averaged Navier-Stokes solver are presented with particular emphasis paid to the physics of the mainstream/leakage interaction and the loss generation.

Numerical Modeling and Experimental Investigations of EGR Cooler Fouling in a Diesel Engine

EGR coolers are mainly used on diesel engines to reduce intake charge temperature and thus reduce emissions of NOx and PM. Soot and hydrocarbon deposition in the EGR cooler reduces heat transfer efficiency of the cooler and increases emissions and pressure drop across the cooler. They may also be acidic and corrosive. Fouling has been always treated as an approximate factor in heat exchanger designs and it has not been modeled in detail. The aim of this paper is to look into fouling formation in an EGR cooler of a diesel engine. A 1-D model is developed to predict and calculate EGR cooler fouling amount and distribution across a concentric tube heat exchanger with a constant wall temperature. The model is compared to an experiment that is designed for correlation of the model. Effectiveness, mass deposition, and pressure drop are the parameters that have been compared. The results of the model are in a good agreement with the experimental data.

Engine Cycle Simulation of Ethanol and Gasoline Blends

Ethanol is one of many alternative transportation fuels that can be burned in internal combustion engines in the same ways as gasoline and diesel. Compared to hydrogen and electric energy, ethanol is very similar to gasoline in many aspects and can be delivered to endusers by the same infrastructures. It can be produced from biomass and is considered renewable. It is expected that the improvement in fuels over the next 20 years will be by blending biomass-based fuels with fossil fuels using existing technologies in present-day automobiles with only minor modifications, even though the overall costs of using biomass-based fuels are still considerably higher than conventional fuels. Ethanol may represent a significant alternative fuel source, especially during the transition from fossil-based fuels to more exotic power sources. Mapping engines for flexible fuel vehicles (FFV), however, would be very costly and time consuming, even with the help of model-based engine mapping (MBM). The need for using CAE (computer aided engineering) tools to reduce cost and shorten the time of engine mapping is urgent. In the present research, an ethanol model has been developed using a Ford proprietary engine CAE tool, GESIM (General Engine Simulation program) for the simulation of ethanol and ethanol-gasoline blends. GESIM was then validated against available experimental data in a 3.0L V6 2-valve engine. Results have shown that the new GESIM has successfully predicted the trends of engine burn rates, fuel consumption, exhaust temperature and various exhaust emissions for E22 and E85 fuels without any model calibrations.

Applications of CFD Modeling in GDI Engine Piston Optimization

This paper describes a CFD modeling based approach to address design challenges in GDI (gasoline direct injection) engine combustion system development. A Ford in-house developed CFD code MESIM (Multidimensional Engine Simulation) was applied to the study. Gasoline fuel is multi-component in nature and behaves very differently from the single component fuel representation under various operating conditions. A multi-component fuel model has been developed and is incorporated in MESIM code. To apply the model in engine simulations, a multi-component fuel recipe that represents the vaporization characteristics of gasoline is also developed using a numerical model that simulates the ASTM D86 fuel distillation experimental procedure. The effect of the multi-component model on the fuel air mixture preparations under different engine conditions is investigated. The modeling approach is applied to guide the GDI engine piston designs. Effects of piston designs on the fuel air mixture preparation are presented. It is found that the multi-component fuel model is critical to the accuracy of the model prediction of the fuel air preparation process, particularly under cold start conditions.

Analytical Assessment of Simplified Transient Fuel Tests for Vehicle Transient Fuel Compensation

Good air/fuel ratio (A/F) control is essential to high quality combustion performance, drivability and emissions in internal combustion engine powered vehicles. Cold start and transient fuel wall wetting effects cause significant A/F control challenges in port fuel injected (PFI) engines. Transient fuel compensation (TFC) strategies are used to help control the A/F during cold starts and transient load and RPM conditions for good vehicle performance, but developing optimum TFC strategies and calibrations in a vehicle with many competing effects is very difficult. Thus, simplified transient tests such as fuel or throttle perturbation tests are often used to develop and validate new strategies or calibrations for use in vehicle. This paper will illustrate the use of a validated physical model to analytically assess the value of fuel and throttle perturbation tests for developing a TFC calibration for vehicle use.

Modeling Transient Fuel Effects with Variable Cam Timing

The physics of the mixture preparation process plays a critical role in transient engine control, a key enabler for satisfying increasingly stringent emissions requirements. This paper presents a fully transient, coupledmodel in Modelica for the liquid fuel behavior and thermodynamic engine cycle including thermal effects for a port fuel injection engine. Details of both the liquid fuel transport and cycle simulation models are provided. The integrated model is used to examine the effects of variable cam timing on the transient fuel behavior including comparisons between simulation results and experimental data under a variety of engine operating conditions.

Numerical and experimental investigation of a compressor with active self-recirculation casing treatment for a wide operation range

A turbocharger compressor with a wide flow range and a high efficiency is important to the application of advanced clean combustion technologies, such as homogeneous charge compression ignition and low-temperature combustion, in diesel engines. Self-recirculation casing treatment is one of the techniques that can extend the compressor surge margin without much efficiency penalty. The underlying physics of the self-recirculation casing treatment technology were investigated with computational fluid dyamics modeling and bench testing in this study. It is identified that, if the bleed slot of the self-recirculation casing treatment is located upstream of the impeller passage’s throat area, self-recirculation casing treatment improves the surge margin but the throat still limits the maximum flow capacity of the compressor. On the other hand, if the bleed slot of the self-recirculation casing treatment is located at the impeller passage’s throat area, the self-recirculation casing treatment improves the maximum flow capacity but results in a significant compressor efficiency penalty in the low-flow range. An active self-recirculation casing treatment design was proposed. The active self-recirculation casing treatment design extends the compressor flow capacity and improves the surge margin without an efficiency penalty through dual bleed slots with one upstream and the other downstream of the leading edge of the splitter blades. In the choke condition, the upstream bleed slot will be closed; near the surge condition, the downstream bleed slot will be closed. In the middle flow range, both bleed slots are closed. Both the numerical data and the bench testing results show that the maximum flow rate could be extended by about 15% and the surge margin by about 20% without an efficiency penalty. The mechanism of the performance improvement is also numerically studied.

Steady State Engine Test Demonstration of Performance Improvement With an Advanced Turbocharger

Heavy EGR required on diesel engines for future emission regulation compliance has posed a big challenge to conventional turbocharger technology for high efficiency and wide operation range. This study, as part of the U.S. Department of Energy sponsored research program, is focused on advanced turbocharger technologies that can improve turbocharger efficiency on customer driving cycles while extending the operation range significantly, compared to a production turbocharger. The production turbocharger for a medium-duty truck application was selected as a donor turbo. Design optimizations were focused on the compressor impeller and turbine wheel. On the compressor side, advanced impeller design with arbitrary surface can improve the efficiency and surge margin at the low end while extending the flow capacity, while a so-called active casing treatment can provide additional operation range extension without compromising compressor efficiency. On the turbine side, mixed flow turbine technology was revisited with renewed interest due to its performance characteristics, i.e., high efficiency at low-speed ratio, relative to the base conventional radial flow turbine, which is relevant to heavy EGR operation for future diesel applications. The engine dynamometer test shows that the advanced turbocharger technology enables over 3% BSFC improvement at part-load as well as full-load condition, in addition to an increase in rated power. The performance improvement demonstrated on an engine dynamometer seems to be more than what would typically be translated from the turbocharger flow bench data, indicating that mixed flow turbine may provide additional performance benefits under pulsed exhaust flow on an internal combustion engine and in the low-speed ratio areas that are typically not covered by steady state flow bench tests.

Spray Characterization in a DISI Engine During Cold Start: (2) PDPA Investigation

Spray angle and penetration length data were taken under cold start conditions for a Direct Injection Spark Ignition engine to investigate the effect of transient conditions on spray development. The results show that during cold start, spray development depends primarily on fuel pressure, followed by Manifold Absolute Pressure (MAP). Injection frequency had little effect on spray development. The spray for this single hole, pressure-swirl fuel injector was characterized using high speed imaging. The fuel spray was characterized by three different regimes. Regime 1 comprised fuel pressures from 6 ? 13 bar, MAPs from 0.7 ? 1 bar, and was characterized by a large pre-spray along with large drop sizes. The spray angle and penetration lengths were comparatively small. Regime 2 comprised fuel pressures from 30 ? 39 bar and MAPs from 0.51 ? 0.54 bar. A large pre-spray and large drop sizes were still present but reduced compared to Regime 1. The spray angle and penetration lengths were typically larger then in Regime 1. Regime 3 comprised fuel pressures from 65 ? 102 bar and MAPs from 0.36 ? 0.46 bar. The fuel spray had a fully developed hollow cone structure with recirculation vortices at the edges of the spray, which constricted the spray angle. The spray angle was similar to Regime 2, while the penetration length increased. The pre-spray and drop size were reduced compared to Regime 2. In all regimes, decreasing MAP enlarged the spray angle, while injection frequency was not a significant factor.

Numerical investigation of the split sliding guide vane for a variable nozzle turbine

The “swing” type guide vane has been widely used to control flow capacity in variable nozzle turbines. One disadvantage of these variable nozzle turbines is the drastic drop in stage efficiency that is caused by nozzle leakage flow when the engine operates at “low-end” conditions. In the present work, a novel split sliding guide vane has been proposed to improve turbine stage performance by mitigating the nozzle leakage flow. The design idea, geometry structure, and actuating method of split sliding guide vane are described in detail. A series of steady numerical simulations were performed on both baseline and split sliding guide vane turbines to verify the effectiveness of the split sliding guide vane, at three representative nozzle openings. Simulation results indicate that split sliding guide vane can effectively improve turbine peak efficiency up to 8% at 6% nozzle opening. In addition, unsteady simulations were also carried out to investigate the interaction between rotor and nozzle, and the aerodynamic loading fluctuations on rotor blades were compared between split sliding guide vane and base model.