Turbocharger surge behavior for sudden valve closing downstream the compressor and effect of actuating variable nozzle turbine

Surge is an unstable phenomenon appearing when a valve closing reduces the compressor flow rate. This phenomenon is avoided for automotive turbochargers by defining a surge margin during powertrain system design. This surge margin established with measurements in steady state testing regime limits the maximal engine torque at low levels of output. An active control of the compressor could reduce the surge margin and facilitate a transient compressor operation for a short time in surge zone. In this paper, an experimental study of the transient operation of a turbocharger compressor entering the surge zone is performed. Control of the turbocharger speed is sought to avoid unsteady operation using the variable geometry turbine (VGT) nozzle actuator. From a given stable operating point, surge is induced by reducing the opening of a valve located downstream of the compressor air circuit. The effect of reducing the speed of rotation by controlling the VGT valve is investigated, as this should lead to more stable compressor operation. The rotation speed of the turbocharger is controlled to avoid an unstable operating point using servo-actuator of variable geometry turbine. From a stable operating point, the surge appearance is caused by closing a butterfly valve downstream the air circuit of the compressor. The effect on the compressor rotation speed when the opening of variable geometry turbocharger valve is modified is studied. Measurements have been conducted for different control profiles of the VGT valve placed downstream the compressor. This article presents the means used to carry out these tests as well as the results of the measurements of the instantaneous signals of pressure, temperature, flow rate and rotation speed, allowing the analysis of the surge phenomenon.

A methodology for loss and performance assessment of a variable geometry turbocharger turbine through a new meanline FORTRAN program

PurposeVariable geometry turbine (VGT), a key component of modern internal combustion engines (ICE) turbochargers, is increasingly used for better efficiency and reduced exhaust gas emissions. The aim of this study is the development of a new meanline FORTRAN code for accurate performance and loss assessment of VGTs under a wider operating range. This code is a useful alternative tool for engineers for fast design of VGT systems where higher efficiency and minimum loss are being required.Design/methodology/approachThe proposed meanline code was applied to a variable geometry mixed flow turbine at different nozzle vane angles and under a wide range of rotational speed and the expansion ratio. The numerical methodology was validated through a comparison of the predicted performance to test data. The maps of the mass flow rate as well as the efficiency of the VGT system are discussed for different nozzle vane angles under a wide range of rotational speed. Based on the developed model, a breakdown loss analysis was carried out showing a significant effect of the nozzle vane angle on the loss distribution.FindingsResults indicated that the nozzle angle of 70° has led to the maximum efficiency compared to the other investigated nozzle vane angles ranging from 30° up to 80°. The results showed that the passage loss was significantly reduced as the nozzle vane angle increases from 30° up to 70°.Originality/valueThis paper outlines a new meanline approach for variable geometry turbocharger turbines. The developed code presents the novelty of including the effect of the vane radii variation, due to the pivoting mechanism of the nozzle ring. The developed code can be generalized to either radial or mixed flow turbines with or without a VGT system.

Tailored Air-Handling System Development for Gasoline Compression Ignition in a Heavy-Duty Diesel Engine

The simultaneous application of new low-NOx emissions standards and greenhouse gas (GHG) rules has placed great pressure on the commercial vehicle industry and has driven demand for innovative solutions. One potential solution, gasoline compression ignition (GCI), utilizes gasoline’s lower reactivity to promote partially premixed combustion and extract efficiency while reducing the PM-NOx trade-off curve. Gasoline’s volatility allows for the use of higher levels of exhaust gas recirculation (EGR), a key enabler of GCI combustion. In order to deliver higher levels of EGR while maintaining sufficient boost pressure, a tailored and efficient air-handling system is critical. This work presents the analysis-led development of a low-NOx GCI air-handling system including both turbocharger matching and EGR configuration for a prototype heavy-duty GCI engine based on a model year 2013 Cummins ISX diesel engine using low octane gasoline (RON80). In the analysis-driven development process, a 1D engine system-level analysis was closely coupled with closed-cycle 3D CFD GCI combustion development. Three different boost systems were investigated using a validated 1D engine model: 1) the production turbocharger; 2) an off-the-shelf single-stage waste-gate turbocharger; 3) a prototype single-stage variable geometry turbocharger. For each boost system, three EGR configurations were evaluated: 1) a high-pressure EGR route; 2) a low-pressure EGR route; 3) a dual-loop EGR route. The air-handling system performance was first investigated over five steady-state engine operating conditions extracted from the ramped modal cycle supplemental emissions test. Then, through cosimulation using a Simulink-based engine controls model, the best performing candidates under transient operation through the Heavy-Duty Federal Test Procedure certification cycle were identified. The production turbocharger, designed for 4–6 g/kWh engine-out NOx, suffered from low combined turbocharger efficiency under the low-NOx GCI thermal boundary conditions. The prototype 1-Stage variable geometry turbocharger, when used with a high-pressure EGR configuration, demonstrated higher combined efficiencies, while the waste-gate turbocharger showed the best results when used with a dual-loop EGR system. All low-pressure only EGR configurations were found to incur additional pumping penalties due to the need for a back pressure valve to drive sufficient EGR levels. In the transient test cycle analysis, the single-stage high-pressure EGR system was capable of delivering the target boost and EGR, while the off-the-shelf waste-gate turbocharger, with its higher mass inertia, showed slower turbine response and a resulting lag in boost response. Unsurprisingly, the dual-loop EGR system also suffered from delays in EGR delivery during engine acceleration. In summary, the prototype single-stage variable geometry turbocharger with a high-pressure EGR system produced the best performance over both the steady-state and transient engine cycles and was identified as the best candidate for the prototype low-NOx heavy-duty GCI engine.

A novel variable geometry turbine achieved by elastically restrained nozzle guide vanes

Variable geometry turbocharging is one of the most significant matching methods between turbocharger and engine, and has been proven to provide air boost for entire engine speed range as well as to reduce turbo-lag. An elastically constrained device designed for a novel variable geometry turbocharger was presented in this paper. The design of the device is based on the nozzle vane’s self-adaptation under interactions of the elastic force by elastically restrained guide vane and the aerodynamic force from flowing gas. The vane rotation mechanism of the novel variable geometry turbocharger is different from regular commercial variable geometry turbocharger systems, which is achieved by an active control system (e.g. actuator). To predict the aerodynamic performance of the novel variable geometry turbocharger, the flow field of the turbine was simulated using transient computational fluid dynamics software combined with a fluid–structure interaction method. The results show that the function of elastically constrained device has similar effectiveness as the traditional variable geometry turbocharger. In addition, the efficiency of the novel variable geometry turbocharger is improved at most operating conditions. Furthermore, a turbocharged diesel engine was created using the AVL BOOST software to evaluate the benefits of the new variable geometry turbocharger. The proposed novel variable geometry turbocharger can effectively improve the engine performance at mid-high speeds, such that the maximum decrease of brake-specific fuel consumption reaches 17.91% under 100% load and 3600 r/min engine condition. However, the engine power and brake-specific fuel consumption decrease significantly at low engine speed conditions, and the decrease is more than 26% under 1000 r/min.