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One-dimensional simulation tools are used extensively in the automotive industry to improve and optimize engine design for WOT performance. They are useful in target setting and in assessing the effects of certain design changes (e.g. intake manifold, valve timing, exhaust manifold, etc.). Generally the inputs to these models are “nominal” values or curves from a particular set of data and, therefore, do not take into account design or assembly variations. Often times, performance expectations are not met due to these “real world” effects and may result in significant re-design and testing efforts. The purpose of this paper is to assess the impact of typical model input variation on engine performance and to instill greater confidence in the use of these models in forecasting performance. The approach taken is to collect, analyze, and categorize actual build measurements from a 4.6L 4V Ford engine that are considered important inputs for a one-dimensional modeling.

The use of Swirl-Vanes or Inlet Guide Vanes (IGV) in gas engines is well-known and has demonstrated their ability to improve compressor surge margin at low flow rates. But, the use of swirl-vanes is not too common in large diesel engine turbo-chargers where compressor housing inlet has some form of Casing-Treatment (CT). Recently, Ford engineers tested swirl-vanes in a diesel engine turbocharger where the compressor inlet had a ported shroud casing-treatment and the experimental data showed no improvement in surge margin. Computational Fluid Dynamics (CFD) analyses were performed to investigate reasons why the surge margin did not improve after introducing swirl-vanes at the compressor inlet. The CFD results showed strong interactions between swirling flow at the compressor inlet and flow stream coming out of the compressor inlet casing-treatment.

The Single Sequential Turbocharger (SST) used in Ford’s 6.7L Scorpion Diesel is analyzed using Computational Fluid Dynamics (CFD) to draw conclusions about the compressor stability at low mass flows. The SST compressor concept consists of a double-sided wheel which flows in parallel fed by two separate inlets (front and rear), followed by a single vane-less diffuser, and a volute. CFD simulations for the full stage are performed at low mass flow rates Both, front and rear, sides have ported shroud casing-treatment (CT) in the inlet region. An objective of the analysis is to determine which side of the SST unit compressor (front or rear on the double-sided wheel) suffers flow break down first as the mass flow is reduced, and its impact on the overall stability of the SST compressor. Another objective is to better understand the interactions between the compressor inlet flow and the flow through the casing-treatment.

The conventional ported shroud recirculation casing treatment elevates narrowband noise at blade pass frequency. A new ported shroud recirculating casing treatment was implemented in Ford’s 3.5L turbo gas engine as Noise Vibration and Harshness (NVH) counter measure to reduce whoosh (broadband flow noise) noise without elevating narrowband noise at blade pass frequency. The new ported shroud design incorporates holes between the main and secondary recirculating passage and a slight cross-sectional area reduction just upstream of the impeller. These design features reduce whoosh noise without elevating the first order and the sixth order tonal noise at blade pass frequency. The new ported shroud design decreases narrowband tonal noise sound pressure level by 3-6 dB in the low to mid flow region compared to the baseline design. Computational Fluid Dynamics (CFD) tools were used to develop this casing treatment design.

The advent of turbochargers and the Eco-Boost technology at Ford in gasoline engines creates new challenges that need to be addressed with innovative designs. One of them is flow induced noise caused by airflow entering the turbocharger during off design operation. At certain vehicle operation conditions, the mass flow rate and pressure ratio are such that compressor wheel can generate a wide range of acoustic frequencies. Characterization of ‘whistles’ or pure tonal noises, ‘whoosh’ or broad band frequency noise caused by flow separation from the blade surfaces, and chirps, where the frequency increases or decreases with time are a few of the common error states. Understanding the fundamental mechanisms of such noise generation is necessary for developing effective countermeasures for the noise source generation. Computational Aero-Acoustic (CAA) analyses are performed to study the effects of inlet and outlet conditions to find the source of the noise.