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Separation in double entry turbine housings in boosted gasoline engines

'Separation in double entry turbine housings in boosted gasoline engines'
SYSTEM ADVANTAGES Turbocharging in combination with direct injection and variable valve tim- ing represents the major technology trend in modern gasoline engine con- cepts for achieving high specifi c power output with low fuel consumption at the same time. In this context the separation of cylinder blow down events is benefi - cial for the trade-off between high spe- cifi c power output on the one hand and compelling low-end torque performance on the other hand. Cylinder blow down separation can be accomplished through different technological strategies, e.g. scroll separation in turbine or variable exhaust valve event, ?. The advantages are seen during the gas exchange (e.g. high engine pressure difference) as well as in the reduced in-cylinder residual gas and hence reduced knock sensitivity. Additionally longer exhaust valve events are possible resulting in reduced part load fuel consumption. A Bi-turbo concept can completely avoid the unwanted interaction between the exhaust branches. According to [1] the advantages of double entry housings out- weigh single entry even in the case of a non-ideal separation. Along with im - proved turbine power output (due to pulse charging) the concept leads to higher AUTHORS DIPL.-ING. DOMINIK LÜCKMANN is Scientific Assistant at the Institute for Combustion Engines of RWTH Aachen University (germany). DIPL.-ING. TOLGA UHLMANN is Team Manager Air and Exhaust Management in the Business Unit gasoline Engines of FEV gmbH in Aachen (germany). DR.-ING. HELMUT KINDL is Technical Specialist Engine Boosting Systems powertrain R the inner scroll close to the bearing housing features a higher mass flow due to a more favourable flow towards the turbine wheel. Single admission is characterised by one scroll being blocked. Hence, the flow into the turbine wheel takes place 10I2013 Volume 745 only through one scroll and the mass flow ratio takes on values of MFR = 1 or MFR = 0 respectively. The flow conditions present at equal and single admission can be considered as a special form between engine cycle dominant unequal admission and cross flow. During different unequal admissions the mass flow rate will vary between MFR = 0 and MFR = 1 whilst during the blow-down phase due to high pres- sure differences between the two scrolls, cross flow can occur. This means that at the same time a fraction of the mass flow going through the scroll with higher pressure level does not reach the turbine wheel, but recirculates into the second scroll in front of the wheel. Coinciden- tally the mass flow ratio is less than zero or larger than one when cross flow occurs. The predominant flow condition has a great influence on the reduced mass flow rate and the turbine wheel efficiency. ? illustrates that modelling only on the basis of equal admission (green), as it is still widely used today, incompletely reflects the behaviour of double entry housings. On one hand the characteristics of the efficiency as a function of the pres- sure rati
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Separationindoubleentryturbinehousingsinboostedgasolineengines
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