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Research Papers: Gas Turbines: Combustion, Fuels, and Emissions

A Comparison of Valving Strategies Appropriate for Multimode Combustion Within a Downsized Boosted Automotive Engine—Part II: Mid Load Operation Within the SACI Combustion Regime

[+] Author and Article Information
Matthew S. Gerow

Walter E. Lay Automotive Laboratory,
University of Michigan,
1231 Beal Avenue,
Ann Arbor, MI 48109
e-mail: matthewsgerow@gmail.com

Prasad S. Shingne

Walter E. Lay Automotive Laboratory,
University of Michigan,
1231 Beal Avenue,
Ann Arbor, MI 48109
e-mail: sunand@umich.edu

Vassilis Triantopoulos

Walter E. Lay Automotive Laboratory,
University of Michigan,
1231 Beal Avenue,
Ann Arbor, MI 48109
e-mail: vtrianto@umich.edu

Stanislav V. Bohac

Walter E. Lay Automotive Laboratory,
University of Michigan,
1231 Beal Avenue,
Ann Arbor, MI 48109
e-mail: sbohac@umich.edu

Jason B. Martz

Walter E. Lay Automotive Laboratory,
University of Michigan,
1231 Beal Avenue,
Ann Arbor, MI 48109
e-mail: jmartz@umich.edu

1Corresponding author.

Contributed by the Combustion and Fuels Committee of ASME for publication in the JOURNAL OF ENGINEERING FOR GAS TURBINES AND POWER. Manuscript received February 16, 2014; final manuscript received March 28, 2014; published online May 2, 2014. Editor: David Wisler.

J. Eng. Gas Turbines Power 136(10), 101508 (May 02, 2014) (11 pages) Paper No: GTP-14-1097; doi: 10.1115/1.4027360 History: Received February 16, 2014; Revised March 28, 2014

Spark assisted compression ignition (SACI) is a combustion mode that may offer significant efficiency improvements compared to conventional spark-ignited combustion systems. Unfortunately, SACI is constrained to a relatively narrow range of dilution levels and top dead center temperatures. Both positive valve overlap (PVO) and negative valve overlap (NVO) strategies may be utilized to attain these conditions at low and intermediate engine loads. The current work compares 1D thermodynamic simulations of PVO valving strategies and a baseline NVO strategy in a downsized boosted automotive engine with variable valve timing capability. As future downsized boosted engines may employ multiple combustion modes, the goal of this work is the definition of valving strategies appropriate for SACI combustion at low to moderate loads and spark ignition (SI) combustion at moderate to high loads for an engine with fixed camshaft profiles. PVO durations, valve opening timings, and peak lifts are investigated at low to moderate loads and are compared to a baseline NVO configuration in order to assess valving strategies appropriate for multimode combustion operation. A valvetrain kinematic model is used to translate the desired valve lift profiles into camshaft profiles while a kinematic analysis is used to calculate piston to valve clearances and to define the practical limits of the PVO strategies. The NVO and PVO strategies are also compared to throttled SI operation at part load to assess the overall efficiency benefit of operating under the thermodynamic conditions of the SACI combustion regime. While the results of this study are engine specific, there are several camshaft profiles that are appropriate for the use of PVO rebreathing type valve events. For the range of PVO valve events examined and taking into consideration piston to valve interference, the use of high exhaust and low intake lifts with early exhaust valve opening timing and long PVO durations enables high levels of internal exhaust gas recirculation (EGR) with relatively low pumping losses.

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References

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Figures

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Fig. 1

Internal EGR as function of PVO for various valve timings and lifts

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Fig. 2

Total residual as a function of PVO for various valve timings and lifts

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Fig. 3

Internal EGR for varying EVO and PVO with high lift exhaust and low lift intake valves

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Fig. 4

Valve lifts and mass flow rates comparing cases A and B

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Fig. 5

Valve lifts and mass flow rates comparing cases C and D

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Fig. 6

External EGR for varying EVO and PVO with high lift exhaust and low lift intake valves

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Fig. 7

Total residual for varying EVO and PVO with high lift exhaust and low lift intake valves

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Fig. 8

Fuel to charge equivalence ratio for varying EVO and PVO with high lift exhaust and low lift intake valves

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Fig. 9

Unburned gas temperature at TDC for varying EVO and PVO with high lift exhaust and low lift intake valves

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Fig. 10

Calculated auto-ignition crank angle for varying EVO and PVO with high lift exhaust and low lift intake valves

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Fig. 11

Brake mean effective pressure for varying EVO and PVO with high lift exhaust and low lift intake valves

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Fig. 12

Pumping mean effective pressure for varying EVO and PVO with high lift exhaust and low lift intake valves

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Fig. 13

Pressure-volume trace comparison of pumping loops comparing early and late exhaust valve opening at 63 deg PVO with high lift exhaust and low lift intake valves

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Fig. 14

Pressure-volume trace comparison of pumping loops comparing high and low PVO with EVO at 45 deg bBDC with high lift exhaust and low lift intake valves

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Fig. 15

Gross indicated thermal efficiency for varying EVO and PVO with high lift exhaust and low lift intake valves

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Fig. 16

Net indicated and brake thermal efficiency for varying EVO and PVO with high lift exhaust and low lift intake valves

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Fig. 17

Variations of valve overlap and EVO timings for the PVO and NVO comparison against load

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Fig. 18

Combustion mode comparison of total residual and internal residual against load

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Fig. 19

Combustion mode comparison of fuel to charge equivalence ratio against load

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Fig. 20

Combustion mode comparison of TDC unburned gas temperature against load

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Fig. 21

Effect of total residual on TDC unburned gas temperature

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Fig. 22

Combustion mode comparison of gross indicated thermal efficiency against load

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Fig. 23

Combustion mode comparison of pumping losses against load

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Fig. 24

Pumping loop comparison between PVO and NVO at ∼5.5–6.0 bar BMEP

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Fig. 25

Combustion mode comparison of net indicated and brake thermal efficiency against load

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