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Numerical investigation of turbolag reduction in HD CNG engines by means of exhaust valve variable actuation and spark timing control

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Abstract

Turbocharging port-injected Natural Gas (NG) engines allows them to recover gaseous-fuel related power gap with respect to gasoline engines. However, turbolag reduction is necessary to achieve high performance during engine transient operations and to improve vehicle fun-to-drive characteristics. Significant support for the study of turbocharged Compressed Natural Gas (CNG) engines and guidelines for the turbo-matching process can be provided by 1-D numerical simulation tools. However, 1-D models are predictive only when a careful tuning procedure is set-up and carried out on the basis of the experimental data. In this paper, a 1-D model of a Heavy-Duty (HD) turbocharged CNG engine was set up in the GT-POWER (Gamma Technologies Inc., Westmont, IL, US) environment to simulate transient operations and to evaluate the turbolag. An extensive experimental activity was carried out to provide experimental data for model tuning. The model buildup and tuning processes are described in detail with specific reference to the turbocharger model, whose correct calibration is a key factor in accounting for the effects of turbine flow pulsations. The second part of the paper focuses on the evaluation of different strategies for turbolag reduction, namely, exhaust valve variable actuation and spark timing control. Such strategies were aimed at increasing the engine exhaust-gas power transferred to the turbine, thus reducing the time required to accelerate the turbocharger group. The effects of these strategies were examined for tip-in maneuvers at a fixed engine speed. Depending on the engine speed and the applied turbolag reduction strategy, turbolag reductions from 70% to 10% were achieved.

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Abbreviations

A:

advance of EVO

bmep:

brake mean effective pressure

BSR:

blade speed ratio

cp :

air specific heat at constant pressure

C:

engine brake torque

CA:

crank angle

CNG:

compressed natural gas

Cs :

isentropic gas velocity

E:

Wiebe exponent

E-EVO:

early exhaust valve opening

EVO:

exhaust valve opening

HRR:

heat release rate

IC:

inter-cooler

L:

lift (of the exhaust valve)

ṁ:

mass flow rate

MAP:

manifold absolute pressure

N:

engine speed

n:

turbocharger shaft speed

NG:

natural gas

p:

in-cylinder pressure at EVO

P:

prelift (of the exhaust valve)

PFP:

peak firing pressure

PR:

pressure ratio/turbine pressure ratio

SOC:

start of combustion

ST:

spark timing

t:

time

T:

temperature

U:

rotor blade tip speed

UEGO:

universal exhaust gas oxygen

VVA:

variable valve actuation

WC:

Wiebe constant

WG:

waste gate

WOT:

wide open throttle

xb :

burned mass fraction

γ :

ratio of specific heats (of air)

η :

efficiency

θ :

crank angle

τ :

duration of the transient

O:

total conditions

′:

burned gas

—:

time-averaged value

air:

air

c:

combustion

cmp:

compressor

exh:

exhaust gases

in:

inlet

max:

maximum value

red:

reduced

trb:

turbine

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Authors and Affiliations

  1. IC Engines Advanced Laboratory, Politecnico di Torino, Torino, 10129, Italy

    M. Baratta & E. Spessa

  2. Centro Ricerche Fiat, Orbassano, 10043, Italy

    P. Mairone

Authors
  1. M. Baratta
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  2. E. Spessa
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  3. P. Mairone
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Correspondence to E. Spessa.

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Baratta, M., Spessa, E. & Mairone, P. Numerical investigation of turbolag reduction in HD CNG engines by means of exhaust valve variable actuation and spark timing control. Int.J Automot. Technol. 11, 289–306 (2010). https://doi.org/10.1007/s12239-010-0037-x

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  • DOI: https://doi.org/10.1007/s12239-010-0037-x

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