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Evaluation of Variable Camshaft Effects on Performance of a High Output, 4-Valve SI Engine
Technical Paper
905173
Sector:
Language:
English
Abstract
An analytical and experimental evaluation was carried out to
determine the effects of variable intake and exhaust cam timing on
the performance of a high output, 4-valve SI engine. The engine is
free- breathing and has highly tuned intake and exhaust manifolds.
The analysis was carried out using an engine analysis code which
has the capability to calculate the processes occurring within each
individual engine cylinder, and, through gas dynamic analysis, also
the flow and pressure dynamics within the intake and exhaust
manifolds. The latter capability is essential in simulations of
engines which have significant tuning effects which result from the
design of their manifolds.
The analytical part of the study first addressed the effects of
timing variations of stock intake and exhaust camshafts at wide
open throttle. Then a broader study was carried out to determine
the effects of variable valve timing coupled with variation of
valve-open duration. Brake torque increases of up to 11.5% were
observed. At road load operating points, variable timing was found
to enable control of exhaust residuals resulting in a favorable
impact on fuel economy and NOx generation. At idle, variable
timing was found to reduce trapped residuals through a reduction in
valve overlap. Non- tuned manifolds were found to produce results
similar in magnitude to those seen with the baseline highly tuned
manifolds. Experimental data were acquired to address some of the
key conclusions of the analytical study, and a good agreement was
found between the analysis and the experiment.