Variable Valve Actuation Mechanisms and the Potential for their Application

Stone, Richard; Kwan, Eric

doi:10.4271/890673

Cited by 41 publications

(5 citation statements)

References 39 publications

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“…As a result, it is difficult to obtain the necessary change in the closing of intake valve; late closing is more appropriate in cases where the change in timing is minor [13]. Difficulties in variable valve timing, the fact that the resulting increase in efficiency is higher than the energy needed to drive the developed system, the low number of parts used, the long service life of the system, its failure-proof quality, and other factors have cause several methods to be researched for system development, although very few of them have become commercialized.…”

Section: • the Obtained Values Indicate That Depending On The Enginementioning

confidence: 99%

The Effects of a Pneumatic-Driven Variable Valve Timing Mechanism on the Performance of an Otto Engine

Uysal

Sağiroğlu

2015

SV-JME

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In this study, the classic cam mechanism of a single cylinder, four-stroke, 6 hp spark-ignited engine was replaced by an electro-pneumatic rocker mechanism, which is designed and manufactured to open the intake valve at low (3.7 mm), normal (5.7 mm) and high (7.7 mm) lifts between engine speeds of 1600 rpm to 2200 rpm. An air compressor was used to feed 6 bar air pressure in order to have the plungers drive the cams in an orderly manner. A control panel was used to control plungers in order to modulate the valve lifts gradually. The volumetric efficiency, torque, power and specific fuel consumption with this operation were measured at full load and compared to the values with a classic cam mechanism. The results of the study showed that decreasing the valve lift at low engine speeds and increasing the lift at high speeds improve the engine performance. Moreover, it was concluded that the idle speed can be lowered by decreasing the valve lift at low engine speeds.

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Section: • the Obtained Values Indicate That Depending On The Enginementioning

confidence: 99%

The Effects of a Pneumatic-Driven Variable Valve Timing Mechanism on the Performance of an Otto Engine

Uysal

Sağiroğlu

2015

SV-JME

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“…The high compression ratio required for starting is often higher than required for best economy as the thermodynamic gains of high compression ratio are outweighed by the consequent reduction in mechanical efficiency [4]. The use of VVT to increase the effective compression ratio allows the nominal compression ratio of the engine to be reduced, which not only maintains or improves cold starting, but also has implications to output:…”

Section: The Effects Of Valve Timing On Effective Compression Ratiomentioning

confidence: 99%

“…However, since VVT can allow an engine to operate with a lower nominal compression ratio, the BMEP can theoretically be increased, (by increasing the boost levels) within the same maximum cylinder pressure limitations. It has been suggested that raising and flattening the torque curve, of a diesel engine, should be possible with variable valve actuation [34] [4]. This would result in increased power as well as improving the shape of the torque curve.…”

Section: The Effects Of Valve Timing On Effective Compression Ratiomentioning

confidence: 99%

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The Application of Variable Event Valve Timing to a Modern Diesel Engine

Lancefield¹,

Methley²,

Räse³

et al. 2000

SAE Technical Paper Series

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DaimlerChrysler and Mechadyne have undertaken a piece of work to investigate the opportunities for improving the operation of light duty diesel engines using variable valve timing. The very high compression ratios used in this type of engine make it essential to be able to alter the valve open periods to affect exhaust valve opening and intake valve closing, whilst leaving the valve motions largely unchanged around overlap top dead centre to avoid valve to piston contact. This paper presents an overview of the design solution, a description of the simulation model used, performance and economy data predicted by the model and a discussion of other areas of opportunity where improvements may be possible.

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“…Valve event variation is one of the research fields more exploited in engine technology. Several variable valve actuating systems have been proposed [3][4][5] and results reported. The variation of the intake valve closure timing on itself can produce variations of the amount of air/fuel mixture trapped within the cylinder in each engine cycle.…”

Section: Introductionmentioning

confidence: 99%

Direct Comparison of an Engine Working under Otto, Miller and Diesel Cycles: Thermodynamic Analysis and Real Engine Performance

Ribeiro

Martins

2007

SAE Technical Paper Series

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One of the ways to improve thermodynamic efficiency of Spark Ignition engines is by the optimisation of valve timing and lift and compression ratio. The throttleless engine and the Miller cycle engine are proven concepts for efficiency improvements of such engines. This paper reports on an engine with variable valve timing (VVT) and variable compression ratio (VCR) in order to fulfill such an enhancement of efficiency. Engine load is controlled by the valve opening period (enabling throttleless operation and Miller cycle), while the variable compression ratio keeps the efficiency high throughout all speed and load conditions. A computer model is used to simulate such an engine and evaluate its improvement potential, while a single cylinder engine demonstrates these results. The same base engine was run on the test bench under the Diesel cycle, Otto cycle and Miller cycle conditions, enabling direct thermodynamic comparisons under a wide variety of conditions of speed and load. The results show a significant improvement of the Miller cycle over the Otto cycle engine. Comparisons of the Miller engine with the Diesel engine shown that it is possible to have a SI engine with better efficiency than a similar Diesel engine for most of the working conditions.

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Variable Valve Actuation Mechanisms and the Potential for their Application

Cited by 41 publications

References 39 publications

The Effects of a Pneumatic-Driven Variable Valve Timing Mechanism on the Performance of an Otto Engine

The Effects of a Pneumatic-Driven Variable Valve Timing Mechanism on the Performance of an Otto Engine

The Application of Variable Event Valve Timing to a Modern Diesel Engine

Direct Comparison of an Engine Working under Otto, Miller and Diesel Cycles: Thermodynamic Analysis and Real Engine Performance

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