Variable Valve Timing-A Possibility to Control Engine load without Throttle

Lenz, Hans Peter; Wichart, Klaus; Gruden, Dušan

doi:10.4271/880388

Cited by 47 publications

(7 citation statements)

References 2 publications

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“…Early IVC controls engine load by closing the inlet valve when sufficient charge has been admitted into the cylinder. Reductions in Brake Specific Fuel Consumption of up to 10% have been observed with early IVC strategies [29,30]. Recent studies by Fontana et al [31] and by Cairns et al [32] show similar reductions in fuel consumption, but explain these referring to the displacement of fresh air with combustion products during the valve overlap interval, which reduces the need for throttling.…”

Section: Vvt Strategies and Influence On Charge Diluent Fractionmentioning

confidence: 96%

Premixed Combustion in Spark Ignition Engines and the Influence of Operating Variables

Bonatesta¹

2013

Advances in Internal Combustion Engines and Fuel Technologies

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Advances in Internal Combustion Engines and Fuel Technologies 4 . . Overview of flame propagation mechanismDetailed observations of development and structure of the flame in SI engines can be made by using direct photographs or other methods such as Schlieren and shadowgraph photography techniques [ , ]. The initial stage of the combustion process is the development of a flame kernel, centred close to the spark-plug electrodes, that grows from the spark discharge with quasispherical, low-irregular surface its outer boundary corresponds to a thin sheet-like developing reaction front that separates burned and unburned gases. Engine combustion takes place in a turbulent environment produced by shear flows set up during the induction stroke and then modified during compression. Initially, the flame kernel is too small to incorporate most of the turbulence length scales available and, therefore, it is virtually not aware of the velocity fluctuations [ ]. Only the smallest scales of turbulence may influence the growing kernel, whereas bigger scales are presumed to only convect the flame-ball bodily the initial burning characteristics are similar to those found in a quiescent environment a laminar-like combustion development . As the kernel expands, it progressively experiences larger turbulent structures and the reaction front becomes increasingly wrinkled. During the main combustion stage, the thin reaction sheet becomes highly wrinkled and convoluted and the reaction zone, which separates burned and unburned gases, has been described as a thick turbulent flame brush. While the thickness of the initial sheet-like reaction front is of the order of . mm, the overall thickness of this turbulent flame brush can reach several millimetres this would depend on type of fuel, equivalence ratio and level of turbulence. The turbulent flow field, in particular velocity fluctuations, determines a conspicuous rate of entrainment in the reaction zone, which has been described [ , ] as being composed of many small pockets and isolated island of unburned gas within highly marked wrinkles that characterize a thin multi-connected reaction sheet. Theories have been advanced that describe the local boundary layer of this region as a quasi-spherical flame front, which diffuses outwards with laminar flame speed [ ].Gillespie and co-workers provide a useful review of those aspects of laminar and turbulent flame propagation, which are relevant to SI engines combustion [ ]. Similarly to laminar-like combustion taking place in a quiescent environment, two main definitions of time-based combustion rate can be proposed for turbulent combustion. The first one relates to the rate of formation of burned products velocity. The dependence of the combustion rate on turbulence is embodied in the velocity term, which is fundamentally modelled as a function of turbulence intensity, u ' , and laminar burning velocity, S L . The latter, loosely addressed to as laminar flame velocity in the context of simplified flame propagation models, has been demonstra...

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Section: Vvt Strategies and Influence On Charge Diluent Fractionmentioning

confidence: 96%

Premixed Combustion in Spark Ignition Engines and the Influence of Operating Variables

Bonatesta¹

2013

Advances in Internal Combustion Engines and Fuel Technologies

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“…Because of fresh mixture backflow at low engine speed, and inertia of the incoming gas flow at higher speed [11], the IVC timing shows significant effects on cylinder trapped mass, and hence on the resulting pumping (intake throttling) losses. Sizeable improvements in thermal efficiency have been observed with early IVC strategies, owing to greater effective compression ratio [12,13].…”

Section: Variable Camshaft Timingmentioning

confidence: 99%

Fuel economy analysis of part-load variable camshaft timing strategies in two modern small-capacity spark ignition engines

et al. 2016

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 Valve timing strategies are explored at part-load in two small-capacity SI engines  Simplified graphical fuel-economy VCT strategies are provided for the two engines  Engine design specifics exert a profound influence upon optimal valve timings  The theoretical best strategy determines BSFC reduction above 8% for the PFI engine  Maximum BSFC reduction was about 5% for the more efficient GDI platform ABSTRACT Variable Camshaft Timing strategies have been investigated at part-load operating conditions in two 3-cylinder, 1.0-litre, Spark Ignition engines. The two small-size engines are different variants of the same 4-valve/cylinder, pent-roof design platform. The first engine is naturally aspirated, port fuel injection and features high nominal compression ratio of 12:1. The second one is the turbo-charged, direct injection version, featuring lower compression ratio of 10:1. The aim of the investigation has been to identify optimal camshaft timing strategies which maximise engine thermal efficiency through improvements in brake specific fuel consumption at fixed engine load. The results of the investigation show that the two engines demonstrate consistent thermal efficiency response to valve timing changes in the low and mid part-load envelope, up to a load of 4 bar BMEP. At the lower engine loads investigated, reduced intake valve opening advance limits the hot burned gas internal recirculation, while increasingly retarded exhaust valve opening timing favours engine efficiency through greater effective expansion ratio. At mid load (4 bar BMEP), a degree of intake advance becomes beneficial, owing mostly to the associated intake de-throttling. In the upper partload domain, for engine load of 5 bar BMEP and above, the differences between the two engines determine very different efficiency response to the valve timing setting. The lower compression ratio engine continues to benefit from advanced intake valve timing, with a moderate degree of exhaust timing retard, which minimises the exhaust blow-down losses. The higher compression ratio engine is knock-limited, forcing the valve timing strategy towards regions of lower intake advance and lower hot gas recirculation. The theoretical best valve timing strategy determined peak fuel economy improvements in excess of 8% for the port fuel injection engine; the peak improvement was 5% for the more efficient direct injection engine platform.

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“…Numerous camshaft-based variable-valve mechanisms have been developed [1,.9, 10,11,14,18,26,27,29,30,33,38,47,54]. A recent search on U.S. patent data base with the phrase 'variable valve timing" resulted in 196 patents.…”

Section: Background and Technical Objectivesmentioning

confidence: 99%

Electrohydraulic Valve-trains for Direct Injection Compression Ignition Camless Engine Operations - Phase I Project Final Report

Tsao¹,

Tai²,

Stubbs³

et al. 2000

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Variable Valve Timing-A Possibility to Control Engine load without Throttle

Cited by 47 publications

References 2 publications

Premixed Combustion in Spark Ignition Engines and the Influence of Operating Variables

Premixed Combustion in Spark Ignition Engines and the Influence of Operating Variables

Fuel economy analysis of part-load variable camshaft timing strategies in two modern small-capacity spark ignition engines

Electrohydraulic Valve-trains for Direct Injection Compression Ignition Camless Engine Operations - Phase I Project Final Report

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