Development Experience of a Poppet-Valved Two-Stroke Flagship Engine

Stokes, John; Hundleby, G.E.; Lake, T. H.; Christie, Mark

doi:10.4271/920778

Cited by 34 publications

(15 citation statements)

References 3 publications

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“…The elimination of the overhead valvetrain is largely responsible for both of these advantages; yet some researchers are still applying overhead valves in their two-stroke engines to overcome the durability and exhaust oil contamination issues. (12)(13)(14)(15) The availability of specific engine data for automotive class two-stroke engines is poor because of the highly competitive environment; current developers are not anxious to release their data.…”

Section: Two-stroke Spark-ignited Enginesmentioning

confidence: 99%

A Survey of Technology for Hybrid Vehicle Auxiliary Power Units.

Widener¹

1995

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Section: Two-stroke Spark-ignited Enginesmentioning

confidence: 99%

A Survey of Technology for Hybrid Vehicle Auxiliary Power Units.

Widener¹

1995

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“…By means of direct fuel injection and an optimised combustion system, it is possible to realise two-stroke cycle operation in the poppet-valved engine without the shortcomings of the conventional ported two-stroke engines. 5,6 Furthermore, with the development and availability of variable valve timing (VVT) and high-efficiency boosting devices as well as more flexible fuel injection equipment (FIE), a poppet-valved two-stroke engine can be boosted to produce superior low-speed torque than the turbocharged four-stroke engine as demonstrated in a previous study. 7 However, to avoid the unstable SI combustion and hence poor fuel economy at part load of the two-stroke cycle operation, four-stroke SI combustion was retained and a sophisticated two- or four-stroke switching system and control had to be included in the engine.…”

Section: Introductionmentioning

confidence: 99%

Optimisation of boosting strategy for controlled auto-ignition combustion in a four-valve camless gasoline direct injection engine running in two-stroke cycle

Zhang

Zhao

2014

International Journal of Engine Research

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Due to their ability to simultaneously reduce fuel consumption and NOx emissions, controlled autoignition or homogeneous charge compression ignition combustion processes have been extensively researched over the last decade and adopted on prototype gasoline engines. Despite the fact that they were initially achieved on conventional two-stroke ported gasoline engines, there have been much fewer studies carried out on controlled autoignition combustion in two-stroke engines because of the inherent problems associated with the conventional two-stroke engine with intake and exhaust ports. In the meantime, engine downsizing has been actively researched and developed as an effective means to improve the vehicle’s fuel economy by operating the engine at higher load and more efficient regions and by reducing the number of cylinders. But the aggressive engine downsizing of the current four-stroke gasoline engine is limited by the knocking combustion and high peak cylinder pressure. As an alternative approach to engine downsizing, the boosted two-stroke cycle in a poppet valve engine is proposed and researched. It has been shown that the controlled autoignition combustion in the two-stroke cycle could be readily achieved and it led to significant reduction in carbon monoxide and unburned hydrocarbon emissions than the spark ignition combustion. In this study, extensive engine experiments have been performed to determine the optimum boosting for minimum fuel consumption in a single-cylinder gasoline direct injection camless engine operating in the two-stroke cycle. In order to minimise the air short-circuiting rate, the intake and exhaust valve timings were adjusted. Lean boost was applied to the engine operation, which was found to extend the range of controlled autoignition combustion, result in higher combustion and thermal efficiencies and significantly lower carbon monoxide and hydrocarbon emissions. By means of the cycle-resolved in-cylinder measurements and heat release analysis, the improvement in combustion and thermal efficiencies was attributed to the improved in-cylinder mixture, optimised autoignition and combustion phases.

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“…In order to reduce the short-circuiting phenomenon of charge and enable the intake boosting, the poppetvalved two-stroke engines, which have the same intake and exhaust valve designs in the cylinder head as the four-stroke engines, were proposed in the 1990s. [1][2][3][4][5][6] As shown in Figure 1, the two-stroke operation is achieved by means of the gas scavenging process during the valve overlap period around the bottom dead center (BDC) at every engine revolution.…”

Section: Introductionmentioning

confidence: 99%

“…By adopting top-entry intake ports in combination with a stepped surface around the intake valves, the scavenging efficiency was significantly improved at a given boost pressure and engine speed. [1][2][3] Although it has been proved that the reversed tumble flow in poppet-valved two-stroke engines is useful in reducing short-circuiting, there has been little discussion by far, on how this type of flow, subjected to the intake ports and combustion chamber designs, influences the scavenging performance which is of paramount importance to adjust the amount of residuals and fresh air trapped in the cylinder and hence the engine load control. In addition, the reversed tumblecontrolled scavenging process also affects the temporal and spatial distribution of the residual gas and air in the cylinder.…”

Section: Introductionmentioning

confidence: 99%

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Influences of intake ports and pent-roof structures on the flow characteristics of a poppet-valved two-stroke gasoline engine

Zhao

2016

International Journal of Engine Research

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In order to minimize the short-circuiting of the intake charge in a poppet-valved two-stroke engine, a ''step structure'' on the intake side of the pent-roof was employed to shroud the bulk flow at the upper periphery of the intake valves at low valve lifts. Several intake-port geometries and pent-roof angles were evaluated on their charging and reversed tumble generating abilities using a steady flow test rig built in computational fluid dynamics, among which top-entry ports and relatively small pent-roof angle were selected. The scavenging processes of the two-stroke engine at high load and 3000 r/min condition with different intake valve seat heights were simulated and evaluated. The local flow patterns and composition distribution were also studied. The results show that lowering the intake valve seat height achieves higher delivery ratio and charging efficiency, but marginally better scavenging efficiency and slightly lower trapping efficiency. The scavenging process experiences a slow displacement period due to low flow momentum for the high valve seat cases and flow interaction at the exhaust exits for the low valve seat cases. Reversed tumble is the dominant flow pattern during the scavenging process. The lower the valve seat, the higher the tumble ratio in the early stage and at the end of the scavenging period. For all valve seat configurations, the least scavenged regions are located near the engine head wall and between the intake and the exhaust valves, while the regions rich in fresh charge are located along the major path of the reversed tumble. Low intake valve seat height is effective in increasing the overall in-cylinder air proportion. Further reducing it can result in higher fresh charge proportion below the exhaust valves and near the head wall.

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Development Experience of a Poppet-Valved Two-Stroke Flagship Engine

Cited by 34 publications

References 3 publications

A Survey of Technology for Hybrid Vehicle Auxiliary Power Units.

A Survey of Technology for Hybrid Vehicle Auxiliary Power Units.

Optimisation of boosting strategy for controlled auto-ignition combustion in a four-valve camless gasoline direct injection engine running in two-stroke cycle

Influences of intake ports and pent-roof structures on the flow characteristics of a poppet-valved two-stroke gasoline engine

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