An investigation and evaluation of variable-valve-timing and variable-valve-actuation strategies in a diesel homogeneous charge compression ignition engine using three-dimensional computational fluid dynamics

Homogeneous charge compression ignition (HCCI) is a promising low-temperature combustion strategy for reducing NOx emissions and increasing efficiency in internal combustion engines. However, HCCI has no direct combustion initiator and, when achieved by reinducting or trapping residual exhaust gas with a variable valve actuation (VVA) system, becomes a dynamic process as the temperature of the residual gas couples one cycle to the next. These characteristics of residual-affected HCCI present a challenge for control engineers and a barrier to implementing HCCI in a production engine. In order to address these challenges, this paper outlines physics-based control strategies for both the VVA system and the HCCI combustion process. The results show that VVA system control can provide arbitrary valve timings on a cycle-to-cycle basis, enabling tight control of HCCI. By abstracting these valve timings further into an inducted gas composition and an effective compression ratio, model-based controllers can be developed to control simultaneously load and combustion timing in an HCCI engine.

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Computational fluid dynamics simulation of in-cylinder flows in a motored homogeneous charge compression ignition engine cylinder with variable negative valve overlapping

Proceedings of the Institution of Mechanical Engineers Part D Journal of Automobile Engineering ◽

10.1243/09544070jauto355 ◽

2007 ◽

Vol 221 (10) ◽

pp. 1295-1304 ◽

Cited By ~ 6

Author(s):

A-F M Mahrous ◽

M L Wyszynski ◽

T Wilson ◽

H-M Xu

Keyword(s):

Fluid Dynamics ◽

Computational Fluid Dynamics ◽

Homogeneous Charge Compression Ignition ◽

Compression Ignition ◽

Hcci Engine ◽

Mixture Preparation ◽

Engine Cylinder ◽

The Times ◽

Exhaust Valves ◽

Predictive Study

In-cylinder air motion is one of the most important factors that control the degree of mixture preparation and thus is fundamental to improvements in the combustion process and overall engine performance. The major aim of this paper is to elucidate, through a predictive study, the main features of in-cylinder flow fields in a motored homogeneous charge compression ignition (HCCI) engine cylinder with variable negative valve overlapping (NVO). A commercial finite-volume computational fluid dynamics (CFD) package was used in the programme of simulation. The computational model was validated through a qualitative comparison between CFD results and the available experimental data. Thus one of the main developments presented in this study is the investigation of the intake process of the HCCI engine with various valve strategies, and it is perhaps the first time (to the current authors' best knowledge) that a direct comparison has been made of the results obtained in the same HCCI NVO motored engine using modelling and experimental approaches. The comparison illustrated a fair agreement between both sets of results, with some differences. A parametric predictive study of the effects of variable valve timings on the in-cylinder air motion has then been carried out. Three different sets of valve timings have been applied to the intake and exhaust valves to generate NVO of 70, 90, and 110 degrees of crank angle (°CA). The NVO was controlled by adjusting the times of exhaust valves closing (EVC) and intake valves opening (IVO) while keeping the times of exhaust valves opening (EVO) and intake valves closing (IVC) unchanged. The predicted results show a noticeable modification of the strength and the global direction of the in-cylinder charge motion as a result of increasing the magnitude of NVO. Modifications of in-cylinder swirl and tumble motions obtained by applying higher degrees of NVO are expected to have a considerable effect on the air-fuel mixture preparation process as well as the actual in-cylinder conditions at the end of the compression stroke.

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Computational Fluid Dynamics Simulation of an Opposed-Piston Two-Stroke Gasoline Compression Ignition Engine

Volume 2: Emissions Control Systems; Instrumentation, Controls, and Hybrids; Numerical Simulation; Engine Design and Mechanical Development ◽

10.1115/icef2018-9713 ◽

2018 ◽

Cited By ~ 1

Author(s):

Ahmed Abdul Moiz ◽

Janardhan Kodavasal ◽

Sibendu Som ◽

Reed Hanson ◽

Fabien Redon ◽

...

Keyword(s):

Fluid Dynamics ◽

Computational Fluid Dynamics ◽

Dynamics Simulation ◽

System Level ◽

Experimental Program ◽

Compression Ignition ◽

Compression Ignition Engine ◽

Cfd Simulations ◽

System Level Simulation ◽

Light Duty

The paper describes the results from a computational fluid dynamics (CFD) simulation campaign that is complementary to an ongoing experimental program to develop an opposed-piston (OP) two-stroke gasoline compression ignition (GCI) engine for application in light-duty trucks. The simulation workflow and results are explained. First, open-cycle 3-D CFD simulations (in Converge CFD) are performed to simulate the scavenging process—gas exchange through the intake ports, cylinder, and exhaust ports. The results from these scavenging calculations are then fed into a model of this engine built in the system-level simulation tool (in GT-POWER), which in turn provides initial conditions for closed-cycle 3-D CFD simulations. These simulations are used to assess combustion by employing standard spray models and a chemical kinetic mechanism for gasoline. Validation of a representative set of engine operating points is performed in this way to gain confidence in the CFD model setup. Six injectors were then screened according to metrics of wall-wetting, maximum pressure rise rate, combustion efficiency and emission levels. Further CFD simulations have been carried out with parameter sweeps applying design of experiments (DoE) methods to finalize on candidate injectors, piston-bowls and injection strategies. The intended outcome of this program is a three-cylinder OP GCI engine equipped with a turbocharger and a supercharger targeting a 30% improvement in brake thermal efficiency (BTE) over conventional light-duty diesel engines.

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