scholarly journals CFD Analysis of a Large Marine Engine Scavenging Process

Processes ◽  
2022 ◽  
Vol 10 (1) ◽  
pp. 141
Author(s):  
Tomislav Senčić ◽  
Vedran Mrzljak ◽  
Vedran Medica-Viola ◽  
Igor Wolf

The scavenging process is an important part of the two-stroke engine operation. Its efficiency affects the global engine performance such as power, fuel consumption, and pollutant emissions. Slow speed marine diesel engines are uniflow scavenged, which implies inlet scavenging ports on the bottom of the liner and an exhaust valve on the top of the cylinder. A CFD model of such an engine process was developed with the OpenFOAM software tools. A 12-degree sector of the mesh was used corresponding to one of the 30 scavenging ports. A mesh sensitivity test was performed, and the cylinder pressure was compared to experimental data for the analyzed part of the process. The scavenging performances were analyzed for real operation parameters. The influence of the scavenge air pressure and inlet ports geometric orientation was analyzed. The scavenging process is analyzed by means of a passive scalar representing fresh air in the cylinder. Isosurfaces that show the concentration of fresh air were presented. The variation of oxygen and carbon dioxide with time and the axial and angular momentum in the cylinder were calculated. Finally, the scavenging performance for the various operation parameters was evaluated by means of scavenging efficiency, charging efficiency, trapping efficiency, and delivery ratio. It was found that the scavenging efficiency decreases with the engine load due to the shorter time for the process. The scavenging efficiency increases with the pressure difference between the exhaust and scavenging port, and the scavenging efficiency decreases with the increase in the angle of the scavenging ports. It was concluded that smaller angles than the industry standard of 20° could be beneficial to the scavenging efficiency. In the investigation, the charging efficiency ranged from 0.91 to over 0.99, the trapping efficiency ranged from 0.54 to 0.83, the charging efficiency ranged from 0.78 to 0.92, and the delivery ratio ranged from 1.21 to 2.03.

2020 ◽  
pp. 146808742091608 ◽  
Author(s):  
Zheng Xu ◽  
Fenzhu Ji ◽  
Shuiting Ding ◽  
Yunhai Zhao ◽  
Yan Wang ◽  
...  

Scavenging is becoming one of the determinants of two-stroke engine performance. Efficiency of U-type loop scavenging of two-stroke diesel engine with two poppet valves is generally unsatisfactory due to scavenging short-circuiting and large amount of residual burned gas in cylinder, and it is hard to generate the swirl that facilitates fuel spray mixing and combustion. In order to deal with the above issues, a swirl-loop scavenging configuration is proposed to involve swirl and depress short-circuiting. To investigate swirl-loop scavenging performance, this article simulates the scavenging process by numerical method, optimizes the tracer gas method to measure and evaluate the scavenging performance, as well as analyzes the influence factors. The results demonstrate that, compared with U-type loop scavenging, the trapping efficiency and scavenging efficiency of swirl-loop scavenging respectively increase by 8% and 10%. Change of engine speed has an impact on the delivery ratio and trapping efficiency but load does not. Both intake and exhaust valve timings affect scavenging performance and short-circuiting to a large extent. In addition, the accuracy of tracer gas method in measurement of scavenging performance parameters is improved, and the scavenging efficiency deviation between simulation and experiment is decreased from 6% to 2%.


Energies ◽  
2018 ◽  
Vol 11 (10) ◽  
pp. 2739 ◽  
Author(s):  
Yuan Qiao ◽  
Xucheng Duan ◽  
Kaisheng Huang ◽  
Yizhou Song ◽  
Jianan Qian

The two-stroke engine is a common power source for small and medium-sized unmanned aerial vehicles (UAV), which has wide civil and military applications. To improve the engine performance, we chose a prototype two-stroke small areoengine, and optimized the geometric parameters of the scavenging ports by performing one-dimensional (1D) and three-dimensional (3D) computational fluid dynamics (CFD) coupling simulations. The prototype engine is tested on a dynamometer to measure in-cylinder pressure curves, as a reference for subsequent simulations. A GT Power simulation model is established and validated against experimental data to provide initial conditions and boundary conditions for the subsequent AVL FIRE simulations. Four parameters are considered as optimal design factors in this research: Tilt angle of the central scavenging port, tilt angle of lateral scavenging ports, slip angle of lateral scavenging ports, and width ratio of the central scavenging port. An evaluation objective function based on the Benson/Bradham model is selected as the optimization goal. Two different operating conditions, including the take-off and cruise of the UAV are considered. The results include: (1) Orthogonal experiments are analyzed, and the significance of parameters are discussed; (2) the best factors combination is concluded, followed by simulation verification; (3) results before and after optimization are compared in details, including specific scavenging indexes (delivery ratio, trapping efficiency, scavenging efficiency, etc.), conventional performance indicators, and the sectional views of gas composition distribution inside the cylinder.


2017 ◽  
Vol 1 ◽  
pp. S5WGLD ◽  
Author(s):  
Wajid A. Chishty ◽  
Tak Chan ◽  
Pervez Canteenwalla ◽  
Craig R. Davison ◽  
Jennifer Chalmers

Abstract Alternative fuel for aviation has been the centre of serious focus for the last decade, owing mostly to the challenges posed by the price of conventional petroleum fuel, energy security and environmental concerns. The downslide in the oil prices in the recent months and the fact that energy security is not considered a major threat in commercial aviation, these factors have worked negatively for the promotion of alternative fuels. However, the continuous commitment to environmental stewardship by Governments and the industry have kept the momentum going towards the transparent integration of renewable alternatives in the aviation market. On the regulatory side, much progress have been made in the same timeframe with five alternative fuels being certified as synthetic blending components for aviation turbine fuels for use in civil aircraft and engines. Another seven alternative fuels are in the various stages of certification protocol. This progress has been made possible because of the extensive performance testing, both at full engine conditions and at engine components level. This article presents the results of engine performance and air pollutant emissions measurements gathered from the alternative fuels qualification testing conducted at the National Research Council Canada over the last seven years. This benchmarking data was collected on various engine platforms at full engine operation at sea level and/or altitude conditions using a variety of aviation alternative fuels and their blends. In order to provide a reference comparison basis, the results collected using the alternative fuels are compared with baseline Jet-A1 or JP-8 conventional fuels.


Author(s):  
Jesus Ortiz-Carretero ◽  
Alejandro Castillo Pardo ◽  
Vassilios Pachidis ◽  
Ioannis Goulos

It is anticipated that the contribution of rotorcraft activities to the environmental impact of civil aviation will increase in the forthcoming future. Due to their versatility and robustness, helicopters are often operated in harsh environments with extreme ambient conditions and dusty air. These severe conditions affect not only the engine operation but also the performance of helicopter rotors. This impact is reflected in the fuel burn and pollutants emitted by the helicopter during a mission. The aim of this paper is to introduce an exhaustive methodology to quantify the influence of the environment in the mission fuel consumption and the associated emissions of nitrogen oxides (NOx). An Emergency Medical Service (EMS) and a Search and Rescue (SAR) mission were used as a case study to simulate the effects of extreme temperatures, high altitude and compressor degradation on a representative Twin-Engine Medium (TEM) weight helicopter, the Sikorsky UH-60A Black Hawk. A simulation tool for helicopter mission performance analysis developed and validated at Cranfield University was employed. This software comprises different modules that enable the analysis of helicopter flight dynamics, powerplant performance and exhaust emissions over a user defined flight path profile. The results obtained show that the environmental effects on mission fuel and emissions are mainly driven by the modification of the engine performance for the particular missions simulated. Fluctuations as high as 12% and 40% in mission fuel and NOx emissions, respectively, were observed under the environmental conditions simulated in the present study.


Author(s):  
I. Roumeliotis ◽  
N. Aretakis ◽  
K. Mathioudakis ◽  
E. A. Yfantis

Any prime mover exhibits the effects of wear and tear over time, especially when operating in a hostile environment. Marine gas turbines operation in the hostile marine environment results in the degradation of their performance characteristics. A method for predicting the effects of common compressor degradation mechanisms on the engine operation and performance by exploiting the “zooming” feature of current performance modelling techniques is presented. Specifically a 0D engine performance model is coupled with a higher fidelity compressor model which is based on the “stage stacking” method. In this way the compressor faults can be simulated in a physical meaningful way and the overall engine performance and off design operation of a faulty engine can be predicted. The method is applied to the case of a twin shaft engine, a configuration that is commonly used for marine propulsion. In the case of marine propulsion the operating profile includes a large portion of off-design operation, thus in order to assess the engine’s faults effects, the engine operation should be examined with respect to the marine vessel’s operation. For this reason, the engine performance model is coupled to a marine vessel’s mission model that evaluates the prime mover’s operating conditions. In this way the effect of a faulty engine on vessels’ mission parameters like overall fuel consumption, maximum speed, pollutant emissions and mission duration can be quantified.


2002 ◽  
Vol 124 (3) ◽  
pp. 636-644 ◽  
Author(s):  
J. M. Desantes ◽  
J. V. Pastor ◽  
J. Arre`gle ◽  
S. A. Molina

To fulfill the commitments of future pollutant regulations, current development of direct injection (DI) Diesel engines requires to improve knowledge on the injection/combustion process and the effect of the injection parameters and engine operation conditions upon the spray and flame characteristics and how they affect engine performance and pollutant emissions. In order to improve comprehension of the phenomena inherent to Diesel combustion, a deep experimental study has been performed in a single-cylinder engine with the main characteristics of a six-cylinder engine passing the EURO III legislation. Some representative points of the 13-mode engine test cycle have been considered modifying the nominal values of injection pressure, injection load, intake pressure, engine speed, and injection timing. The study combines performance and emissions experimental measurements together with heat release law (HRL) analysis and high-speed visualization. Controlling parameters for BSFC, NOx, and soot emissions are identified in the last part of the paper.


2016 ◽  
Vol 138 (10) ◽  
Author(s):  
Nikolaos-Alexandros Vrettakos

The operation during compressor surge of a medium speed marine diesel engine was examined on a test bed. The compressor of the engine's turbocharger was forced to operate beyond the surge line, by injecting compressed air at the engine intake manifold, downstream of the compressor during steady-state engine operation. While the compressor was surging, detailed measurements of turbocharger and engine performance parameters were conducted. The measurements included the use of constant temperature anemometry for the accurate measurement of air velocity fluctuations at the compressor inlet during the surge cycles. Measurements also covered engine performance parameters such as in-cylinder pressure and the impact of compressor surge on the composition of the exhaust gas emitted from the engine. The measurements describe in detail the response of a marine diesel engine to variations caused by compressor surge. The results show that both turbocharger and engine performance are affected by compressor surge and fast Fourier transform (FFT) analysis proved that they oscillate at the same main frequency. Also, prolonged steady-state operation of the engine with this form of compressor surge led to a non-negligible increase of NOx emissions.


2002 ◽  
Vol 124 (3) ◽  
pp. 686-694 ◽  
Author(s):  
D. B. Olsen ◽  
G. C. Hutcherson ◽  
B. D. Willson ◽  
C. E. Mitchell

In this work the tracer gas method using nitrous oxide as the tracer gas is implemented on a stationary two-stroke cycle, four-cylinder, fuel-injected large-bore natural gas engine. The engine is manufactured by Cooper-Bessemer, model number GMV-4TF. It is representative of the large bore natural gas stationary engine fleet currently in use by the natural gas industry for natural gas compression and power generation. Trapping efficiency measurements are carried out with the tracer gas method at various engine operating conditions, and used to evaluate the scavenging efficiency and trapped A/F ratio. Scavenging efficiency directly affects engine power and trapped A/F ratio has a dramatic impact on pollutant emissions. Engine operating conditions are altered through variations in boost pressure, speed, back pressure, and intake port restriction.


2020 ◽  
Vol 8 (10) ◽  
pp. 747
Author(s):  
Vladimir Pelić ◽  
Tomislav Mrakovčić ◽  
Vedran Medica-Viola ◽  
Marko Valčić

The energy efficiency and environmental friendliness of medium-speed marine diesel engines are to be improved through the application of various measures and technologies. Special attention will be paid to the reduction in NOx in order to comply with the conditions of the MARPOL Convention, Annex VI. The reduction in NOx emissions will be achieved by the application of primary and secondary measures. The primary measures relate to the process in the engine, while the secondary measures are based on the reduction in NOx emissions through the after-treatment of exhaust gases. Some primary measures such as exhaust gas recirculation, adding water to the fuel or injecting water into the cylinder give good results in reducing NOx emissions, but generally lead to an increase in fuel consumption. In contrast to the aforementioned methods, the use of an earlier inlet valve closure, referred to in the literature as the Miller process, not only reduces NOx emissions, but also increases the efficiency of the engine in conjunction with appropriate turbochargers. A previously developed numerical model to simulate diesel engine operation is used to analyse the effects of the Miller process on engine performance. Although the numerical model cannot completely replace experimental research, it is an effective tool for verifying the influence of various input parameters on engine performance. In this paper, the effect of an earlier closing of the intake valve and an increase in inlet manifold pressure on fuel consumption, pressure and temperature in the engine cylinder under steady-state conditions is analysed. The results obtained with the numerical model show the justification for using the Miller processes to reduce NOx emissions and fuel consumption.


1999 ◽  
Vol 43 (04) ◽  
pp. 201-217
Author(s):  
P. Chesse ◽  
B. Inozu ◽  
P. Roy ◽  
X. Tauzia ◽  
J. F. Hetet

This paper describes a diesel engine simulation code, named SELENDIA, jointly developed by EcoleCentrale de Nantes, France, and the University of New Orleans. The adopted models for steady-state and transient response simulation are briefly introduced in addition to various validation results. The capabilities of the code are illustrated by a study regarding the transient response of a sequentially turbocharged marine diesel engine as well as the simulation of engine performance under extreme conditions and the investigation of engine pollutant emissions.


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