Finite element based fatigue life prediction of cylinder head for two-stroke linear engine using stress-life approach

Abstract: This describes the finite element based fatigue life prediction of cylinder head for two-stroke linear engine subjected to variable amplitude loading applicable to electric power generation. A set of Al-alloys, cast iron and forged steel for cylinder head are considered in this study

In-cylinder heat transfer characteristics of hydrogen fueled engine: a steady state approach

Abstract: This study presents in-cylinder heat transfer characteristics of a single cylinder port injection Hydrogen fueled Internal Combustion Engine (H2ICE) using a steady state approach. Problem statement: The differences in characteristics between hydrogen and hydrocarbon fuels are led to the difference in the behavior of physical processes during engine cycle. One of these processes is the in-cylinder heat transfer. Approach: One dimensional gas dynamic model was used to describe the heat transfer characteristics of the engine. The engine speed was varied from 2000-5000 rpm, crank angle from -40° to +100°, while Air-Fuel Ratio (AFR) was changed from stoichiometric to lean limit. Results: The simulated results showed higher heat transfer rate but lower heat transfer to total fuel energy ratio with increasing the engine speed. The in-cylinder pressure and temperature were increased with decreasing AFR and increasing engine speed. The in-cylinder air flow rate was increased linearly with increasing engine speed as well as air fuel ratio. Conclusion/Recommendations: The results showed that the AFR has a vital effect on characteristics variation while the engine speed has minor effect. These results can be utilized for the study of combustion rocess, fuel consumption, emission production and engine performance

Cycle Analysis of In-cyclinder Heat Transfer Characteristics for Hydrogen Fueled Engine

The overall heat transfer process within the in-cylinder for port injection hydrogen fueled internal combustion engine (H2ICE) was investigated. One-dimensional gas dynamics was used to describe the flow and heat transfer in the components of the engine model. The engine model was simulated with a variable injection timing, engine speed and equivalence ratio (φ). Simulation was executed for 60 deg ATDC ≤ θinj ≤ 160 deg ATDC (during the intake stroke), 1000 ≤ rpm ≤ 6000 and 0.2 ≤ φ ≤ 1.2. The experimental data were utilized for validation purpose of the adopted numerical model. The baseline engine model with gasoline fuel was verified with experimental data, and reasonable agreement has been achieved. The overall results show that there is a combined influence for the engine speed and equivalence ratio on the overall heat transfer characteristics. The identification for the effect of the injection timing on the overall heat transfer characteristics has been failed because the injection issue is not considered within the combustion approach

Throttling effect on the performance and emissions of a multi-cylinder gasoline fuelled spark ignition engine

The throttle mechanism, a regulatory technique of engine output, is accompanied by a loss of some energy. The effect of intake air throttling on the performance and emissions of a multi-cylinder spark ignition gasoline engine was experimentally investigated. The engine was coupled to a hydraulic dynamometer equipped with a customized cooling system for both the engine and dynamometer. Experimental tests were performed for various engine speeds and air-fuel ratios at the WOT and POT conditions with optimized ignition timing. The acquired results recorded that a better engine operation could be achieved with WOT in terms of bmep, bsfc, ηb, CO, CO2 and UHC compared to POT. At the same time, the worst trend at WOT was noticed for the NOx concentration due to the higher conversion efficiency of fuel combustion. In terms of engine speed for both WOT and POT conditions, operating at 3000 rpm represents the minima of ϕ, bsfc, CO and UHC; and the maxima of ηb, CO2 and NOx with some fluctuation on both sides of this point. Maximum recorded values of ηb were about 30.55% and 28. 55%, while the minimum values of bsfc were about 274 and 293 g/kW.h for the WOT and POT conditions, respectively. The maximum bmep was obtained at 2500 rpm at WOT and POT conditions with values of about 940 kPa and 904 kPa, respectively. Maximum recorded values of NOx were about 1525 and 977 ppm for the WOT and POT conditions, respectively

Burnout among surgeons before and during the SARS-CoV-2 pandemic: an international survey

Background: SARS-CoV-2 pandemic has had many significant impacts within the surgical realm, and surgeons have been obligated to reconsider almost every aspect of daily clinical practice. Methods: This is a cross-sectional study reported in compliance with the CHERRIES guidelines and conducted through an online platform from June 14th to July 15th, 2020. The primary outcome was the burden of burnout during the pandemic indicated by the validated Shirom-Melamed Burnout Measure. Results: Nine hundred fifty-four surgeons completed the survey. The median length of practice was 10 years; 78.2% included were male with a median age of 37 years old, 39.5% were consultants, 68.9% were general surgeons, and 55.7% were affiliated with an academic institution. Overall, there was a significant increase in the mean burnout score during the pandemic; longer years of practice and older age were significantly associated with less burnout. There were significant reductions in the median number of outpatient visits, operated cases, on-call hours, emergency visits, and research work, so, 48.2% of respondents felt that the training resources were insufficient. The majority (81.3%) of respondents reported that their hospitals were included in the management of COVID-19, 66.5% felt their roles had been minimized; 41% were asked to assist in non-surgical medical practices, and 37.6% of respondents were included in COVID-19 management. Conclusions: There was a significant burnout among trainees. Almost all aspects of clinical and research activities were affected with a significant reduction in the volume of research, outpatient clinic visits, surgical procedures, on-call hours, and emergency cases hindering the training. Trial registration: The study was registered on clicaltrials.gov "NCT04433286" on 16/06/2020

Parametric Study Of Instantaneous Heat Transfer Based on Multidimensional Model in Direct-Injection Hydrogen-Fueled Engine

This paper presents a parametric study on instantaneous heat transfer of a direct-injection hydrogen-fueled engine using a multidimensional model. A simplified single-step mechanism was considered for estimating the reaction rate of hydrogen oxidation. The modified wall-function was used for resolving the near-wall transport. An arbitrary Lagrangian–Eulerian algorithm was adopted for solving the governing equations. Experimental measurements were implemented to verify the developed model. They show that the instantaneous heat-transfer model is sufficiently accurate. The influence of engine speed, equivalence ratio, and the start of injection timing were investigated. The flow fields appeared to have greater size vectors and coarser distribution with an increase of engine speed. A heterogeneous distribution was obtained for an ultra-lean mixture condition (φ ≤ 0.5), which decreased with an increase of equivalence ratio. There was no pronounced influence of the start of injection on the flow field pattern and mixture homogeneity. Thermal field analysis was used to demonstrate trends in the instantaneous heat transfer. It was observed that there was a crucial distinction between the lean and ultra-lean mixtures as well as the engine speed. Furthermore, a non-uniform behavior was found for the impact of the equivalence ratio on temperature distribution. It is clear that the developed models are powerful tools for estimating the heat transfer of the hydrogen-fueled engine. The developed predictive correlation is highly accurate in predicting the heat transfer of the hydrogen-fueled engine, focusing on the equivalence ratio as a governing variable

Numerical Investigation of In-Cylinder Flow Characteristics of Hydrogen-Fuelled Internal Combustion Engine

This paper addresses the computational fluid dynamics (CFD) simulation to investigate the in-cylinder flow characteristics of 2D combustion chamber for a hydrogen-fuelled four-stroke internal combustion engine. CFD simulation has been carried out using commercial CFD codes. The engine speed was varied from 1000 to 3000 rpm, the range of equivalent ratio from 0.6 to 1.0 and the crank angle from 0 to 720 degrees in this study. The effect of the engine speed and equivalence ratio on the flow-field characteristics and volumetric efficiency are investigated in the motoring condition. The increase of engine speed gives a more efficient diffusion process for hydrogen and gives a more homogeneous air–fuel mixture structure. The characteristics of the flow-field are represented by the in-cylinder pressure and temperature distribution as well as the contours of the hydrogen mass fraction for different engine speeds. The acquired results show the maximum in-cylinder temperature and pressure obtained of 650 K and 1.143 MPa at the engine speed of 3000 rpm respectively. It can be seen that the engine speed and equivalence ratio are strongly related to the volumetric efficiency. The results show that the volumetric efficiency increases linearly with increase of the engine speed, but decreases with increase of the equivalence ratio. The results obtained from the simulation can be employed to examine the homogeneity of the air–fuel mixture structure for a better combustion process and engine performance

Heat transfer of intake port for hydrogen fueled port injection engine: A steady state approach

The steady state heat transfer analysis of intake port for hydrogen fueled port injection engine is investigated. One dimensional gas dynamics was described by the flow and heat transfer in the components of the engine model. The engine model is simulated with variable engine speed and equivalence ratio (φ). Engine speed varied from 2000 to 5000 rpm with increment of 1000 rpm, while equivalence ratio changed from stoichiometric to lean limit. The effects of equivalence ratio and engine speed on heat transfer characteristics for the intake port are presented in this paper. The baseline engine model is verified with existing previous published results. Comparison between hydrogen and methane fuel was made. The obtained results show that the engine speed has the same effect on the heat transfer coefficient for hydrogen and methane fuel, while equivalence ratio has effect on heat transfer coefficient in case of hydrogen fuel only. Rate of increase in heat transfer coefficient comparison with stoichiometric case for hydrogen fuel are: 4% for (φ = 0.6) and 8% for (φ = 0.2). While negligible effect was found in case of methane fuel with change of equivalence ratio. But methane is given greater values about 11% for all engine speed values compare with hydrogen fuel under stoichiometric condition. The blockage phenomenon affected the heat transfer process dominantly in case of hydrogen fuel; however, the forced convection was influencing the heat transfer process for hydrogen and methane cases

Characterization Of The Time-Averaged Overall Heat Transfer In A Direct-Injection Hydrogen-Fueled Engine

This paper presents a description of the time-averaged heat transfer in a direct-injection hydrogen-fueled engine. A computer simulation of the overall heat transfer process within the in-cylinder was run. The experimental results were used to validate the adopted numerical model. One-dimensional gas dynamics were used to describe the flow and heat transfer in the components of the engine model. The engine model was simulated while varying the engine speed, equivalence ratio (φ), and start of injection (SOI) timing, respectively, as follows: 1800 ≤ rpm ≤ 5000, 0.2 ≤ φ ≤ 1.2, and 130° ≤ SOI ≤ 70° before top dead center. The baseline model of the hydrogen-fueled engine was verified through the experimental results, and reasonable agreement was achieved. The results show that the equivalence ratio has a significant impact on the time-averaged heat transfer characteristics. This is a unique behavior that appears in the case of hydrogen-fueled engines due to the wide flammability range. Delaying the injection timing caused different behavior of the time-averaged characteristics of heat transfer. This is an indication of remarkably poor combustion because there is insufficient time for fuel injection before the initiation of the combustion process

Time-averaged Heat Transfer Correlation for Direct Injection Hydrogen Fueled Engine

This paper presents the development of an empirical correlation for the prediction of time averaged heat transfer for a direct-injection hydrogen fueled engine. Computer simulation based on one-dimensional gas dynamics approach was used to perform the time-averaged analysis for the in-cylinder heat transfer. Simulation was performed for 1800 < rpm < 5000, 0.2 < 4 < 1.2 and 130 deg before top dead center (BTDC) < SOI < 70 deg BTDC. Experimental measurements were used to verify the developed model, during which the engine performance could be determined to a reasonable accuracy of 10%. The equivalence ratio (4) was considered as a governing variable, through the new correlation for the time averaged heat transfer. A nonlinear regression approach was used to develop the new correlations. In the case of all the simulation data, the proposed correlations have a satisfactory performance with the determination coefficient (R2) of about 0.99. A relative error of 10% was found in more than 95% of the simulation data. However, the relative error was reduced to about 50% in the newly developed correlations, which increased its reliability to more than the Taylor’s correlation for representing the actual data. Due to the general form, hydrocarbon fuel is suitable for the newly developed correlations that are theoretically made