Techno-economical analysis of single pressure exhaust gas waste heat recovery systems in marine propulsion plants

In this article, the waste heat recovery (WHR) installations used for the production of saturated steam and electric power for the cases of a two-stroke and a four-stroke engine propulsion plant of a typical merchant ship are investigated. The examined WHR system is considered to be of the single steam pressure type with an external heat exchanger for the heating of feed water entering into the boiler drum. The option of using the engine air cooler for heating the feed water was also examined. The WHR installation was modeled under steady-state conditions, and the derived WHR installation parameters for various engine loads are presented and analyzed. Furthermore, using the simulation results, the improvement of Energy Efficiency Design Index (EEDI) of the examined ship is calculated, and the impact of the WHR on the ship EEDI is discussed. In addition, following the technical evaluation of the alternative options for the ship propulsion plant, an economic study was performed for a typical ship voyage. The derived results were presented and discussed leading to conclusions for the most techno-economical propulsion system configuration

Techno-economic investigation of alternative propulsion plants for ferries and RoRo ships

In this paper, the main alternative propulsion plants based on reciprocating internal combustion engines of a ferry or RoRo ship operating in routes that include Emission Control Areas (ECAs) are comparatively assessed. Specifically, a dual fuel engine propulsion plant is compared with a conventional Diesel engine plant. For both cases, the installation of a Waste Heat Recovery system, which covers a part of the ship electric energy demand, is also considered. The ship main DF engines are assumed to operate using LNG and a small amount of MDO for initiating combustion, whereas low sulphur MDO was regarded as the fuel for the case of the Diesel engine plant. The installation of selective catalytic reduction (SCR) after-treatment unit for reducing the NOx emissions for the case of Diesel engines plant is also taken into account. The propulsion plants were modelled under steady state conditions, and the simulation results were analysed in order to compare the alternative configurations. Furthermore, the energy efficiency design index (EEDI) values were calculated and the two examined propulsion system cases were compared on EEDI basis. Finally, the Life Cycle Cost for each alternative propulsion plant was calculated and used for completing an economic evaluation of the Dual fuel propulsion plant versus the conventional designs applied in ferries

Open type ferry safety systems design for using LNG fuel

This feasibility study investigates the viability of employing Liquefied Natural Gas (LNG) fuel to an open type Ro-Ro passenger ferry and the potential challenges imposed with regard to the vessel safety systems. The study proposes appropriate methodology for converting the existing ship to run on LNG fuel and discusses all the necessary modifications to the ship’s safety systems; furthermore, the ship’s evacuation analysis is investigated accordingly. The basic requirements that the ship already complies with are initially reported for each safety system while the additional restrictions that need to be taken into consideration for employing LNG fuel are analysed; appropriate actions are proposed. Furthermore, a Hazard Identification Study (HAZID) is also carried out. Overall, the technical feasibility of the investigated scenario is clearly demonstrated; minimal modifications to the ship's safety systems in order to comply with the imposed safety rules are required for the specific type of ship

A novel method for safety analysis of Cyber-Physical Systems - Application to a ship exhaust gas scrubber system

Cyber-Physical Systems (CPSs) represent a systems category developed and promoted in the maritime industry to automate functions and system operations. In this study, a novel Combinatorial Approach for Safety Analysis is presented, which addresses the traditional safety methods’ limitations by integrating System Theoretic Process Analysis (STPA), Events Sequence Identification (ETI) and Fault Tree Analysis (FTA). The developed method results into the development of a detailed Fault Tree that captures the effects of both the physical components/subsystems and the software functions’ failures. The quantitative step of the method employs the components’ failure rates to calculate the top event failure rate along with criticality analysis metrics for identifying the most critical components/functions. This method is implemented for an exhaust gas open loop scrubber system safety analysis to estimate its failure rate and identify critical failures considering the baseline system configuration as well as various alternatives with advanced functions for monitoring and diagnostics. The results demonstrate that configurations with SOx sensor continuous monitoring or scrubber unit failure diagnosis/prognosis lead to significantly lower failure rate. Based on the analysis results, the advantages/disadvantages of the novel method are also discussed. This study also provides insights for better safety analysis of the CPSs

Effectiveness of Treadmill Training on Walking Ability in Adults with Cerebral Palsy: A Systematic Review and Meta-Analysis

Background: Patients with cerebral palsy (CP) may necessitate long-term treatment and monitoring of their condition, not only during the period of development but also during adulthood. Objectives: This systematic review aimed to analyze evidence from randomized controlled trials (RCTs) that have investigated the effect of treadmill training on walking ability in adults with cerebral palsy. Methods: RCTs were identified and selected systematically, with appropriate keywords applied in four scientific databases (Medline, Scopus, the Cochrane Library, and the Physiotherapy Evidence Database) and one bibliographic search engine (Google Scholar) from January 1980 to September 2021. Two assessors extracted and analyzed data from relevant RCTs published in English and then independently rated those studies for risk of bias with the Risk of Bias (RoB 2) tool. Results: Out of the 96 studies that were initially identified, 93 were excluded, as these either did not meet the inclusion criteria or were duplicates. Three clinical trials were finally included, characterized by some concerns and a high risk of bias (RoB 2). Meta-analysis was only performed for the maximum distance in the ‘6-minute walk for distance test’, due to differences in the remaining outcomes utilized between studies. Overall, there was evidence of some concerns and high risk of bias that treadmill training did not significantly improve the walking ability in adult patients with CP relative to the control conditions. Conclusion: More high-quality RCTs are required, examining the effectiveness of treadmill training on different aspects of walking ability such as gait speed, endurance, and energy expenditure

A decision support system for the development of voyage and maintenance plans for ships

The waterborne sector faces nowadays significant challenges due to several environmental, financial and other concerns. Such challenges may be addressed, among others, by optimising voyage plans, and diagnosing as early as possible engine failures that may lead to performance degradation. These two issues are addressed by the Decision Support System (DSS) presented herein, which focuses on the operation of merchant ships. For the development of voyage plans, a multicriteria decision problem is developed and handled with the PROMETHE method, while a multivariable control chart is used for the fault diagnosis problem. A MATLAB-based software implementation of the DSS has been developed adopting a modular architecture, while, in order to provide a generic software solution, the required input data are retrieved from dedicated web-services, following specific communication and data exchange protocols

A combinatorial safety analysis of cruise ship Diesel-Electric Propulsion plant blackout

Diesel-Electric Propulsion (DEP) has been widely used for propulsion of various ship types including cruise ships. Considering the potential consequences of blackouts, especially on cruise ships, it is essential to design and operate the ships power plants for avoiding and preventing such events. This study aims at implementing a comprehensive safety analysis for a cruise ship Diesel-Electric Propulsion (DEP) plant focusing on blackout events. The Combinatorial Approach to Safety Analysis (CASA) method is used to develop Fault Trees considering the black out as the top event, and subsequently estimate the blackout frequency as well as implement importance analysis. The derived results demonstrate that the overall blackout frequency is close to corresponding values reported in the pertinent literature as well as estimations based on available accident investigations. This study deduces that the blackout frequency depends on the number of operating Diesel Generators (DG) sets, the DG sets loading profile, the amount of electrical load that can be tripped during overload conditions and the plant operation phase. In addition, failures of the engine auxiliary systems and the fast-electrical load reduction functions as well as the power generation control components are identified as important. This study demonstrates the applicability of the CASA method to complex marine systems and reveals the parameters influencing the investigated system blackout frequency, thus providing better insights for these systems safety analysis and enhancement

Marine dual fuel engine modelling and parametric investigation of engine settings effect on performance-emissions trade-offs

The continuous stringent requirements of the environmental regulations along with the LNG fuel penetration and the development of port and bunkering facilities, render the use of the dual fuel engines an attractive alternative of the traditional ship propulsion plants based on Diesel engines running with HFO for reducing both the plant operating cost and environmental footprint. The present study deals with the computational investigation of a large marine dual fuel (DF) engine of the four-stroke type for comparing its performance and emissions, in both diesel and gas mode operation by using the commercial software GT-ISE. The engine diesel model was initially set up and calibrated to adequately represent the engine operation. Subsequently, the engine dual fuel model was further developed by considering the injection of two different fuels; methane in the cylinder inlet ports and pilot diesel fuel into the engine cylinders. The derived results were analysed for revealing the differences of the engine performance and emissions at each operating mode. In addition, the turbocharger matching was investigated and discussed to enlighten the turbocharging system challenges due to the completely different air−fuel ratio requirements in diesel and gas modes, respectively. Finally, parametric simulations were performed for gas mode operation at different loads by varying pilot fuel injection timing, inlet valve closing and inlet manifold boost pressure, aiming to identify the engine settings that simultaneously reduce CO2 and NOx emissions considering the air−fuel ratio operation window limitations. The parametric study results are discussed to infer the engine optimal settings

Comparative assessment of alternative propulsion systems of ferries operating in ECAs

The objective of this paper is to comparatively assess four main alternative propulsion plants based on reciprocating internal combustion engines of a typical ferry or Ro-Ro ship operating in routes that include Emission Control Areas (ECAs). Specifically, the dual fuel (DF) engine propulsion plant is compared with a conventional Diesel engine plant. The cases of the installation of a Waste Heat Recovery (WHR) system are also investigated. The propulsion plants were modelled under steady state conditions, and the simulation results were analysed in order to compare the various configurations. Furthermore, using the simulation results, energy efficiency design index (EEDI) values for each case are calculated and the propulsion plants compliance with the respective IMO regulations is discussed. Then, the annual cost including investment and operational for each alternative propulsion plant is calculated for two ship sailing scenarios; the first considers the ship partly sailing inside Emission Control Areas (ECAs), whereas the other considers the ship sailing entirely within ECAs. The results are used for performing the economical evaluation of the examined propulsion plants. Finally, the annual carbon dioxide emissions are estimated and used for comparing the propulsion plant alternative solutions

Accurate instantaneous engine speed recording by employing an optical measurement system-application to a typical low power industrial engine

The presented work concerns the development of a novel measurement system for determining the instantaneous rotational speed of an engine with high accuracy. The developed system is mainly based on a commercially available optical sensor and appropriate data acquisition / post-processing procedure. The accuracy of the system is high; speed recording with a resolution of one degree of crank angle has been succeeded when measuring the speed of a one cylinder four stroke S.I. motored engine. The deduced experimental results were compared with the corresponding theoretical ones obtained by appropriate simulations, validating the proper functionality of the developed system. Furthermore, the system was also integrated into a typical four cylinder low power industrial engine successfully. Key-features of the proposed measurement configuration are accuracy, simplicity and low-cost suggesting numerous potential applications