Comparative Assessment and Parametric Optimisation of Large Marine Two-Stroke Engines with Exhaust Gas Recirculation and Alternative Turbocharging Systems

Daoyi Lu,Gerasimos Theotokatos,Hong Zeng,Keying Cui,Jundong Zhang

doi:10.3390/jmse10030351

Abstract

Although the exhaust gas recirculation (EGR) technology has been proven effective to decrease the marine engine’s nitrogen oxides (NOx) emissions, it is associated with a considerable fuel consumption increase and challenges to the engine–turbocharger matching. This study aims to parametrically optimise the EGR and turbocharging system settings of a large marine two-stroke engine with the objective of obtaining the highest engine efficiency whilst ensuring compliance with the prevailing NOx emissions limits. Two typical configurations of the investigated engine (baseline and alternative) are modelled in the GT-SUITE software. Parametric simulations are performed with EGR rates up to 40% along with cylinder bypass rates up to 50%, and the simulation results are analysed to quantify the impact of the engine operation with EGR on the performance and NOx emissions parameters. For the baseline engine configuration, the EGR rate increase considerably deteriorates the brake specific fuel consumption (BSFC), which is attenuated by opening the cylinder bypass valve. The optimal combinations of the EGR and cylinder bypass rates for each operating point are identified for both configurations. Following the comparative assessment between the two engine configurations, recommendations for the engine operating modes are proposed, leading to BSFC improvement in the region of 0.7 to 2.9 g/kWh. This study provides insights for the operational settings optimisation of two-stroke engines equipped with EGR systems, contributing towards the reduction of the associated environmental carbon footprint.

Highlights

Maritime transport underpins global supply chain linkages and economic interdependency, with shipping being estimated to handle over 80% of global merchandise trade [1].The reduction of exhaust gas emissions from shipping operations has increasingly become a topic of public interest [2]
The most stringent nitrogen oxides (NOx) Tier III emission limits (TIII limits) that are implemented in Emission Control Areas (ECAs) [5] are reduced by about 80% compared to the Tier I limits
It is an immense challenge for shipowners to achieve these high NOx reduction ratios while not impacting the engine fuel economy, which is associated with the carbon emissions and the brake specific fuel consumption (BSFC) [6,7]

Summary

Introduction

Maritime transport underpins global supply chain linkages and economic interdependency, with shipping being estimated to handle over 80% of global merchandise trade [1].The reduction of exhaust gas emissions from shipping operations has increasingly become a topic of public interest [2]. Due to the adverse effects of the nitrogen oxides (NOx) on the environment and human health [3], the issue of marine engines NOx emissions reduction gained considerable attention by the governments and related organisations. The most stringent NOx Tier III emission limits (TIII limits) that are implemented in Emission Control Areas (ECAs) [5] are reduced by about 80% compared to the Tier I limits. It is an immense challenge for shipowners to achieve these high NOx reduction ratios while not impacting the engine fuel economy, which is associated with the carbon emissions and the brake specific fuel consumption (BSFC) [6,7]

Objectives

Methods

Results

Conclusion