The Effect of Air Throttle on Combustion Process and Emission Formation in Marine Lean-Burn Gas Engines

Abstract

Enhancing the marine propulsion system's performance is one of the crucial issues that has received noteworthy attention due to the current strict emission legislation. A fundamental improvement without an additional after-treatment system is employing natural gas fuel in lean-burn combustion. Lean combustion may improve the thermal efficiency in a stable condition, but a real ship works in a time-varying inflow on the propeller, and the engine must afford high-efficiency combustion against the fluctuating load. Stable combustion in a lean-burn marine gas engine is guaranteed by installing controllers on the air and the fuel pipes to regulate airfuel ratio and engine speed. The present study aimed to investigate the influence of adding an air throttle during the engine's lower loads and its effectiveness during a time-varying load. A thermodynamics model of spark ignition engine with an imposed constant and transient load is presented. The results revealed that using a throttle in the lower loads may improve the engine fuel consumption and emission formation during steady-state, but, in transient condition, it showed a negligible impact on the brake specific fuel consumption and unburned hydrocarbon emission formation.

Transient Performance of Gas-Engine-Based Power System on Ships: An Overview of Modeling, Optimization, and Applications

“…This approach stands for a general pathway to enhance the control accuracy of the air-fuel ratio and to improve the load response of the combustion engine itself, making it applicable to both diesel and gas engines for fixed and variable speed applications. However, as studied in [95], the real sea conditions with high-frequency fluctuations cannot be followed when using only an air throttle in gas engines due to its angle delay. Consequently, more measures have been investigated and discussed to increase the air supply ability in engines, especially for the turbocharger system, and their control strategies [94].…”

“…From the perspective of the turbocharger structure, the goal of these studies is to increase boost pressure and air mass flow during the running. Before developing advanced turbochargers to increase air-boosting ability, it should be noted that the reason leading to the time delay is the rotational inertia of the turbine and compressor, as discussed in [96,97]. The mass of the turbocharger determines the rotational inertia and the ability to prevent speed variation during varying loads and reduce the transient performance of engines.…”

“…It can be seen from the MAPs that the turbocharger speed determines the air mass flow, and its time delay dominates the engine response ability. Similar to the crankshaft rotation dynamic, the turbocharger speed dynamic can also be modeled based on Newton's second law by introducing the inertia, whose effect on the engine load response has been proven in [96,97]. A summary of the physical-based modeling of the engine components is listed in Table 3.…”

“…At present, this method enjoys the widest acceptance in transient situation studies. This method has been implemented in GT-Power and, then, was integrated into various loading scenarios to investigate the engine performance and test the control strategies [65,95,166,[207][208][209][210][211][212]. One-dimensional simulation has also been developed on another platform; Marco et al [115] established the dual-fuel gas engine model for comparing the influence of the turbocharger on engine power management based on the Matlab/Simulink environment.…”

Fuel consumption and emission reduction of marine lean-burn gas engine employing a hybrid propulsion concept

“…13 Stable combustion in a lean-burn marine gas engine is supported by rapid feedback controllers on air and fuel passages to adjust the air-fuel ratio and engine speed, but the controllers do not adequately provide the feedback to control the combustion during rapid load changes. 14 Therefore, part of the fuel crosses into the exhaust manifold during the load reduction of transient sea conditions. Furthermore, a remarkable rise of NO X formation occurs during load increase.…”