A Two-Zone Combustion Model for Knocking Prediction of Marine Natural Gas SI Engines

Abstract

The further thermal efficiency improvement of marine natural gas engine is constrained by a knocking phenomenon that commonly occurs in gas-fueled spark-ignited engines. It plays an important role to investigate how the knocking occurs and how to predict it based on the engine simulation model. In this paper, a two-zone model is developed to provide the prediction of knocking performance and NO emission, which is verified by engine test bed data from a transformed marine natural gas spark ignition (SI) engine. Cylindrical division theory is used to describe the shape of the two zones to decrease the computational cost, as well as a basic mechanism for NO concentration calculation. In order to solve the volume balance, three boundary parameters are introduced to determine the initial condition and mass flow between the two zones. Furthermore, boundary parameters' variation and knocking factor (compression ratio and advanced ignition angle) will be discussed under different working conditions. Result shows that the two-zone model has sufficient accuracy in predicting engine performance, NO emission and knocking performance. Both the increasing compression ratio and advanced ignition angle have a promoting effect on knocking probability, knocking timing and knocking intensity. The knocking phenomenon can be avoided in the targeted natural gas SI engine by constraining the compression ratio smaller than 14 and advanced ignition angle later than 30 • before top dead center (BTDC).Energies 2018, 11, 561 2 of 23 Two broad categories of experimental based methods are used to detect the knocking phenomenon in a certain natural gas engine: the former one is based on direct measurement, like an intensified charge coupled detector (ICCD) camera and Laser-induced Fluorescence (LIF) imaging [8,9]; other methods [10,11] are based on indirect measurement such as in-cylinder pressure analysis, cylinder block vibration, exhaust gas temperature, etc. On the other hand, simulation models enable engineers to explore the details comprehensively during the design period in order to determine the best case, saving research time and development cost. In general, numerical simulation of the natural gas engine working process is classified as follows: the mean value model, zero-dimensional model, quasi-dimensional model and multi-dimensional model [12]. The mean value model is not primarily intended for engine development, but it is efficient for integrated system research, thus it is usually based on a large amount of engine test data and has scarcely no ability to predict [13,14]. For knocking prediction simulation models, the main objective is to characterize the end-gas temperature, which has a direct effect on knocking occurring. It is difficult for the zero-dimensional model to achieve this goal since the in-cylinder temperature and species concentrations are assumed to be uniform throughout the cylinder [15]. The multi-dimensional simulation model (or Computational Fluid Dynamics model, CFD) provides most details of in-cylinder para...

A Zero-Dimensional Mixing Controlled Combustion Model for Real Time Performance Simulation of Marine Two-Stroke Diesel Engines

“…where, k * is a model constant, which is optimized to a certain nozzle and set at 0.6514 here; M(t) is the integration of momentum flow of the fuel injection calculated by Equation (23).…”

“…Wiebe's function is one of the widely used combustion models in working process and engine performance simulation [20,21]. Moreover, the parameters of Wiebe's function are optimized by applying experimental data and adjustable corresponding to the changing of the running conditions of the engine [22,23]. However, more and more parameters, such as injection timing, injection profile, multi-injection, and optimization of CA50, etc., of the fuel injection system of the sophisticated engine can be controlled by the ECU (engine control unit).…”

“…Wiebe's function cannot fully provide these flexibilities. Therefore, various zero-dimension combustion models, most of which usually couple with the emission model of NOx, are applied in many cases [12,23,24].…”

Effect of Pre-Combustion Chamber Nozzle Parameters on the Performance of a Marine 2-Stroke Dual Fuel Engine

“…Natural gas, as a clean energy source, has the advantages of higher heating value and lower price-making the marine 2-stroke low-speed gas engines which use it as a fuel significantly economical [5,6]. In addition, the natural gas is free of sulfur, which means that there is almost no formation of Sulfur Oxides (SOx) [7]. However, when natural gas is used as the only fuel of the engine, the power of the gas engine will decrease compared to the same size diesel engine [8].…”

An Experimental Investigation into Combustion Fitting in a Direct Injection Marine Diesel Engine

“…Fang et al built a two-dimension combustion model to study the effect of electric fields on the combustion characteristics of a lean-burning methane air mixture [19]. Xiang et al proposed a two-zone combustion model in nature gas engine application and used this model for engine knocking predictions [20].…”