CC BY
22
https://doi.org/10.29013/AJT-21-7.8-18-21
Madey Volodymyr Vasilevich, Postgraduate, National University Odessa Maritime Academy
Odessa, Ukraine
E-mail: [email protected]; [email protected]
USAGE OF BIODIESEL IN MARINE DIESEL ENGINES
Abstract. The technology of using biodiesel fuel in marine diesel engines is considered. The diagram of the fuel system using biodiesel fuel is shown. It has been experimentally established that the use of biodiesel fuel provides a decrease in the concentration of nitrogen oxides in exhaust gases by 7.7 ... 23.8%, while the specific fuel consumption increases by 1.5 ... 3.9%.
Keywords: marine medium-speed diesel, fuel system, biodiesel, environmental performance of diesel.
The main energy source for heat engines (gas turbines, boilers, diesels) is oil-based fuel. According to British Petroleum's 2020 data, the world's proven oil reserves are estimated at 244.6 billion tonnes. Considering the yearly fuel consumption volumes, the world power industry has enough of such resources for 40-45 years [1; 2]. This, together with the present-day ecological requirements for heat engines, imposes the development of alternative power engineering and the development of alternative fuels [3].
Fuels for marine diesel engines are traditionally divided into heavy and light ones. To the first category belong fuels, viscosity of which at 50 °C exceeds 50 sSt (in modern diesel engines are used fuels with viscosity up to 500...700 sSt). Light fuels are characterised by viscosity of 2.40 sSt. Heavy fuel (compared to light) contains high levels of sulphur (up to 0.5%) and nitrogen (up to 1.0%). Their combustion produces toxic components - sulphur oxides SOX and nitrogen oxides NOX, which have a negative effect on the environment and people. Therefore, specific tasks of ship power plant operation include prevention of formation and neutralization of environmentally hazardous substances formed at usage of oil diesel fuel. Therefore, recently great attention is paid to reduction of harmful substances in combustion products, especially NOx [4; 5]. In order to
reduce the concentration of these substances different methods and technologies are used: injection of water into the air and exhaust manifold and directly into the diesel cylinder; exhaust gas recirculation, use of alternative fuel which is cheap, calorific and environmentally friendly [6; 7].
In the last decades extensive studies of the possibility of alternative fuels application are carried out [8; 9]. Partial substitution of traditional engine fuels by synthetic liquid hydrocarbons obtained from natural gas and by biodiesel fuels obtained from vegetable oils are considered to be the best [10; 11].
The research task was to determine the influence of alternative fuels on economical and ecological performance of a diesel engine.
Application of alternative fuels for higher power marine diesel engines (with cylinder diameter of over 0.4.0.42 m and nominal power over 5000 kW) is limited due to the following facts uncontrolled deterioration of environmental performance (due to fluctuations in fuel-air ratio) [12];
- torque reduction (due to a fall in maximum cycle pressure) [13]; - reduction of;
- Decrease in effective power at nominal load (due to change in fuel period) [14].
Small and medium power internal combustion engines of vessels (with cylinder diameter up to 0.32-
0.36 m and nominal power not exceeding 3000 kW) are used as auxiliary engines (transferring power to the electric generator). There are 2-4 such engines, each having its own fuel system, so it allows using fuels with different characteristics (including alternative fuels) for providing operation cycle [15; 16].
As a rule diesel engines are not run solely on alternative fuels. These fuels have lower viscosity, and their lower calorific value doesn't allow to obtain energy necessary for piston displacement and shaft rotation. Therefore, mixtures of traditional and alternative fuels are used in marine power generation. The easiest way to add alternative fuel to traditional fuel is directly in the ship's fuel system, before the fuel mixture is fed
into the diesel engine cylinder. Concentration of alternative fuel in the fuel mixture is 5.. .30% [17].
The research was performed on 6H17/28 Hyundai Heavy Industries medium-speed marine diesel engines with the following main characteristics: bore - 0.17 m; stroke - 0.28 m; speed - 900 rev/min; output range - 690 kW; cylinders - 6.
Three such diesels were part of the power plant of a seagoing vessel of 14,745 tonnes deadweight. A schematic of the diesel fuel system is shown in (Figure 1).
Figure 1. Schematic diagram of the fuel system of 6H17/28 Hyundai Heavy Industries marine diesel engines: 1 - fuel pump; 2, 5 - fuel filter; 3 - flow meter; 4 - dispenser; 6 - fuel line; 7 - waste tank
The fuel circuit to the first diesel was not changed and the diesel was operated with DMA fuel (with a viscosity of 6 sSt and 0.08% sulphur content). The fuel viscosity allows the addition of biodiesel (with a viscosity of 5 sSt and a sulphur content of0.005%). The biodiesel content in the fuel mixture was varied in the range 5.20%. The fuel mixture was fed to diesels 2 and 3. In order to provide biodiesel dosage in the fuel mixture there were additionally installed flow meter and dispenser (positions 3 and 4 in Fig. 1) into the contour of diesels 2 and 3 [18; 19].
The main values measured in the experiment were specific effective fuel consumption and con-
centration of nitrogen oxides in exhaust gases. Load on diesel engines during the experiments was varied in the range of 25.85% of nominal value.
As a result of researches the following has been established. Fuel mixture containing 5.20% of biodiesel provides 7.7.23.8% decrease of nitrogen oxides concentration in exhaust gases, at that specific fuel consumption increases by 1.5.3.9%. Further research will make it possible to determine the optimum concentration of biodiesel in the fuel mixture for different operational modes of diesel engine operation.
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