First, the geometry model and the calculation mesh of single-cylinder direct injection diesel engine are built, using ESE module of the 3D simulation software AVL FIRE v2014 [1]. Then, by setting appropriate boundary condition, initial condition and calculating step length, and selecting spray, the burning emissions on model and on the basis of adjusting the parameters, a scientific and reasonable simulation platform is built. Emission characteristics of single-cylinder diesel engines in oxygen-enriched, oxygen-enriched + EGR (inlet adding CO 2), and separately using EGR would be studied. It is concluded that EGR synergy oxygen-enriched combustion is beneficial to exhaust treatment and 21% CO 2 + 23% oxygen content is the optimal matching to improve diesel engine exhaust emissions.
Diesel engine is a power plant of the highest efficiency of all the internal combustion engines; it has good power performance, economy and durability, more and more widely used in all kinds of vehicles and power plant. Because of all kinds of advanced technology used in diesel engine, it also gradually changes to the engine of high efficiency and energy saving from the traditional one of heavy smoke and big noise. However, along with the people’s environmental protection consciousness enhancement and increasingly stringent emission regulations [
For compression ignition engine, using AVL FIRE v2014 to simulate mainly include building geometry model of engine according to the structural parameters of combustion chamber, meshing of the combustion chamber geometry model, according to the experiment data and experience set the combustion initial conditions, boundary conditions, etc., selecting the appropriate gas flow model, the combustion model and emission model.
In this paper, regarding single-cylinder diesel engine as the research object, the basic parameters and boundary conditions are shown in
The type of single-cylinder diesel engine’s combustion chamber shape is ω, pit center deviating from the cylinder center slightly, and simplifying it was symmetrical based on the center of the cylinder combustion chamber. To shorten the calculation time, combustion chamber is simplified according to the number of injector nozzle, and only calculates the single spray hole corresponding to the combustion chamber. By ESE module of the FIRE, combustion chamber geometry simulation model is established and it is shown in
Name | Unit | Parameter |
---|---|---|
Cylinder Diameter | mm | 105 |
The Length of Connecting Rod | mm | 200 |
The Piston Stroke | mm | 120 |
Nozzle and Aperture | mm | 7 × 0.216 |
Injection Time | deg | 714 - 734 |
Temperature of the Fuel Injection | K | 330.15 |
The Initial Inlet Temperature | K | 386 |
The Temperature of Cylinder Wall | K | 470 |
Cylinder Head Temperature | K | 570 |
The Piston Surface Temperature | K | 570 |
Compression Ratio | - | 16:1 |
Fuel Injection Quantity per Cycle | kg | 1.7286e−5 |
Engine Speed | r/min | 2000 |
The Turbulence Model | - | K-ZETA-F |
The Nozzle Type | - | Pinhole Type |
The Initial Pressure in Cylinder | MPa | 0.256 |
Due to the existence of a piston reciprocating motion, Multi-dimensional numerical simulation that application of dynamic grid can truly reflect the actual working condition in diesel engine. In order to shorten the calculation time, in this article, dynamic grid from the inlet valve close to the exhaust valve opens is built. Hexahedral grid was used and one seventh of the combustion chamber was divided. In the process of the whole simulation, the size and number of grids on piston top face are fixed, only with the piston movement. The grid number is 1496 and special position’s (top and bottom dead center) grid diagrams are shown in
In this article, the EGR rate was expressed in CO2 in the inlet, the gas flow in cylinder according to the solution of conservation of mass, momentum and energy conservation equations. In order to the equations of closed, need to build a complete simulation model and to select suitable operating parameters. Relevant Models are as follows: Combustion Model is Coherent Flame Model, NOx generation Model chooses the Extend Zeldovich, Soot generation Model selects the Kinetic Model, Spray son Model uses Turbulent dispersion Model, the evaporation Model adopts Dukowicz, broken Model chooses Wave. The relevant operation parameters are as shown in
With the model diesel engine (2000 r/min and full load), the comparison of the pressure’s values of cylinder measured by numerical simulation and experimental testing was shown in
In diesel engine exhaust emission, particulate matter and nitrogen oxides are main pollutants. They are a evaluation index of the good or bad for single-cylinder diesel engine exhaust emissions.
Nitrogen oxides is the main atmospheric pollutants, and it mainly includes NO, NO2, N2O, N2O3, N2O4 and N2O5. NO and NO2 (referred to as NOx), the largest proportion of over 98%. The proportion of NO and NO2 (referred to as NOx) is the largest of all and more than 98%. NO is main and the proportion is about 95% in NOx. Due to the proportion of NO is bigger, we regard NO as main object to study.
The
ponding increase. The conditions of to produce NO in high temperature and oxygen enrichment are conducive to NO. When the oxygen content is 26%, NO significantly rise. If continuing to add content of oxygen, it will produce a lot of NO and this is not conducive to reduce NO in exhaust pipe. The
It shows that when CO2 reaches a certain value, the production of NO will mainly depend on dilution effect of CO2. But when oxygen content is constant, it has no dilution effect. The
Particulate Matter (PM) is another main pollutant in exhaust emissions of diesel engine [
The
To sum up, appropriate CO2 (21%) and O2 (23%) will be useful for single-cylinder diesel engine to reduce pollutants.
This paper, by means of numerical simulation, studied emission performance of single-cylinder diesel engine of oxygen-enriched, oxygen-enriched + EGR (adding CO2 in inlet) and only EGR.
1) The synergy between EGR and oxygen-enriched combustion contributes to reducing diesel exhaust emissions.
2) On the premise of making comprehensive consideration for emissions of Particulate Matter and NOx, we conclude that 21% CO2 + 23% O2 is ideally matched.
Oxygen-enriched combustion can help fuel fully burn, but if O2 is sufficient, temperature of cylinder will rise and it will lead to NOx emissions increase. Just at the moment, by adding CO2 of high specific heat capacity, it can properly reduce NOx. EGR + oxygen-enriched combustion is a new method for diesel engine exhaust after treatment.
The authors acknowledge Shanghai University of Engineering and Science for giving financial supports to this project with No. 15KY0609. This paper is funded by Opening Project of Shanghai Key Laboratory of Multiphase Flow and Heat Transfer in Power Engineering.
Changwei Ding,Weijun Liu, (2016) Numerical Simulation of Emission Characteristics for Single-Cylinder Diesel Engine. Energy and Power Engineering,08,92-98. doi: 10.4236/epe.2016.82008