BI-FUEL DUAL FUEL BIOGAS-DIESEL ENGINE
Le Minh Tien
GATEC
The use offossil fuels has caused severe pollution of the atmosphere. CO2 produced by burning fossil fuels is the main emission of greenhouse gases, responsible atmosphere temperature increases leading to climate change and sea level rise, threatening human life. On the other hand fossil fuels in the Earth is limited. The intense exploitation in recent decades has made this resource energy depleted quickly. The increase in oil prices in recent years have reflected this reality. The ability to find large oil resources can be commercially exploited as in the past is almost hopeless.
Another question is what kinds of energy will be used when depletion of fossil fuels. Nuclear power has long been considered the ultimate but the safety is great problem… only renewable energy sources derived from the sun can maintain human civilization until the solar system disappeared!
In our country, biogas is a abundant source of renewable energy. The research of technology of application of this energy have significant sens in saving fossil fuels and reduce emissions of greenhouse gases into the atmosphere.
In this work we study the technology to convert diesel engines to biogas-diesel dual fuel engine. Original Diesel VIKYNO EV2600 engine was chosen. The study was carried out firstly by simulations of mixture preparation and combustion of biogas in the engine based on software FLUENT. Experimental studies are then conducted on a dynamometer Froude. The experimental results in a number of typical cases allows us to adjust the parameters of the model accordingly. From these results we can proceed to compute the simulations in many different operating cases of engine in practice.
The research results allow us to build up a new industrial product: bi-fuel biogas-diesel dual fuel engine model, compact, renovated from the original diesel VIKYNO EV2600 can be applied in practice. The developped technology can be applied to many different types of engines by computing the simulation program has been established in FLUENT.
The research allow us to draw the following conclusions:
1. Biogas is renewable energy derived from solar energy so its combustion products do not cause an increase of concentration of greenhouse gases in the atmosphere. The presence of CO2 reduces the heating value of biogas fuel, reduce burning velocity but it increases charateristic of antidetonation of the fuel, allowing increased compression ratio of the engine. So in cases of using biogas at production station, we can not need to filter out CO2. This allows us to reduce operating costs for the biogas engine.
2. H2S is most harmful in the biogas. For fueling stationary engines, H2S concentration in biogas can be reach to a maximum of 1000ppm. With this requirement we can just use the cheap adsorbed method instead of using expensive absorption method by chemicals to filter H2S. Adsorbed material can be iron shaving, bentonite soil, laterite…
3. The conversion of traditional diesel engines to run on biogas can be made according to method of spark ignition engine, method of dual-fuel engine or method of bi-fuel dual fuel biogas-diesel engine. Dual fuel engine needs a minimum diesel injection for ignition. In operation, the minimum quantity diesel injection for ignition is only about less than 10% of injection at normal regime. But for preventing of over heat of injection system during operation with biogas, minimum injection should be maintained at between 15% and 20% of diesel injection at normal regime. Bi-fuel dual fuel biogas-diesel engine is in principle the same as dual-fuel engines, but in terms of the structure the engine has two independent speed governors. This option is suitable for cases with limited supplies biogas
4. Bi-fuel dual fuel biogas-diesel engine can use biogas speed regulator fitted outside the engine or compact speed regulator mounted directly on the actuator inside the engine. In the first case, original engine no need much improvement but bulky in drive system. In the second case we need to improve the engine cover and the engine axe but it will be very simple in operation. For both these options, the diesel regulator does not change, the biogas regulator command the butterfly effect in biogas flow.
5. The venturi can create a mixture of fuel characteristics in accordance with the requirements of the engine to dual fuel biogas/diesel. Calculate the flow through the simulated mixing device allows us to identify the basic dimensions of parts with engine sizes. Simulation results show that the equivalent ratio of the mixture decreases as the engine speed increases. When the concentration of CH4 in biogas is lower the rate of decreasing is higher. But in terms of the absolute value, the decreasing of equivalent ratio is very small, does not affect to the engine’s combustion process. For biogas fuel with CH4 concentrations from 60% to 90%, we can see the value f decreases from 1 (n = 1000 rpm) to 0.96 (n = 2400 rpm). In practical use of stationary engines, engines primarily work at normal speed. Thus for full power of theengine at this regime, we need to design of the mixture device so that the value f = 1 is at the rated speed. At the low speed, the mixture becomes a little richer, but does not affect to the combustion
6. We can establish computational model for simulating of combustion in biogas-diesel dual fuel egine based on fluid dynamics software FLUENT with standard k-eturbulence model, parrtial premixed combustion model, pilot injection spark model in form of cylindrical geometry with ignition energy can be approximated by diesel jet energy. Fuel composition and thermodynamic characteristics of the mixture is calculated and stored as PDF file in function oftemperature and pressure that can be accessed during the computing process in order to shorten the calculating time. The engine characteristics of VIKYNO-EV2600 when running biogas in dual fuel options given by simulation are fitted well with experimental results on the Froude dynamometer
7. The dual-fuel engine power may be greater than the power of the engine when running entirely on diesel. At normal speed regime of dual-fuel engines, we can use poor biogas, without filtering CO2, while ensuring the maximum power of the original engine before converting. This is because of quantity of excess air when running on diesel of the engines are so large, we can increase quantity of biogas fuel to increase engine power without any restrictions on equivalent ratio of the mixture.
8. Advance injection timming angle increases as the concentration of CH4 decreases or/and the engine speed increases. When dual fuel engines run at speed of 2000 rpm using biogas containing 70 vol% CH4, the optimal advance injection timming angle is 30 degrees. In the same operating conditions, the maximum temperature and the maximum pressure in the combustion chamber of dual fuel engine increase as the concentration of CH4 in biogas increases, leading to the increase of expansion work and increase of engine power. For rich biogas, the indicating work cycle of the engine decreases with CH4 concentration in biogas fuel. But for poor biogas, the indicating work cycle decreases faster than CH4 decrease rate due to combustion quality is worse when CO2 concentration in the fuel increases. In this case, at the end of the combustion process there is still a significant quantity of unburnt fuel, although the equivalent ratio of the mixture f <1.
9. The results of this research allow us to design details of parts for converting of diesel engine VIKYNO EV2600 into dual fuel compact biogas-diesel engine which is compact in structure, convenient in use. The results of this study can be applied on different types of diesel engines to create new industrial products contributed to the fossil fuel economy and environmental protection..
