This paper examines the physical properties of spray development and combustion characteristics using the mixture of gasoline and biodiesel in the compression ignition (GCI) gasoline engines, simulated using the constant volume combustion chamber (CVCC). There are few studies on the spray and combustion properties of ignition delay of gasoline and biodiesel blended by optical research.
Introduction
Background
CO, HC, and NOx emissions from automobiles in Shanghai accounted for 86%, 90%, and 56% of total emissions, respectively. Clean alternative fuels and efficient, low-pollution combustion methods have always been one of the hot spots in internal combustion engines.
Objectives of the study
For the entire automotive industry, clean alternative fuel research has a broad development prospect. Therefore, the study of clean alternative fuels has an extremely important background and far-reaching social and economic impacts for alleviating the energy crisis and reducing air pollution.
Review
GCI engine
- Why choose CI engine?
- Advantages of GCI engine
- Challenges for GCI engine
- Research and current situation of GCI
The last reason is that CI engine performance is closer to an ideal cycle. The focus of the exhaust gas aftertreatment device in the GCI engine is the oxidation of HC and CO, which is much simpler than the control of NOx and PM emissions in a diesel engine, and the required cost is relatively low.
Fuel
- Research and current situation of biodiesel
- Biodiesel – gasoline blend
Statistics show that raw material costs account for 75% of biodiesel production costs. 4. The viscosity of biodiesel is 11 to 17 times higher than that of diesel, and due to its higher chemical structure and molecular weight than diesel, dispersion and combustion problems in the pumping and injector systems of diesel engines are usually more obvious. As diesel fuel consumption in the United States is dominated by agricultural machinery and heavy commercial vehicles, more than 100 highway passenger companies in the United States have become major users of biodiesel.
The main raw materials used for biodiesel production are mainly: rapeseed oil, cottonseed oil, palm oil, castor oil, rice. The experimental results showed that with the increase of the blending ratio of biodiesel, the emission of HC, Co and carbon smoke decreased and that of NOx increased. Considering engine emissions, power and economy, the best mixing ratio is 20% of the biodiesel volume fraction.
When the volume fraction of biodiesel is greater than 20%, its lubricity is basically the same as. As a result, it is difficult to fundamentally solve the problem, which means that the development of a generation of biodiesel in the automotive market continues to be hindered. In recent years, researchers have found it a good method to study fuel spray characteristics using constant volume combustor (CVCC) and optical instruments. The purpose of this study was to understand the injection and combustion characteristics of gasoline-biodiesel (GB) blend under the GCI model using CVCC and provide guidance for further application of GB blend fuel in engines.
A refinement of previous work
At the same time, this study also provides basic data for the simulation research of GB hybrid fuel, it provides guidance for its practical application, which has important guiding significance for the development of GB hybrid fuel under the GCI model.
- CVCC System
- Supply System
- Data acquisition
- Experiment condition
- Definition
The dimensions of the main combustion chamber, sensor data and auxiliary conditions are shown in Table 3.1.1. The design of the diagnostic application is shown in Figure 3.1.4, divided into the following five steps. Also, because the four gases are injected separately into the combustion chamber, the mixing of gas temperature and gas requires a mixing fan to help, so we installed a fan on the side of the CVCC to complete.
The high pressure dynamic pressure sensor is responsible for recording the pressure curve of the heat released during fuel combustion. The charge amplifier then amplifies and converts the pressure sensor signal into a digital signal that is automatically saved to an excel file. Since the spray partially blocks the light passing through it, an image of the movement of the spray can be easily obtained.
A schematic diagram of the optical device and the position of the injector is shown in Figure 3.3.2. In this study, we defined the length of the yellow line shown in the figure as the spray penetration length, i.e. from the nozzle to the farthest end of the shower. The position shown by the green line in the figure represents the size of the angle of the spray cone.
The time point represented by this value was the time of the start of the auto-ignition. We therefore defined the ignition delay as the time interval between the start of the injection and the maximum pressure rise rate achieved during the experiment.
Results of Spray characteristics
Spray development
It can be seen in the picture that the density of the gas environment had a great influence on the development of the spray. Compared to 10 kg/m3, the time for the spray to reach the chamber wall was greatly prolonged at 15 kg/m3. This was due to the increase in ambient gas density, which caused air resistance to spray development, resulting in slower spray development.
Second, the spray area in the 15 kg/m3 condition was much larger than that in the 10 kg/m3 condition, which was also caused by the increase in environmental pressure. Because we have done too many experiments on jet pressure, here we extract 3 groups of examples from the range of 40-90 MPa injection pressure to illustrate the development of spray.
Spray penetration length
As shown, the ambient gas density had a major influence on the penetration length of the spray because the increase in the ambient gas density slowed down the development of the spray. This implies that the increase in ambient gas density caused resistance to the development of the nebula. In addition, as the injection pressure increased, the time it took for the most distal end of the spray to reach the same spray distance became shorter and shorter.
The spray length results showed that as the proportion of biodiesel in the blended fuel increased, the viscosity and surface tension of the blended fuel increased, so it was difficult to rapidly decompose and disperse the blended fuel, resulting in an increase in the size of the fuel. spray drops. The larger the size of the spray droplets, the greater their momentum and the less the resistance to forward movement, which led to an increase in the speed of the spray. Therefore, at the same time after injection, as the mixing ratio of biodiesel increased, the penetration distance of the tip increased.
It is common knowledge that for the same injection duration and the same environmental conditions, the injection pressure is proportional to the fuel volume. Therefore, the injection pressure causes an increase in the penetration length of the spray after injection, which can be considered as a consequence of the increase in fuel mass flow rate and spray torque.
Spray angle
Results of Combustion characteristics
Ignition delay
- Effect of biodiesel blend ratio
- Effect of ambient temperature
- Effect of injection pressure
- Effect of gas density
Cetane number is closely related to the ignition delay of a fuel, which is one of the most critical factors governing the combustion characteristics in compression ignition engines. Improper ignition delay in an engine can cause changes in combustion phases, which can have adverse effects. The experimental results clearly showed that as the proportion of biodiesel in the blended fuel increased, the ignition delay decreased, which is because the high cetane value of biodiesel leads to the increase of the cetane value of the mixture, thus reducing the ignition delay, which proved that the addition of biodiesel helped to improve the autoignition capability.
Taking into account the influence of the ambient temperature on the ignition delay, we found that as the ambient temperature increased, the ignition delay of the three fuels decreased significantly. A higher ambient temperature helped to speed up the reaction rate, leading to our conclusion that a higher temperature helps to reduce the ignition delay. As the injection pressure increases, the ignition delay increases because the higher injection pressure promotes the fragmentation of the fuel droplets, resulting in the formation of larger and smaller droplets, accelerated fuel vaporization, and expansion of the spray zone, resulting in a drop in the temperature of the air-fuel mixture.
Ambient gas density was another parameter that affected the magnitude of the ignition delay. We found that with increasing gas density, all three fuels showed a decrease in ignition delay; This happened because as the gas density increased, the collision energy and collision frequency of gas molecules also increased, and increasing the intensity and frequency of molecular collision increased the rate of chemical reaction. Therefore, higher gas density was shown to significantly reduce the ignition delay over the entire experimental temperature range of 900 to 1000 K and density range of 10 to 15 kg/m3.
Conclusions
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