In order to investigate the effects ethanol-diesel blends and altitude on the performance and emissions of diesel engine, the comparative experiments were carried out on the bench of turbo-charged diesel engine fueled with pure diesel (as prototype) and ethanol-diesel blends (E10, E15, E20 and E30) under different atmospheric pressures (81 kPa, 90 kPa and 100 kPa). The experimental results indicate that the equivalent brake-specific fuel consumption (BSFC) of ethanol-diesel blends are better than that of diesel under different atmospheric pressures and that the equivalent BSFC gets great improvement with the rise of atmospheric pressure when the atmospheric pressure is lower than 90 kPa. At 81 kPa, both HC and CO emissions rise greatly with the increasing engine speeds and loads and addition of ethanol, while at 90 kPa and 100 kPa their effects on HC and CO emissions are slightest. The changes of atmospheric pressure and mix proportion of ethanol have no obvious effect on NOx emissions. Smoke emissions decrease obviously with the increasing percentage of ethanol in blends, especially atmospheric pressure below 90 kPa.
Recently, diesel engine has received considerable attention because of its high heat efficiency and low emission; however, with the stringent emission standard and limited petroleum reserve, alternative fuels for diesel engine have been used. As a renewable and oxygen-containing biofuel, ethanol is a prospective fuel for vehicle, which can be blended with diesel or be injected into cylinder directly. There are many studies on the application of ethanol on diesel engine, which focus on the three aspects: application techniques of ethanol on diesel engine, fuel properties of ethanol-diesel blends, and effects on the combustion and emission characteristics of ethanol-diesel blends [
Because ethanol is polar molecule and its solubility in diesel is prone to be affected by temperature and water content, high percentage addition of ethanol to diesel is difficult, especially under low temperature (below about 10°C). In order to mix ethanol and diesel, an emulsifier or cosolvent should be added. Many literatures indicated that aromatic hydrocarbon, middle distillate, and wax content of diesel are important factors of its blend with ethanol [
The physical and chemical characteristics of ethanol-diesel blends are very important to its application on diesel engine. The stability, density, viscosity, surface tension, specific heat, heat value, and cetane number of blends have great impact on the injection, atomization, ignition, and combustion properties, as well as cold start, power, fuel consumption, and emission characteristics of engine. Additionally, the poking and leakage of conventional tank, fuel pipe, and sealing part can be rendered. More stringent demands are necessary for the mixture, transportation, storage, and usage of fuel because of low flash point of ethanol-diesel blends [
The cetane number is an important fuel property for diesel engines. It has an influence on engine start ability, emissions, peak cylinder pressure, and combustion noise. According to research carried out by Li et al. [
Without modification, the ethanol-diesel blends decreased the power of diesel engine and increased the brake-specific fuel consumption; however, the performance of prototype can be rehabilitated after adjusting the fuel delivery and injection timing of engine [
Ethanol-diesel blends can reduce the smoke and PM emissions of diesel engine. The higher this reduction is, the higher the percentage of ethanol is in the blends. The reason is that the oxygen content in blends can promote the combination of fuel and oxygen, even in fuel-rich region [
The irregular emissions of diesel engine were also affected by the addition of ethanol. Cheung et al. [
The atmospheric pressure and air density can affect the combustion process of engine, so the power performance, fuel consumption, and emission characteristics of engine will be different when the engine was run at different altitudes. So far, the application researches of ethanol-diesel blends were almost carried out at low altitude. Therefore, in order to investigate the effects of ethanol-diesel blends on the performance and emissions of diesel engine under different atmospheric pressures, the comparative experiments were done between the engine fueled with pure diesel (as prototype) and ethanol-diesel blends at different altitudes [
The test engine was a 3.298 L, direct-injection, turbocharged diesel engine. The relevant characteristic of detailed engine configuration was given in Table
Engine Configuration.
Type | In-line, 4 cylinders |
---|---|
Displacement (L) | 3.298 |
Combustion chamber | |
Induction system | Turbocharged and intercooler |
Compression ratio | 17.5 : 1 |
Rated power (kW/(r | 73/3200 |
Maximum torque (N | 245/2200 |
The emission test devices included an AC electric dynamometer (AVL AFA Drive 250/4–8), an exhaust analyzer (AVL CEB
The different atmospheric pressures were produced by an engine condition system (AVL ACS1300/300), which can automatically controls the atmospheric pressures and inlet gas temperatures. The inlet of turbocharger compressor was connected to the pressure output of engine condition system, and the pressure sensor and temperature sensor were used. When the
A hydraulic vibration emulsification device was developed, which was installed on the high-pressure pump of diesel engine. The ethanol and diesel were delivered to the emulsification device by two fuel delivery systems. The emulsified ethanol/diesel was injected into the cylinder by pump and injector. The emulsification device can provide different proportions of ethanol and diesel without modifying engine and stopping engine. The emulsification device can use the 95% ethanol without any emulsifier and surfactant. The test diesel is 0# diesel [
The low heat value (
Effects of different atmospheric pressure and mix proportion on equivalent BSFC.
2200 r/min 230 N
3200 r/min 190 N
It can be seen that
It can be seen that
The HC emissions of diesel-ethanol blends under three atmospheric pressures were shown in Figures
Comparison of HC emission of different atmospheric pressure and mix proportion at speed 1400 r/min.
Comparison of HC emission of different atmospheric pressure and mix proportion at speed 2200 r/min.
Comparison of HC emission of different atmospheric pressure and mix proportion at speed 3200 r/min.
Because the ethanol has higher latent heat of vaporization, which reduces the gas temperature and promotes the chilling of cylinder wall, the HC emission rises evidently with the increasing content of ethanol at low speed and load of engine. When engine speeds and loads go up, the temperature of gas and combustion chamber wall increases, which accelerates the formation of mixture gas and promotes the combustion of fuel, so the increasing blends of ethanol has litter influence on the HC emissions at higher engine speed and load. Thus, HC emission had slight increase and reached the level of diesel-fueled engine at some engine loads. Due to its higher latent heat of vaporization and lower cetane number, higher proportion of ethanol reduces the gas temperature and retards the ignition delay, which results in the significant rise of HC emissions of E30 at lower speed and load. Additionally, the limited emulsifiable ability of mixture device at higher proportion of ethanol may be another reason. Based on the above analysis, it can be said that HC emissions of ethanol-diesel blends are depended on the engine speed, load, and the mix proportion of ethanol.
The CO emissions of ethanol-diesel blends under three atmospheric pressures were shown in Figures
Comparison of CO emission of different atmospheric pressure and mix proportion at speed 1400 r/min.
Comparison of CO emission of different atmospheric pressure and mix proportion at speed 2200 r/min.
Comparison of CO emission of different atmospheric pressure and mix proportion at speed 3200 r/min.
The addition of ethanol causes the reduction of gas temperature, which restrains the oxidation of CO, so CO emission goes up at low load. With the increase of engine speed and load, the increase of gas temperature, wall temperature, and oxygen content of ethanol promote the oxidation condition of CO, which decreases the negative effect of addition of ethanol. At full load, the excess air ratio is comparatively low, so the increasing proportion of ethanol decreases the CO emission greatly. With the increase of atmospheric pressure, the excess air ratio increases and the effect of ethanol is weakened, so the influence of atmospheric pressure on the CO emission is slight. Based on the above analysis, it can be said that CO emissions of ethanol-diesel blends are depended on the engine speed, load, and the mix proportion of ethanol.
Figures
Comparison of NOx emission of different atmospheric pressure and mix proportion at speed1400 r/min.
Comparison of NOx emission of different atmospheric pressure and mix proportion at speed 2200 r/min.
Comparison of NOx emission of different atmospheric pressure and mix proportion at speed 3200 r/min.
Figures
Comparison of smoke of different atmospheric pressure and mix proportion at speed 1400 r/min.
1400 r/min 140 N
1400 r/min 180 N
Comparison of smoke of different atmospheric pressure and mix proportion at speed 2200 r/min.
2200 r/min 160 N
2200 r/min 230 N
Comparison of smoke of different atmospheric pressure and mix proportion at speed 3200 r/min.
3200 r/min 140 N
3200 r/min 190 N
The oxygen atom is usually connected to carbon atom in oxygenated fuel, and it is difficult to break the bond, which restrains the formation of aromatic hydrocarbon and black carbon, so the oxygen content of ethanol can provide oxygen atom in the fuel-rich region and inhibit the formation of smoke, especially at heavy load. At heavy load, the excess air ratio is low, so the oxygen content of ethanol can show greatly positive effect on the smoke emission. On the other hand, ethanol has lower carbon and sulfur percentage, little aromatic hydrocarbon, and lower surface tension and boiling point, which can promote the spray and combustion characteristics of ethanol-diesel blends and restrain the smoke emission.
The power performance of engine fueled with ethanol-diesel blends can meet the demand of prototype after adjusting the fuel delivery. With increasing atmospheric pressure, the equivalent specific fuel consumption of both mixtures and pure diesel showed the same trend of decrease. When the atmospheric pressure is lower than 90 kPa, the equivalent specific fuel consumption is significantly improved with the rise of atmospheric pressure; and the improvement is weakened when atmospheric pressure is above 90 kPa.
At 81 kPa, the HC emission rises greatly with the decrease of speed and load and the increase of ethanol content, especially at low load. The increasing mix proportion of ethanol has little influence on the HC emission when atmospheric pressure ranges from 90 kPa to 100 kPa.
At 81 kPa, the CO emission rises greatly with the decrease of speed and the increase of ethanol content, especially at low load. At 90 kPa and 100 kPa, the CO emission increases slightly with the increasing mix proportion at low and middle load, while the CO emission is reduced at heavy load.
Atmospheric pressure and mix proportion have no obvious influence on NOx emission. Under most working conditions, NOx emission of ethanol-diesel blends has a slight drop compared to that of diesel.
The smoke emission drops obviously with increasing atmospheric pressure. Furthermore, the higher mix proportion of ethanol results in the lower smoke emission. Atmospheric pressure has significant effect on the smoke emission when it is lower than 90 kPa. The influence is weakened when it is above 90 kPa.
This work was supported by the National Natural Science Foundation of China (Grant no. 50766001).