Effects of butanol–gasoline blends on SI engine performance, fuel consumption, and emission characteristics at partial engine speeds
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The effects of using butanol–gasoline-blended fuels on performance, fuel consumption, and emission characteristics of a four-cylinder spark-ignition engine were experimentally investigated. The butanol-blending fraction was varied from 10 to 50% by volume. The engine speeds were tested at 2250 and 4250 rpm, while the throttle positions were set at 30% and 70%. The engine performance, specific fuel consumption, and emission properties have been carried out and compared. The results show that, at high throttle position, the flame propagation speed of combustion process as using the butanol–gasoline blends decreases as increasing the butanol-blending fraction and this becomes more obvious with the increase of engine speed. The engine brake torque and power are improved, as the butanol-blending fraction is less than 30% at low open throttle position, while those are gradually decayed as increasing throttle opening level. A significant reduction is observed in specific fuel consumption, as the butanol-blending fraction is less than 30% for all the tests. The emissions of CO, HC, and CO2 in the case of using butanol–gasoline blends are much better than those in the case of using pure gasoline. However, NOx emission is worse than that of the pure gasoline for all the test blends.
KeywordsRenewable energy Butanol–gasoline blend Fuel consumption Pollutant emissions Biofuel
Relative air/fuel ratio
Percentage of butanol in the fuel (in volume)
Brake-specific fuel consumption
Crank angle degree
Engine control unit
Electronic fuel injection
Port fuel injection
The greenhouse effect is a big concern in our modern world for the last few decades, as it is significantly influenced by the pollutant emissions generated from the combustion of fossil fuels . Consequently, the automotive industry investigators turn their attention to the alcohol as an alternative fuel in an internal combustion engine for the purposes of reducing the carbon-based fossil fuels and protecting the depletion of oil reserves [2, 3, 4, 5].
To enhance the combustion efficiency and reduce the emissions, the alcohols (e.g., methanol, ethanol, and butanol) have been investigated and widely used as alternative green fuels in spark-ignition (SI) engines [4, 6, 7, 8, 9, 10, 11]. Particularly, methanol can be produced based on many ways, such as coal, natural gas, coke-oven gas, hydrogen, and biomass, while ethanol can be extracted from biomass feedstocks, e.g., corn, sugarcane, barley, and so on [12, 13, 14]. It is well known that biomass processing is the most cost-effective way to produce the methanol and ethanol [15, 16]. Using methanol in SI engines could induce lower reactivity of organic emissions when compared to that of pure gasoline and, therefore, reduces the emission products [17, 18]. However, the methanol combustion induces corrosion on the components, which are made of copper, brass, or aluminum . Since producing methanol is mostly required either coal- or petroleum-based fuels, ethanol has been widely used in biofuel and blending agents as a commercial fuel [20, 21, 22, 23]. Ethanol can be used in different types of internal combustion engines, even without any modification made for the engine. Besides, ethanol– and methanol–gasoline blends burn in a cleaner manner and release fewer emissions compared to those of pure gasoline [21, 24, 25]. In addition, methanol and ethanol have a greater enthalpy of vaporization, larger octane number, faster flame speed, and less stoichiometric air/fuel ratio compared to those of pure gasoline [26, 27, 28].
Compared to methanol and ethanol, butanol has a lower vapor pressure, better blending ability, and greater energy density when used in IC engines [7, 27, 29, 30, 31]. Therefore, these prominent characteristics of butanol would help improve the engine performance and pollutant emissions. Many investigators have examined the performance and emissions of IC engines using butanol. For instance, Feng et al.  studied the performance and pollutant emissions on an SI engine fueled with the butanol–gasoline blend. The experiment was carried out at full load (for an engine speed ranged from 3500 to 9000 rpm) and partial loads (at the engine speed of 6500 rpm and 8500 rpm) for 35% butanol-blending fraction. An additional of 1% H2O was added into the blends to recover the engine performance and control the NOx emission. The results showed that the engine torque, brake-specific energy consumption, CO, and HC emissions are better than those of pure gasoline. The effects of the butanol–gasoline blend on engine performance, fuel economy, and emissions are similar to those occurred at the engine full load and partial loads. Singh et al.  performed a study on butanol–gasoline blends for a powering-duty transportation SI engine. The experiments were conducted at four different engine speeds of 1500, 2500, 3500, and 4500 rpm, while the engine torque was controlled less than 66 Nm. The engine performance, emissions, and combustion characteristics were revealed using different butanol-blending fraction in the blend, e.g., 5, 10, 20, 50, and 75%. The authors concluded that the performance, emissions, and combustion characteristics of the engine using butanol–gasoline blends are similar to those as using gasoline. The performance of an SI engine using gasoline and two butanol-blending fractions (i.e., 20% and 40% butanol by mass) at low and medium engine speeds and loads were reported by Galloni et al. . Results showed that the engine torque and thermal efficiency are slightly decreased as increasing the butanol-blending fraction. The burning rate of lean mixtures increases with increasing butanol-blending fraction and there is no adjustment needed for spark advance as changing the pure gasoline-to-butanol–gasoline blends. Compared to the use of pure gasoline, there is no significant change were made on NOx and CO emissions as using butanol–gasoline blends, while a slight difference was recorded on HC and CO2 emissions. Yang et al.  claimed that butanol is a promising alternative fuel by performing butanol–gasoline blends (e.g., 30% and 35% butanol by volume) without modifying a carburetor SI engine. Results indicated that the energy can be saved by reducing 14% in brake-specific energy consumption and the emissions are significantly reduced compared to pure gasoline. However, the NOx emission is gradually increased as increasing butanol-blending fraction.
Although there are many types of research concerning n-butanol–gasoline blends in SI engines, the relationship between the engine speed, throttle position, and butanol-blending fraction, which affect the performance, fuel consumption, and emissions of the engine, has not been completely investigated at the same time. Besides, the information of comparison between different butanol–gasoline blends and pure gasoline is still limited. Therefore, this study presents the experimental results conducted with different throttle positions and engine speeds as well as butanol-blending fractions. The engine performance in terms of in-cylinder pressure, brake torque, power, and brake-specific fuel consumption has been examined and compared for both butanol–gasoline blends and pure gasoline. The blending ratio applied of n-butanol–gasoline in fuel mixture is covered for the range of 10–50 vol. %. In addition, the emission characteristics of the engine in term of CO, HC, CO2, and NOx have been presented and discussed.
Specifications of the test engine
Number of cylinders/arrangement
Bore (mm) × Stroke (mm)
79.0 × 81.5
80 kW at 6000 rpm
145 Nm at 3400 rpm
Electronic fuel injection
Composition (C, H, O) (% mass)
65, 13.5, 21.5
86, 14, 0
Density (kg/m3) at 20 °C
Boiling point (°C)
Latent heat of vaporization (kJ/kg) at 25 °C
Saturation pressure (kPa) at 38 °C
Low heating value (MJ/kg)
Auto ignition temperature (°C)
Stoichiometric air/fuel ratio
Results and discussion
At a high throttle position (i.e., 70% of WOT) and an engine speed of n = 2250 rpm (Fig. 3c), the peak value of in-cylinder pressure in the case of Bu0 exhibits a larger value compared to that of the other butanol–gasoline blends. The peak value of in-cylinder pressure is decreased gradually, as increasing the butanol-blending fraction. For instance, the reduction of maximum in-cylinder pressure for the case of Bu10, Bu30, and Bu50 is about 11.5, 13, and 17%, respectively, compared to that of Bu0 case. This is because the butanol–gasoline blends have a lower heating value compared to that of pure gasoline (Table 2).
Similar to that occurred in Fig. 3c, at the engine speed of n = 4250 rpm (as shown in Fig. 3d), the peak value of in-cylinder pressure drops as increasing the butanol-blending fraction due to the low heating value of the blends and non-homogeneous of the fuel mixture. This is because lean air/fuel mixtures (Fig. 2) burn more slowly than stoichiometric mixtures leading to lower peak pressures appearance. In this study, the formation of in-cylinder pressure can be used to explain the behavior of laminar flame speed (or flame propagation speed) when using different blends, since the spark-ignition timing is fixed. As shown in Fig. 3c, d, the flame propagation speed of the blend fuels decreases as increasing the butanol-blending fraction. This happens more obvious as increasing the engine speed due to the greater latent heat of vaporization in the blends.
Brake torque and power
As shown in Fig. 4, the brake torque values increase rapidly as increasing the throttle valve opening for all the test cases. For instance, at the butanol-blending fraction of 20%, the brake torque is about 89 and 103 Nm as 30% and 70% of WOT, respectively, at the engine speed of n = 2250 rpm, while it is about 78 and 113 Nm as an open throttle of 30% and 70%, respectively, at the engine speed of n = 4250 rpm. In general, at low throttle position (i.e., 30% of WOT), the brake torque is slightly increased with increasing the percentage of butanol in butanol–gasoline blended and reaches a peak at Bu25. For instance, the increment of brake torque at Bu25 is about 5% and 6% compared to pure gasoline at n = 2250 and 4250 rpm, respectively. When the butanol-blending fraction goes beyond 30%, the brake torque starts to decrease slightly, as the RAFR increases rapidly (Fig. 2). At high throttle position (i.e., 70% of WOT), the brake torque decreases gradually as increasing the butanol–gasoline blend ratio. This is because the pure gasoline exhibits a low value of the latent heat and a high value of the saturation vapor pressure as compared to those of butanol [37, 38, 39, 40, 41]. For instance, as shown in Table 2, the low heating value and saturation vapor pressure of the pure gasoline are 43 and 31.01, respectively, while those of butanol are 33.3 and 2.27, respectively. Therefore, the evaporation time of pure gasoline after injecting is shorter when compared to that of butanol–gasoline blends. A higher percentage of butanol in blends causes a non-homogeneous mixture and might lead to an incomplete combustion; therefore, the brake torque is reduced appropriately.
Specific fuel consumption
Without any modification made for the engine, at high throttle position, the flame speed of the butanol–gasoline blends decreases as increasing the butanol-blending fraction. This becomes more obvious with the increase of the engine speed.
The engine brake torque and engine power are increased, and the specific fuel consumption is decreased when compared to those of pure gasoline under the condition of low throttle position since the butanol fraction less than 30%. At 30% of WOT, when the butanol-blending fraction goes beyond 30%, the brake torque decreases slightly as the RAFR increases rapidly. At 70% of WOT, the brake torque decreases gradually as increasing the butanol–gasoline blend ratio.
As the concentration of butanol in blend increases, for both cases of 30% and 70% of WOT, using butanol–gasoline blends produce significant reductions on CO, HC, and CO2 emissions compared to those of pure gasoline.
NOx emission is increased as increase the butanol-blending fraction and it is significantly higher than that of the pure gasoline. For the same condition of engine speed, the higher the throttle position, the greater the NOx emissions.
This work was funded by The University of Danang-University of Science and Technology under project number T2018-02-05.
Compliance with ethical standards
Conflict of interest
The authors declare that they have no conflict of interest.
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