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Article

Study on Combustion and Emissions of a Spark Ignition Engine with Gasoline Port Injection Plus Acetone–Butanol–Ethanol (ABE) Direct Injection under Different Speeds and Loads

by
Jufang Zhang
1,2,
Xiumin Yu
1,2,
Zezhou Guo
1,2,*,
Yinan Li
1,2,
Jiahua Zhang
1,2 and
Dongjie Liu
1,2
1
State Key Laboratory of Automotive Simulation and Control, Jilin University, Changchun 130022, China
2
College of Automotive Engineering, Jilin University, Changchun 130022, China
*
Author to whom correspondence should be addressed.
Energies 2022, 15(19), 7028; https://doi.org/10.3390/en15197028
Submission received: 25 August 2022 / Revised: 11 September 2022 / Accepted: 19 September 2022 / Published: 24 September 2022
(This article belongs to the Special Issue Advances in Analysis and Application of Biofuels, Alternative fuels and Combustion Technology)
Browse Figures
Versions Notes

Abstract

:

Highlights

What are the main findings?
  • ABE is an excellent alternative fuel for spark ignition engines
  • ABE fuel enables spark ignition engines to have good power performance and emissions performances
What is the implications of the main findings?
  • Gasoline port injection plus ABE direct injection was adopted in this paper
  • In total, an 80% ABE direct injection ratio can obtain excellent power performance at low and medium engine speeds and loads
  • With the further increase in the engine speed and load, pure ABE is optimal to meet power demands
  • A direct injection ratio between 60% and 80% ABE can keep gaseous and particle emissions at low levels
  • ABE plus gasoline combined injection can improve the combustion performance and emission performances effectively

Abstract

ABE can be used as an alternative fuel for engines. This paper studies the combustion and emission performances of an SI engine with GPI plus ABEDI at different engine speeds and loads. The engine operating conditions included speeds of 1000–2600 rpm at the MAP = 50 kPa and loads of MAP = 30–70 kPa at a speed of 1800 rpm. The ABEDIr contained 0%, 20%, 40%, 60%, 80%, and 100%. At speeds = 1000–1800 or 2200–2600 rpm, the testing results showed the ABEDIr corresponding to the maximum IMEP at 80% or 100%. When the ABEDIr = 60%, HC and NOx emissions were the lowest at speeds of 1000–2600 rpm. Meanwhile, NPN and APN both decreased with the increasing of ABEDIr. As the MAP increased, CA0-90 decreased. At different loads, ABE-added fuels had lower HC and NOx emissions and higher IMEP values than pure gasoline. PN was lower than 4 × 104 n/cm3 when the ABEDIr was over 80%. Overall, 80% ABEDIr is a great choice for engine performance at the test range of loads and speeds, and pure ABE fuel is better if the power performance is the main requirement at high speeds and loads.

Graphical Abstract

1. Introduction

With the exhaustion of fossil energy and the aggravation of air pollution, seeking renewable alternative fuels to alleviate the energy crisis has become a hot topic in the field of internal combustion engines. Researchers around the world are committed to finding clean and renewable alternative fuels to replace fossil fuels [1,2,3,4,5,6]. They have been exploring ways to reduce emissions of exhaust pollutants [7,8,9]. At present, alternative fuels for spark ignition (SI) engines can be distinguished into two types: gaseous fuels (e.g., hydrogen and natural gas) and liquid fuels (e.g., methanol, ethanol, and butanol) [10,11,12,13,14,15]. However, due to the high difficulty of storage and transportation, gaseous alternative fuels are not superior to liquid alternative fuels. Generally, through fermentation, separation, and purification process, the liquid alternative fuels are made of sugar-containing crops and agricultural wastes containing starch and cellulose [16,17,18,19,20]. As important members of bio-fuels, alcohols, especially methanol, ethanol, and butanol, have attracted great attention from scholars worldwide [21]. However, methanol is limited because of its high toxicity, and high requirements for engine lubricating oil and anti-corrosive rubber [22]. Fermented corn, sugar cane, and agricultural residues are excellent feedstocks for bioethanol production [23,24,25,26]. Compared with gasoline, the high octane number and latent heat of vaporization (LHOV) of ethanol contribute to the improvement of the anti-knock and volumetric efficiency in the engine [27]. In addition, ethanol has a higher laminar flame speed (LFS) and lower adiabatic flame temperature, which can improve engine thermal efficiency and reduce gaseous emissions [28]. For biobutanol, the raw materials and the manufacturing equipment are similar to ethanol, in which the production cost is lower [29]. Meanwhile, butanol has better properties than ethanol, such as less causticity to aluminum parts, more resistance to water pollution during long-term storage, and higher energy density [30,31,32,33]. Importantly, butanol can be directly applied to the engine without much modification to the engine structure [34]. Considering the above factors, butanol is more advantageous as a renewable alternative fuel for the spark ignition (SI) engine.
Separation and purification from acetone–butanol–ethanol (ABE) stock solution is the most common method for producing biobutanol, also known as ABE fermentation. This method is costly and inefficient, leading to the lack of widespread application of butanol. ABE is a common raw material for the production of butanol, and the most common ratio of acetone, butanol, and ethanol is 3:6:1, with a high content of butanol. If ABE can be directly applied to automobile engines and retain the advantages of alcohol fuel, it will be a good alternative fuel. Therefore, the research on ABE has also aroused the interest of many scholars. There are several different opinions and methods on how to apply ABE to the engine, e.g., ABE–diesel blends and ABE–gasoline premixed fuel.
For ABE–diesel blends, Wu [35] studied the combustion characteristics of ABE/diesel premixed fuels with ABE ratios of 0%, 20%, 50%, and 80%, respectively, in a constant volume combustion bomb. The results showed that ABE of 50% had a shorter ignition delay period, shorter combustion duration, and lower soot emissions. Zhou et al. [36] studied the combustion characteristics of ABE of 20% diesel and 80% fuel in a constant volume combustion bomb in a conventional combustion mode and low-temperature combustion mode. The results showed that an ABE of 20 had better combustion efficiency than pure diesel under low temperature and low oxygen conditions. Chang et al. [37] tested the performance of the biodiesel–diesel–ABE blends and showed that adding ABE to the biodiesel–diesel blends effectively increased the effective thermal efficiency and reduced the particle and polycyclic aromatic hydrocarbon (PAH) emissions. The combustion and emission performances of compression ignition (CI) engines can be improved by adding ABE, indicating that ABE is an excellent clean fuel for CI engines.
There have also been some studies on the application of ABE in SI engines. The general studies can be divided into pure ABE and ABE–gasoline premixed fuel. For pure ABE, Nithyanandan et al. [38] studied the performance of applying A:B:E = 3:6:1, 6:3:1, and 5:14:1 volume ratios in a single-cylinder port fuel injection (PFI) engine. They found that the peak cylinder pressure of ABE was slightly higher than that of gasoline. They also found that ABE (6:3:1) had a higher brake-specific fuel consumption (BSFC), higher brake thermal efficiency (BTE), and lower hydrocarbon (HC) emissions than pure gasoline. Zhang et al. [39] tested the LFS of different equivalent ratios of acetone, n-butanol, ethanol, and their mixtures in constant volume combustion bombs. The results showed that A:B:E = 1:6:3 has the fastest LFS, followed by A:B:E = 3:6:1 and A:B:E = 6:3:1. For ABE/gasoline blends, Li et al. [40] tested ABE30, ABE85, ABE29.5W0.5, and ABE29W1 on a single-cylinder engine. They found that ABE29W1 had a higher engine torque and lower carbon monoxide (CO), HC, and nitrogen (NOx) emissions compared to gasoline. They [41] also studied fuels with different ABE ratios, A:B:E, ratios and water contents. The results showed that ABE (3:6:1) of 30% had higher BTE and lower CO, HC, and NOx emissions. Nithyanandan et al. [42] tested gasoline/ABE mixtures at ABE (3:6:1) ratios of 0%, 20%, and 40%. The results showed that the in-cylinder maximum pressure of ABE of 20% was higher than that of gasoline, but the CO and HC emissions were relatively increased. Based on the above studies, it can be found that the use of ABE in SI engines can effectively improve combustion and emission performances. However, different engine operating conditions correspond to different optimal ABE/gasoline mixture ratios. It is not the best method for using fixed ABE/gasoline ratio fuels in actual vehicles. Combined injection technology can solve this problem. The combined injection system contains a port injection system and an in-cylinder direct injection system, which could achieve different ABE/gasoline ratios by flexible injection parameters. Therefore, it is innovative and meaningful to combine ABE/gasoline dual-fuel and combined injection technology to explore the effect of ABE on improving engine combustion and emission characteristics under different engine operating conditions and ABE additional ratios.
It is worth mentioning that we have done some experimental studies on the application of ABE fuel in the combined injection engine. In the previous studies [43,44,45], we conducted a comparative study on two kinds of ABE/gasoline combined injection modes and obtained some results on optimal injection strategies. By comparing the combustion characteristics, gas emissions, and particle emissions of the two injection modes under different direct injection pressure, direct injection time, excess air ratio (λ), and ignition timing, the results showed that gasoline port injection (GPI) + ABE direct injection (ABEDI) was the best injection approach for ABE, compared to GDI + ABEPI. Meanwhile, the GPI + ABEDI mode adopting an ABE direct injection ratio (ABEDIr) of 80% combined with a DIT of 300 °CA BTDC at λ of 1.0 can be regarded as the best way. However, as important practical operating conditions, changes in engine speed and load have not been thoroughly studied for their effects on gasoline/ABE engine performance. While engine speed and load are very important parameters that vary with the driver’s demand during engine operation, it is necessary to further clarify whether ABEDI has the potential to improve combustion and emissions at different speeds and loads, as well as to determine the optimal ABE/gasoline dual-injection strategy. Based on the above, the combustion and emission characteristics and the optimal injection strategy of GPI + ABEDI engine under different speeds and loads are investigated further the by engine test bench in this paper.

2. Experimental Setup and Procedure

2.1. Engine and Test Equipment

This experiment was based on the engine test bench. The specific engine parameters are shown in Table 1. The test engine is a four-cylinder combined injection SI engine. As shown in Figure 1, the engine includes two fuel supply systems, the port injection system and the in-cylinder direct injection system, which can realize the independent control of the port fuel injection and in-cylinder direct inject pulse width. In this test, the port injection system was used to inject gasoline into the manifold, while the direct injection system was used to inject ABE into the cylinder. Figure 2 is a structure diagram of the engine test bench. The engine power performance, combustion, and emission data were obtained with the experimental instrument.
The parameters of the measuring instrument used in the test are shown in Table 2. CW160 eddy current dynamometer was used to control and measure the engine speed and torque. An Ono Sokki DF-2420 fuel consumption meter was used to obtain gasoline consumption data. An AVL-GU13Z-24 spark plug pressure sensor was installed in the second cylinder to obtain in-cylinder pressure. Crankshaft angle was measured by a Kistler 2614B crankshaft angle encoder. The Dewesoft combustion analyzer calculated the combustion data by collecting 200 cycles. An ETAS Lambda Meter 4 broadband oxygen sensor was installed in the exhaust pipe to monitor the oxygen content in the exhaust gas and calculated the λ value in real-time. For gaseous emissions, AVL-Ditest Gas 1000 was used to test HC, CO, CO2, NOx, and O2 emissions. DMS500 was used to measure the particle number (PN), accumulation particle number (APN), and nucleation particle number (NPN). All the engine sensors and actuators were controlled by the dSPACE rapid prototyping system.

2.2. Experiment Fuels and Properties

In this study, 95-octane ethanol-free gasoline was used as the port injection fuel. For in-cylinder direct injection fuel, ABE with acetone:butanol:ethanol = 3:6:1 was chosen, which is the most common ABE fermentation product. Table 3 lists the physicochemical properties of acetone, butanol, ethanol, ABE (3:6:1), and gasoline.

2.3. Experimental Procedure

The experiment was divided into two parts. The specific experimental scheme is shown in Table 4. First, we tested the combustion and emission performances at different ABEDIr (0%, 20%, 40%, 60%, 80%, and 100%) when the engine speed = 1000–2600 rpm (in increments of 400) and the intake manifold absolute pressure (MAP) = 50 kPa. Then we changed the MAP between 30, 40, 50, 60, and 70 kPa at the fixed speed of 1800 rpm, and tested combustion and emission performances at different ABEDIr (0%, 20%, 40%, 60%, 80%, and 100%). During the experimental process, when adjusting the ABEDIr at a fixed speed and load, we ensured that the air intake amount was always constant under different ABEDIr. The ABEDIr in this paper can be understood as the gas consumption ratio, assuming that the air amount was Q and the mass flow rate of pure gasoline port injection was M at λ = 1. When a certain ABEDIr was needed, the port injection pulse width should be adjusted first, so that the port gasoline mass flow rate could reach the target value of Massgasoline in Formula (1). Then, the λ was brought back to 1 by adjusting the ABE pulse width. At different engine speeds and loads, each ABEDIr could be achieved by using the same method.
M a s s g a s o l i n e = M ∗ ( 1 − A B E D I r )
where Massgasoline represents the mass of gasoline under the combined injection mode and M is the mass of pure gasoline port injection without ABE direct injection.
It should be noted that considering that the lower heating value (LHV) and stoichiometric air–fuel ratio of gasoline and ABE are different, the λ and the total energy of ABE/gasoline dual-fuel cannot be consistent with pure gasoline at different ABEDIr even with the same intake air volume. We fixed λ and the total energy changed inevitably. However, the calculation results showed that the total energy difference was no more than 1% between ABE/gasoline dual-fuel and pure gasoline, which can be ignored. The definition and total energy change in the different ABEDIr fuels in the experiment are shown in Table 5.
In total, using the combined injection engine test bench, this paper explores the potential of using ABE as an alternative fuel in common operating conditions of gasoline engines at five speeds and five MEPs in the experiments. The maximum ABE ratio that the gasoline engine could blend was analyzed. The engine power performance, mixture combustion state, and emissions performances after blending with ABE were carefully studied. The details of the research are shown below.

3. Results and Discussion

3.1. Combustion Characteristics

3.1.1. CA0-90

Figure 3 shows the change in the CA0-90 with the change in ABEDIr at different engine speeds when MAP = 50 kPa. With the increase in ABEDIr, CA0-90 first decreased and then increased. Due to the high LFS of n-butanol and ethanol, the combustion speed of the in-cylinder mixture increased with increasing ABEDIr, so the CA0-90 decreased first. The cooling effect of ABE on the in-cylinder mixture led to a lower temperature, which prolonged the ignition delay period. Due to the low LHV of ABE, the increase in ABE was about 1.3 times the amount of gasoline reduction, and the increase in the fuel amount in the cylinder also lengthened the combustion process. Therefore, a large percentage of ABEDIr increased the CA0-90.
It can also be seen that, with the increase in engine speed, CA0-90 first increased and then decreased when ABEDIr = 0–60%. This is because the airflow velocity increased with the increasing engine speed, which accelerated the heat transfer of the initial flame core, increasing the ignition delay period. The increase in engine speed also made the crankshaft angle occupied by the combustion process longer, so the CA0-90 increased, while, with the continuous increase in engine speed, the increase in airflow motion intensity improved the flame propagation speed. The heat transfer loss decreased, making the in-cylinder temperature increase at the end of the compression stroke. The above factors were conducive to stable ignition and faster flame propagation, so the CA0-90 would decrease at high engine speeds.
When ABEDIr = 80–100%, CA0-90 decreased continuously with the increase in engine speed, especially from 1000 to 1400 rpm. At high ABEDIr, the high viscosity and the high LHOV of ABE can cause poor evaporation, resulting in uneven air–ABE mixing under the weak in-cylinder airflow intensity. With the increase in engine speed, the enhancement of airflow motion intensity was beneficial to the evaporation and mixing of fuel, and the mixture was more uniform. Meanwhile, the increase in engine speed promoted the flame propagation speed and shortened the combustion duration. Although increasing the engine speed increased the heat transfer from the initial flame core, the abundance of OH radicals provided by high ABEDIr fuel or pure ABE increased the reactivity and flame propagation speed, resulting in a sustained decrease in the CA0-90 with engine speed. If the problems of poor evaporation and mixing of high ABEDI fuel are solved, the promoting effect of ABE on combustion would become prominent deeply.
Figure 4 shows the variation in the CA0-90 with ABEDIr at different loads at an engine speed of 1800 rpm. CA0-90 continued to decrease as MAP increased. This is mainly because increasing MAP meant increasing the throttle opening, and the increased intake pressure reduced the residual exhaust gas in the cylinder. The reduction of the residual exhaust gas coefficient increased the ignition stability and flame propagation speed. On the other hand, the increase in MAP made the in-cylinder thermal atmosphere better, and the rise in the in-cylinder temperature at the end of the compression stroke made it easier to form a stable flame core, promoting the rapid propagation of the flame. Combining the above factors, CA0-90 continued to decrease with the increase in MAP.
Furthermore, CA0-90 at each MAP first decreased and then increased with the increase in ABEDIr. This is because the oxygen-containing components in ABE improved the reactivity and increased the flame speed, so the CA0-90 would first decrease with the increase in ABEDIr. However, the effect of the ABE evaporation and mixing became worse with the increase in ABEDIr, due to the high LHOV and a large amount of ABE being injected. Inhomogeneous mixtures would delay the combustion process, so the CA0-90 increased at high ABEDIr.
Notably, when MAP = 30–70 kPa, the CA0-90 reached the lowest values at ABEDIr of 40%, 60%, 60%, 80%, and 80%. Especially when MAP = 30–60 kPa, CA0-90 of pure ABE was much higher than the minimum CA0-90 at the same MAP. However, the results can still show that with increasing MAP, the optimal ABEDIr increased, and the engine was more tolerant of high ABEDIr fuels. This is due to the high LHOV and low saturated vapor of butanol; a smaller ABEDIr could ensure complete evaporation of ABE in a poor in-cylinder thermal environment. When the MAP increased, the in-cylinder thermal environment became better, which was beneficial to complete evaporation and mixing of high ABEDIr fuel. At this time, the advantage of the high LFS in promoting combustion would become more obvious, so the ABEDIr corresponding to the minimum CA0-90 increased, making the high ABEDIr fuel competitive.

3.1.2. IMEP

Figure 5 shows the change in IMEP with ABEDIr at different engine speeds when MAP = 50 kPa. It can be seen that at the speed of 1000–1800 rpm, IMEP first increased and then decreased with the increase in ABEDIr, reaching the maximum value at 80% ABEDIr. As mentioned earlier, with the increase in ABEDIr, the LFS and oxygen content of ABE were higher than gasoline, which made the exothermic process more concentrated and the in-cylinder combustion more complete. For fuels with high ABEDIr, the IMEP was low due to the incomplete evaporation mixing caused by the large injection amount and high LHOV. Therefore, IMEP first increased and then decreased with the increase in ABEDIr.
At the speeds of 2200 and 2600 rpm, IMEP continued to increase with the increase in ABEDIr. This is because the turbulence intensity of airflow is strong at high engine speeds, which can improve the evaporation and mixing of gasoline and high-viscosity ABE. At high engine speed, the in-cylinder heat transfer loss was reduced and the temperature at the end of the compression stroke rose, which was beneficial to improve ABE evaporation and reduce ignition delay. After solving the problem of poor evaporation and mixing of high ABEDIr, the promoting effect of the high LFS and the OH radical on reactivity would become obvious. Therefore, IMEP increased with the increase in ABEDIr at 2200 and 2600 rpm. High ABEDIr was more suitable at high engine speed conditions.
In addition, IMEP showed an increasing trend with engine speed. This is because, as the engine speed increased, the increased airflow movement intensity improved fuel atomization, evaporation, and mixing. Meanwhile, the heat transfer losses decreased with the increasing engine speed, leading to an increase in in-cylinder temperature at the end of compression. All these factors contributed to more homogeneous mixing and a more complete combustion process. The maximum IMEP was 6.1%, 6.2%, 5.2%, 6.7%, and 8.4% higher than pure gasoline at 1000–2600 rpm, respectively, which indicated that adding ABE had a more obvious effect on promotion combustion at high engine speeds. Taken together, 80% ABEDIr fuel and pure ABE were competitive at high engine speeds.
Figure 6 shows the variation in IMEP with ABEDIr at different MAP at 1800 rpm. When MAP = 30, 40, and 50 kPa, IMEP first increased and then decreased with ABEDIr, reaching the maximum value at 60%, 80%, and 80% ABEDIr, respectively. As mentioned above, increasing ABEDIr would increase the oxygen content and flame speed, resulting in more complete combustion. With the further increase in ABEDIr, the in-cylinder thermal atmosphere was poor at small and medium loads, which cannot guarantee complete evaporation of high ABEDIr fuel to form a homogeneous mixture. The high LHOV of ABE can further weaken the thermal atmosphere, finally hindering the formation of the initial fire core and the stable propagation of flame. Under low and medium loads, only adopting appropriate ABEDIr fuel to ensure complete evaporation can show the promoting effect of ABE on combustion.
At the high load conditions of MAP = 60 and 70 kPa, IMEP continued to increase with the increase in ABEDIr, and pure ABE owned the highest IMEP. ABE has a better evaporation condition, and the advantages of the chemical properties of ABE were highlighted at high loads. When MAP = 30–70 kPa, the maximum IMEP was 6%, 4.5%, 5.1%, 6%, and 6% higher than pure gasoline, respectively. Since the total energy of ABE/gasoline dual-fuel or pure ABE was less than 1% higher than that of pure gasoline, the addition of ABE did significantly improve the engine power performance under different loads. ABEDIr of 80% and 100% can be regarded as the best. ABEDIr should be increased with the increase in MAP for better engine power performance.

3.2. Gaseous Emissions

3.2.1. NOx Emissions

Figure 7 shows the variation in NOx emissions with engine speeds at ABEDIr of 0–100% when MAP = 50 kPa. Under different ABEDI ratios, NOx emissions first decreased and then increased with the engine speed, and reached a lower level at 1800 rpm. With the increase in engine speed, the residence time of the burnt gas under high temperatures decreased, suppressing the generation of NOx. When the engine speed continued to increase, IMEP presented an upward trend, and thorough combustion promoted the increase in the in-cylinder temperature. According to the NO formation mechanism, the N2 decomposition requires large activation energy which makes a high-temperature condition the core factor determining the formation of NO [50,51]. The promotion effect of high temperatures on NO production is greater than the effect of short residence time. Therefore, NOx emissions would rise at high speed.
At different engine speeds, NOx emissions first decreased and then increased with the increase in ABEDI, reaching the lowest value at 60% ABEDIr. The adiabatic flame temperature of ABE is lower than gasoline due to the higher LHOV, and the higher specific heat capacity of combustion products. Lower in-cylinder temperature led to a decrease in NOx emissions with the increase in ABEDIr. When ABEDIr increased further, combined with Figure 3 and Figure 5, IMEP continued to increase and CA0-90 continued to decrease, indicating that the heat release process was rapid and concentrated, which increased the in-cylinder temperature. Meanwhile, the high oxygen content of ABE also promoted the formation of NOx emissions. In general, NOx emissions of ABE/gasoline dual-fuel were lower than pure gasoline, and the medium engine speed was conducive to reducing NOx emissions.
Figure 8 shows the variation in NOx emissions with ABEDIr at different MAPs when the engine speed is 1800 rpm. It can be seen that NOx emissions continued to increase with the increasing MAP. This is because the high in-cylinder temperature and oxygen-rich conditions promoted the generation of NOx, while the increase in MAP resulted in large fuel injection and a high combustion temperature, leading to a significant increase in NOx emissions.
With the increase in ABEDIr, NOx emissions first decreased and then increased, reaching the lowest value at 60% or 80% ABEDIr. When MAP = 30–70 kPa, the lowest NOx emissions were 34.4%, 35%, 23.4%, 19.6%, and 18.7% lower than those of pure gasoline. The effect of adding ABE on reducing NOx emissions became weaker as MAP increased. The combustion temperature rose substantially with the increase in MAP, and the heat absorption by ABE evaporation and the lower adiabatic flame of ABE had limited effects on the reduction of combustion temperature, resulting in a decrease in a reduced-NOx emissions reduction effect. NOx emissions of ABE/gasoline dual-fuel or pure ABE are lower than those of pure gasoline, which means that the NOx emissions would not deteriorate after adding ABE at different engine speeds.

3.2.2. HC Emissions

Figure 9 shows the variation in HC emissions with engine speed at different ABEDIr when MAP = 50 kPa. HC emissions first decreased and then increased with the increase in ABEDIr at different engine speeds, and reached the lowest value at 60% ABEDIr. This is because, with the increase in ABEDIr, the concentration of oxygen-containing radicals increases in the chemical reaction, which improves the local anoxic combustion and accelerates HC oxidation [52]. When the ABEDIr continued to increase, the increasing amount of ABE was greater than the decrease in gasoline due to the low stoichiometric air–fuel ratio of ABE. Therefore, a substantial increase in the total fuel amount would increase HC emissions. Furthermore, the high LHOV and high viscosity of ABE worsened the evaporation process with the increase in ABEDIr. An increase in the amount of ABE resulted in more droplets hitting the combustion chamber walls. Therefore, HC emissions showed an increasing trend at 80% and 100% ABEDIr.
At different ABEDIr, HC emissions continued to decrease with the increasing engine speed. The increase in engine speed enhanced the in-cylinder airflow movement, and the high turbulence made the air and fuel mix evenly, avoiding HC emissions caused by incomplete combustion. In addition, the high-speed airflow would strengthen the evaporation of the wall oil film and reduce the HC emissions generated by the diffusion combustion of the fuel film at low temperature [53]. The increase in engine speed would also increase the flame propagation speed, making the flame more likely to reach the wall surface, which would strengthen the oxidation of the quenching layer. Meanwhile, with the increase in engine speed, the exhaust temperature increased greatly, which was beneficial to the late oxidation of HC emissions. Therefore, HC emissions continued to decrease with the increase in engine speed.
HC emissions of ABE-containing fuel were lower than that of pure gasoline at each test engine speed, and the increase in speed was beneficial to the reduction of HC emissions.
Figure 10 shows the variation in HC emissions with ABEDIr under different loads at the engine speed of 1800 rpm. Under the condition of pure gasoline or 20% ABEDIr, HC emissions first increased and then decreased with the increase in MAP. When the ABEDIr continued to increase, HC emissions continued to decrease with the increase in MAP. When the main component in the cylinder was a mixture of 0% or 20% ABEDIr, the increase in MAP resulted in a significant increase in the amount of gasoline port injection. Low-pressure port injection of gasoline would lead to the inhomogeneous mixture and the formation of local fuel enrichment areas, eventually leading to high HC emissions. After further increasing the MAP, the improvement of the in-cylinder thermal atmosphere and the combustion temperature were conducive to better evaporation of fuel and later oxidation of HC. When the ABEDIr was 40–100%, the in-cylinder main component was ABE, and the fuel-bound oxygen could better improve the combustion and oxidize HC. Even though increasing the MAP would lead to an increase in the fuel injection amount, the oxidation effect on HC by ABE addition could offset the worsening effect of HC emissions due to the increase in the fuel injection amount. With the increase in MAP, the in-cylinder combustion temperature and thermal atmosphere were improved, which promoted fuel evaporation and reduced the local fuel enrichment area. In addition, the temperature of the piston top and cylinder wall would increase with the increase in MAP, and the thickness of the wall quenching layer would decrease, which is conducive to the flame spreading throughout the combustion chamber. Meanwhile, with the increase in the MAP, the coefficient of in-cylinder residual exhaust gas would decrease, so the probabilities of misfiring and quenching were reduced. The increase in MAP also increased the exhaust temperature, which could strengthen the later oxidation of HC emissions.
Therefore, HC emissions decreased with the increase in MAP when ABEDIr was 40–100%. At different loads, HC emissions first decreased and then increased with the increase in ABEDIr, which was consistent with the phenomenon and reason at different engine speeds. On the whole, HC emissions of ABE-containing fuel at different loads were lower than pure gasoline, which means that adding ABE can effectively decrease HC emissions.

3.2.3. CO Emissions

Figure 11 shows the variation in CO emissions with engine speed at different ABEDI ratios when MAP = 50 kPa. With ABEDIr of 0–60%, CO emissions first decreased and then increased with the increase in engine speed, and reached the lowest value at the speed of 1400 rpm. With the increase in engine speed, the uniformity of the mixture was improved, and the reduction in the local fuel enrichment area hindered the generation of CO emissions. However, with the further increase in the engine speed, the later oxidation time of CO is shortened. Meanwhile, when the ABEDIr was relatively low (0–60%), the oxygen content in the cylinder was insufficient under stoichiometric conditions and the effect of OH radical on CO oxidation was limited. Therefore, the CO emissions showed an upward trend when the engine speed was higher than 1400 rpm. CO emissions could not change much at ABEDIr = 80%.
Differently, at 100% ABEDIr, CO emissions decreased continuously with the increase in engine speed. After increasing the engine speed, the evaporation of pure ABE caused by high viscosity and LHOV were improved, reducing the possibility of CO generation from local anoxic combustion. Combined with Figure 5, IMEP increased with the increase in engine speed, indicating that the combustion temperature was higher at high speed and the OH radicals carried by ABE met the requirements for CO; thus, CO emissions continued to decline. Although the later oxidation time of CO was shortened, due to the large amount of OH radical at pure ABE condition, the increase in the in-cylinder temperature with engine speed became the main factor to reduce CO emissions.
In general, with the increase in ABEDIr, CO emissions first increased and then decreased. The high LHOV of ABE would reduce the in-cylinder temperature, which is not conducive to the oxidation of CO emissions. However, after a large amount of ABE was added, the high oxygen content of ABE played a major role in the oxidation process of CO emissions, resulting in a reduction in CO emissions. High ABEDIr or pure ABE fuels do not worsen CO emissions with changes in engine speed. While using medium ratio ABE fuels, it should be noted that CO emissions worsen at high engine speeds.
Figure 12 shows the variation in CO emissions with ABEDIr at different loads when the engine speed is 1800 rpm. With the increase in MAP, CO emissions continued to decrease, especially from low MAP to medium MAP. At the low MAP, the low combustion temperature and the large amount of in-cylinder residual exhaust gas hindered the oxidation of CO, while the combustion temperature and exhaust temperature rose with the increase in MAP, causing CO to be fully oxidized. With the increase in ABEDIr, CO emissions first increased and then decreased. This is because the high LHOV of ABE would reduce the in-cylinder temperature with increasing ABEDIr, which is not conducive to the oxidation of CO emissions. However, with the further increase in ABEDIr, the oxygen-containing groups carried by ABE can improve the combustion in the anoxic area and enhance the later oxidation of CO, thereby reducing CO emissions.
On the whole, CO emissions can be equal to or lower than pure gasoline only by using 80% ABEDIr fuel or pure ABE at different engine speeds.

3.3. Particle Emissions

In this paper, the NPN denotes the particle number of nucleation mode (5–50 nm diameter), APN denotes the particle number of accumulation mode (50–1000 nm diameter), and TPN denotes the total particle number.
Figure 13 shows the variation in particle number with engine speed under different ABEDIr when MAP = 50 kPa. It can be seen that with the increase in ABEDIr, the particle number showed a downward trend. Meanwhile, when the ABEDIr reached 80%, the TPN at all engine speeds were lower than 1.5 × 104 n/cm3. With the increase in ABEDIr, the oxygen-containing groups in the mixture would increase, which can inhibit the growth of PAHs, and the reduction of gasoline injection amount would also reduce the content of PAHs carried by gasoline. Both factors acted simultaneously to reduce the formation of particle precursors. In addition, due to the low combustion temperature of ABE, when ABEDIr was higher, the number of particle precursors produced by the pyrolysis of fuel at high temperatures was also reduced.
At different ABEDI ratios, NPN and APN both first increased and then decreased with the increase in engine speed, and reached the maximum value at 1800 rpm. This is due to poor combustion stability at low engine speeds. Although the incomplete vaporization and mixing of ABE at low speeds can lead to a local enrichment area of fuel, the temperature in the cylinder was low, which did not meet the high-temperature conditions required for particle formation. Incomplete combustion fuel was discharged from the cylinder in the form of HC, which can be verified by the highest HC emissions at 1000 rpm. When the speed increased, the IMEP increased greatly, and the rising combustion temperature made the cylinder temperature high. Then, the soot precursors were produced by fuel pyrolysis in the local concentration area, and particle emissions were formed by nucleation and surface growth from soot precursors. Thus, PN increased when the engine speed changed from 1000 to 1800 rpm. As the engine speed further increased, the in-cylinder temperature remained at a high level, and the increase in airflow motion intensity made the mixture more homogeneous. The local gaseous and liquid enrichment areas generated by poor evaporation and mixing were greatly reduced, and the formation of soot precursors by fuel pyrolysis was alleviated. In addition, the airflow with high-velocity flow over the wall can promote the evaporation of the wall oil film, inhibit the diffusion and combustion of the oil film, and reduce the formation of aggregated particles. Therefore, the particle numbers tended to drop at higher engine speeds.
It is worth noting that when ABEDIr was 0%, 20%, and 40%, the particle number (PN) of high engine speed (2200 and 2600 rpm) was higher than that of 1000 rpm. When ABEDIr was 60%, 80%, and 100%, the particle numbers of high speed were lower than low speed or remained unchanged. This is because when the in-cylinder fuel was dominated by ABE, the strong airflow movement at high speed had better evaporation and atomization of ABE. Under this premise, the effect of oxygen-containing groups on particle oxidation can be highlighted. Even if the high in-cylinder temperature at high engine speed intensified fuel pyrolysis tendency, the oxygen-containing groups played a dominant role in reducing particulate matter after ensuring excellent evaporation and mixing of ABE.
While Figure 13 shows that the particle numbers are higher at 0% and 20% ABEDIr, Figure 14 shows the particle size distribution characteristics at different engine speeds when the ABEDIr = 0% and 20%. When the ABEDIr was 0%, the particles showed a unimodal distribution at the speeds of 1000 and 1400 rpm, with a peak size of 13.3 nm. When the engine speed increased to 1800 rpm, the particle size distribution became bimodal, but the peak value of the accumulation particle was low, and the peak particle size of the nucleation was 15.4 nm. When the engine speed continued to increase to 2200 and 2600 rpm, the particle size distribution was unimodal again, and the peak particle size was 17.8 nm. This is due to the increase in in-cylinder combustion temperature when the engine speed ranges from 1000 to 1800 rpm. Pyrolysis of the fuel in the local enrichment zone produced particle precursors that form aggregated particles. Therefore, at 1800 rpm, the particles presented a bimodal distribution, and the peak particle diameter of nucleation particles moved towards the large particle diameter. However, when the engine speed further increased, the increase in airflow motion intensity made the mixture more homogeneous. The wall oil film and the local enrichment area were reduced, and the possibility of forming aggregated particles was reduced. Thus, the particles were distributed in a single peak.
When ABEDIr was 20%, the particles showed a unimodal distribution at all engine speeds. The peak particle diameter was 13.3 nm at 1000 and 1400 rpm, but 15.4 nm at other engine speeds. As mentioned above, when 20% ABE was added, the OH radical in ABE limited the generation of PAHs, which formed aggregation particles through surface growth. Therefore, the particles under 20% ABEDIr presented unimodal distribution, and the proportion of the accumulation particles was relatively low. It also indicates that ABE can inhibit the formation of accumulation particles. It can also be seen from the figure that the peak particle diameter of nucleation particles increases with the increase in engine speed, which is due to the increase in in-cylinder temperature with the increase in engine speed. Although the formation of accumulation particles is inhibited by ABE, the increase in in-cylinder temperature leads to the development of particles with larger particle diameters.
Figure 15 shows the particle number with MAP and different ABEDI ratios at the engine speed of 1800 rpm. When ABEDIr was 0%, 20%, and 40%, the NPN, APN, and TPN continued to increase with the increase in MAP, especially for pure gasoline. At low ABEDIr, gasoline was the main component of the in-cylinder fuel. With the increasing MAP, the fuel injection amount increased greatly. The local fuel enrichment area increased which promoted the formation of nucleation and surface growth of the particle precursors, resulting in a continuous increase in particle numbers. Although increasing MAP can improve the in-cylinder thermal atmosphere to promote fuel evaporation, the gasoline was injected by the port injection system, but the improvement of the evaporation effect was limited.
It also shows that when the ABEDIr = 60%, 80%, and 100%, PN reaches low levels at all loads. When ABEDIr was 60%, the TPN first increased and then decreased with the increase in MAP. Contrary to ABEDIr of 0–40%, particle numbers decreased at high MAP. The in-cylinder thermodynamic atmosphere of higher MAP can fully evaporate a large proportion of ABE. Fuel oxygen of ABE fuel can inhibit particle precursors and promote particle oxidation. When ABEDIr reached 80% and 100%, the particle numbers decreased slightly and then remained unchanged with the increase in MAP. The particle numbers were all lower than 4 × 104 n/cm3 at different loads. This is because, when the in-cylinder components consist of a large proportion of ABE or pure ABE, the fuel oxygen has a very significant effect on inhibiting the nucleation of particle precursors. Meanwhile, the reduction in the gasoline ratio also reduced the PAHs carried by the fuel, which further reduced the probability of the nucleation of particle precursors. Compared to low ABEDIr, the particles were no longer sensitive to MAP at high ABEDIr, indicating that the oxygen-containing groups of ABE had an overwhelming effect on the oxidation of particles. Overall, to control the particle number, at least 60% of ABEDIr must be adopted at medium and high loads.
As can be seen from the above, the higher the MAP, the higher the particle emissions. Therefore, as shown in Figure 16, we continued to explore the effect of adding ABE on particle size distribution at MAP = 60 and 70 kPa. When MAP = 60 kPa, the particle size distribution gradually changed from a bimodal distribution to a unimodal distribution with the increase in ABEDIr. When the ABEDIr was 80% and 100%, the particle size distribution became a line close to the horizontal axis. This phenomenon indicated that the formation of accumulation particles was inhibited by increasing ABEDIr. The oxygen-containing groups of ABE had strong oxidation effects on both nucleation and accumulation particles, but the low combustion temperature of ABE reduced the possibility of fuel pyrolysis at a high temperature to form aggregation particles. Therefore, with the increase in ABEDIr, the particles became smaller in diameter and lower in concentration.
It can be seen from Figure 16b that the particle size presented an obvious bimodal distribution at MAP = 70 kPa, which was different from that at 60 kPa. At high MAP, the high fuel injection amount led to the local fuel enrichment area, and the fuel pyrolysis formed large-size particles at higher in-cylinder temperature. Even when the ABEDIr reached 80% and 100%, the particles still showed a bimodal distribution, which was mainly composed of accumulation particles, but the particle number was very small. This is because when ABEDIr is high, the high pulse width of direct injection increases the penetration distance of the ABE spray, increasing the probability of fuel impact to form an oil film, while the low-temperature diffusion combustion of the wet oil film forms accumulation particles. In general, a large proportion of ABE fuel at higher loads can be very effective in improving particle emissions.

4. Conclusions

In this paper, the combustion and emissions of a GPI + ABEDI engine at different loads and speeds were investigated using the combined injection SI engine test bench. The engine operating conditions included different speeds of 1000, 1400, 1800, 2200, and 2600 rpm when the MAP = 50 kPa, and the MAP of 30, 40, 50, 60, and 70 kPa when the speed = 1800 rpm. The range of ABEDIr contained 0, 20%, 40%, 60%, 80%, and 100%. The main conclusions of the experiment are as follows:
  • In a fixed engine MAP = 50 kPa, when the engine speed was 1000–1800 rpm, 80% of ABEDIr can make the engine’s IMEP maximum. At the engine speeds of 2200 and 2600 rpm, 100% ABEDIr can reach the best IMEP. In the study with a fixed engine speed = 1800 rpm, when MAP = 30, 40, and 50 kPa, IMEP reached the maximum value at ABEDIr of 60%, 80%, and 80%, respectively. When the engine ran under loads of MAP = 60 and 70 kPa, IMEP increased continuously with the increase in ABEDIr, which suggests that pure ABE can attain better dynamic performance than gasoline;
  • In a fixed engine MAP = 50 kPa, at all speeds, 60% ABEDIr can achieve the best HC and NOx emissions. The CO emissions were the best when the ABEDIr was 100%. In the study of fixed engine speed = 1800 rpm, the NOx emissions reached the lowest when the ABEDIr was 60%. When the ABEDIr was between 60% and 100%, HC emissions were less than half of those of pure gasoline. However, only when ABEDIr was greater than or equal to 80%, could the CO emissions be lower than those of gasoline;
  • In the study of fixed engine MAP = 50 kPa, when ABEDIr was 60–100%, PN at the speed of 1800–2600 rpm was much lower than that of pure gasoline. In the study of a fixed engine speed = 1800 rpm, when ABEDIr was 0–40%, the NPN, APN, and TPN increased continuously with the increasing MAP. When the ABEDIr was 60–100%, PN reached very low levels at a MAP of 30–70 kPa, which is lower than 4 × 104 n/cm3 at 80% and 100% ABEDIr. At least 60% ABEDIr should be used to control PN at medium and high loads;
  • Overall, at low engine speeds and low loads, the dynamic performance of 80% ABEDIr was optimal. At higher speeds and loads, ABEDIr = 100% was optimal if the power performance was the main demand; otherwise, 80% ABEDIr can be selected to control emission performance and power performances at all operating states;
  • According to the above research contents, it can be proved that a higher proportion of ABE in-cylinder direct injection can be applied to the engine instead of gasoline under many engine working conditions, which can bring great power performance and emissions performances.

Author Contributions

Conceptualization, X.Y. and Z.G.; Data curation, Z.G.; Formal analysis, X.Y. and Z.G.; Investigation, J.Z. (Jiahua Zhang); Methodology, X.Y.; Project administration, D.L.; Supervision, X.Y. and Y.L.; Writing—original draft, J.Z. (Jufang Zhang); Writing—review & editing, Z.G. All authors have read and agreed to the published version of the manuscript.

Funding

This work was supported by the Young Elite Scientists Sponsorship Program by CAST (Grant No. 2021QNRC001), the National Natural Science Foundation of China (Grant No. 51976076), and the Scientific and Technological Developing Scheme of Jilin Province (No. 20220508007RC).

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Conflicts of Interest

The authors declare no conflict of interest.

Nomenclature

SISpark ignitionMAPIntake manifold absolute pressure
CACrank angleIMEPIndicated mean effective pressure
GPIGasoline port injectionλExcess air ratio
NOxNitrogenMBTMinimum advance for best torque
COCarbon monoxideBTDCBefore top dead center
HCHydrocarbonPNParticle number
ABEDIABE direct injectionTPNTotal particle number
ABEDIrABE direct injection ratioAPNAccumulation mode particle number
LHVLower heating valueNPNNucleation mode particle number
LFSLaminar flame speed LHOVLatent heat of vaporization
CA0-90The duration of the CA from ignition to 90% heat release
CICompression ignitionABEAcetone-butanol-ethanol
DITDirect injection timingPAHsPolycyclic aromatic hydrocarbons
BTEBrake thermal efficiencyPFIPort fuel injection
BSFCBrake specific fuel consumptionrpmRevolutions per minute

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Figure 1. Schematic diagram of in-cylinder structure and injector of the test engine.
Figure 1. Schematic diagram of in-cylinder structure and injector of the test engine.
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Figure 2. Schematic diagram of the experimental setup.
Figure 2. Schematic diagram of the experimental setup.
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Figure 3. Variation in CA0-90 with engine speeds under different ABEDIr.
Figure 3. Variation in CA0-90 with engine speeds under different ABEDIr.
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Figure 4. Changes in CA0-90 with ABEDIr under different MAP.
Figure 4. Changes in CA0-90 with ABEDIr under different MAP.
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Figure 5. Variation in IMEP with ABEDIr at different engine speeds.
Figure 5. Variation in IMEP with ABEDIr at different engine speeds.
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Figure 6. Variation in IMEP with ABEDIr under different MAP.
Figure 6. Variation in IMEP with ABEDIr under different MAP.
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Figure 7. Variation in NOx emissions with engine speeds at different ABEDIr.
Figure 7. Variation in NOx emissions with engine speeds at different ABEDIr.
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Figure 8. Change in NOx emissions with MAP under different ABEDIr.
Figure 8. Change in NOx emissions with MAP under different ABEDIr.
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Figure 9. Variation in HC emissions with engine speeds under different ABEDIr.
Figure 9. Variation in HC emissions with engine speeds under different ABEDIr.
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Figure 10. Variation in HC emission with MAP under different ABEDIr.
Figure 10. Variation in HC emission with MAP under different ABEDIr.
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Figure 11. Variation in CO emission with engine speeds under different ABEDIr.
Figure 11. Variation in CO emission with engine speeds under different ABEDIr.
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Figure 12. Variation in CO emission with MAP under different ABEDIr.
Figure 12. Variation in CO emission with MAP under different ABEDIr.
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Figure 13. Variation in particle number with ABEDIr at different engine speeds.
Figure 13. Variation in particle number with ABEDIr at different engine speeds.
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Figure 14. Variation in particle size distribution with engine speed at different ABEDIr.
Figure 14. Variation in particle size distribution with engine speed at different ABEDIr.
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Figure 15. Variation in particle number with MAP under different ABEDIr.
Figure 15. Variation in particle number with MAP under different ABEDIr.
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Figure 16. Variation in particle size distribution with ABEDIr at different MAP.
Figure 16. Variation in particle size distribution with ABEDIr at different MAP.
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Table
Table 1. Main technical parameters of the engine.
Table 1. Main technical parameters of the engine.
Engine TypeSpark Ignition, Four Cylinder, Combined Injection
Compression ratio9.6:1
Displacement1.984 L
Bore × stroke82.5 × 92.8 mm
Maximum power137 kW (5000 rpm)
Maximum torque320 N·m (1600–4000 rpm)
Table
Table 2. The test equipment parameters.
Table 2. The test equipment parameters.
Measured ParametersEquipment ModelMeasuring AccuracyMeasuring RangeUncertainty (%)
TorqueCW160≤±0.28 N·m0–600 N·m±2
SpeedCW160≤±1 rpm0–6000 rpm±0.07
Cylinder pressureAVL-GU13Z-24≤±0.5%0–20 MPa±0.5
Crank angle (CA)Kistler-2614B≤±0.5°0–720°±0.07
Excess air ratio (λ)LAMBDA LA4≤±0.10.700–32.767±1
COAVL-GAS 1000≤±0.01%0–15% vol±3.5
HCAVL-GAS 1000≤±1 ppm0–30,000 ppm vol±3.5
NOxAVL-GAS 1000≤±1 ppm0–5000 ppm vol±2
Particle numberDMS 500≤±1.4 × 104 dN/dlgDp(cm3)0–1011 dN/dlgDp(cm3)±1
Gasoline mass flow rateOno Sokki DF-2420≤±0.01 g/s0.2–82 kg/h±0.03
Table
Table 3. Fuel physicochemical properties [33,40,46,47,48,49].
Table 3. Fuel physicochemical properties [33,40,46,47,48,49].
AcetoneButanolEthanolABE (3:6:1)Gasoline
Chemical formulaC3H6OC4H9OHC2H5OHC3.5H8.4OC4-C12
Research octane number11796100102.788–99
C/H atom ratio0.500.400.330.420.44
Oxygen content (wt.%)27.621.634.824.7—
Density at 288 K (kg/m3)791813795804.6770
LHV (MJ/kg)29.633.126.831.443.5
LHOV at 298 K (kJ/kg)518582904595380–500
Stoichiometric air–fuel ratio9.511.29.010.514.7
Laminar flame speed (cm/s)34 B48 C48 C37 B33–44 A
Note: pA = 1 atm, T = 298–358 K, λ = 1; pB = 1 atm, T = 298 K, λ = 1; pC = 1 atm, T = 343 K, λ = 1.
Table
Table 4. Engine test conditions and experimental variables.
Table 4. Engine test conditions and experimental variables.
Variable ValuesEngine Test Conditions
Part IEngine speed = 1000, 1400, 1800, 2200, 2600 rpm

ABEDIr = 0, 20%, 40%, 60%, 80%, 100%		λ = 1.0
Ignition timing = MBT
PFI injection timing = 340 °CA BTDC
PFI pressure = 0.3 MPa
ABEDI injection timing = 300 °CA BTDC
ABEDI injection pressure = 9 MPa
MAP = 50 kPa
Part IIMAP = 30, 40, 50, 60, 70 kPa

ABEDIr = 0, 20%, 40%, 60%, 80%, 100%		λ = 1.0
Ignition timing = MBT
PFI injection timing = 340 °CA BTDC
PFI pressure = 0.3 MPa
ABEDI injection timing = 300 °CA BTDC
ABEDI injection pressure = 9 MPa
Engine speed = 1800 rpm
Table
Table 5. Definition and total energy change in fuels with different ABEDIr.
Table 5. Definition and total energy change in fuels with different ABEDIr.
G100
(Pure Gasoline)		ABE20ABE40ABE60ABE80ABE100
(Pure ABE)
ABEDIr0%20%40%60%80%100%
GPI ratio100%80%60%40%20%0%
Total energy change0%0.2%0.4%0.6%0.8%1%
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Zhang, J.; Yu, X.; Guo, Z.; Li, Y.; Zhang, J.; Liu, D. Study on Combustion and Emissions of a Spark Ignition Engine with Gasoline Port Injection Plus Acetone–Butanol–Ethanol (ABE) Direct Injection under Different Speeds and Loads. Energies 2022, 15, 7028. https://doi.org/10.3390/en15197028

AMA Style

Zhang J, Yu X, Guo Z, Li Y, Zhang J, Liu D. Study on Combustion and Emissions of a Spark Ignition Engine with Gasoline Port Injection Plus Acetone–Butanol–Ethanol (ABE) Direct Injection under Different Speeds and Loads. Energies. 2022; 15(19):7028. https://doi.org/10.3390/en15197028

Chicago/Turabian Style

Zhang, Jufang, Xiumin Yu, Zezhou Guo, Yinan Li, Jiahua Zhang, and Dongjie Liu. 2022. "Study on Combustion and Emissions of a Spark Ignition Engine with Gasoline Port Injection Plus Acetone–Butanol–Ethanol (ABE) Direct Injection under Different Speeds and Loads" Energies 15, no. 19: 7028. https://doi.org/10.3390/en15197028

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