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Article

Impact of Bioethanol Concentration in Gasoline on SI Engine Sustainability

by
Alfredas Rimkus
*,
Saugirdas Pukalskas
,
Gabrielius Mejeras
and
Saulius Nagurnas
Department of Automobile Engineering, Faculty of Transport Engineering, Vilnius Gediminas Technical University, Plytinės Str. 25, 10105 Vilnius, Lithuania
*
Author to whom correspondence should be addressed.
Sustainability 2024, 16(6), 2397; https://doi.org/10.3390/su16062397
Submission received: 9 February 2024 / Revised: 7 March 2024 / Accepted: 11 March 2024 / Published: 14 March 2024
(This article belongs to the Section Energy Sustainability)
Browse Figures
Versions Notes

Abstract

:
This study presents an experimental investigation into the impact of blending bioethanol (E100) with conventional gasoline (E0), incrementally increasing biofuel levels up to E10, E50, and E70. The test was carried out in two stages: Stage I assessed the engine’s performance under fixed speeds (n = 2000 rpm and n = 2500 rpm) and fixed throttle positions (15%, 20%, and 25%) to measure changes in engine torque, efficiency, and environmental metrics by varying the concentration of bioethanol in the fuel. Stage II aimed to enrich the initial findings by conducting an additional test, running the engine at a fixed speed (n = 2000 rpm) and braking torque (MB = 80 Nm) and varying the ignition timing. Results indicated slight improvements in engine brake torque and thermal efficiency (up to 1.7%) with bioethanol content increased to 70%, and a notable reduction in incomplete combustion byproducts—carbon monoxide and hydrocarbons emissions (up 15% and 43%). Nitrogen oxide emissions were reduced by up to 23%, but carbon dioxide emissions decreased by a mere 1.1%. In order to increase thermal efficiency by adding higher bioethanol blend concentrations, adjusting the ignition timing to counter the longer ignition delay is necessary; however, higher emissions of nitrogen oxides and hydrocarbons are a major drawback of such a strategy. The results of the research are important in determining the optimal concentration of bioethanol in the mixture with gasoline for the energy and environmental sustainability of a spark ignition engine.

1. Introduction

The Paris Agreement, a landmark agreement to combat climate change, sets out an imperative: countries must develop and implement strategies to reduce emissions across all sectors, with transport under particular scrutiny [1]. As nations strive to meet their commitments under this agreement, the spotlight is increasingly on the transport industry. This sector is not only a significant contributor to global emissions but also a critical focus for pioneering sustainable and environmentally responsible solutions [2,3,4]. In this context, the use of cleaner and more sustainable fuels [5,6,7,8], increased energy efficiency [9,10], and the incorporation of cutting-edge technologies to reduce the environmental impact of transport have emerged as central pillars in the transition to a greener future. Among these solutions, bioethanol stands out as the cornerstone, offering a multi-faceted approach to addressing the common challenges of sustainable transport [11,12,13,14,15].
The use of ethanol in transport can significantly reduce CO2 emissions: 15–30% ethanol petrol blends can reduce CO2 emissions by between 7.2 and 13.4% [16]. Increasing ethanol content in petrol is therefore necessary to increase CO2 neutrality of transport; however, the majority of countries currently use a proportion of only 10% in the blends.
Ethanol can be used in both spark-ignition and compression-ignition engines [17]. However, while spark-ignition engines use a wide range of petrol/ethanol blends, from very low content to pure ethanol, a relatively small proportion of ethanol can be added in compression-ignition engines [18,19,20].
As the global movement towards sustainable fuels continues to gain momentum, scientists in the US are looking at growing emission levels from the transport sector [21]. Their comprehensive analysis assesses the environmental impact of producing bioethanol from different feedstocks, with a focus on global availability. The results paint a compelling picture for the use of waste-based feedstocks, which have minimal environmental impact and offer a potential solution to the perennial food versus fuel debate. Not only do waste feedstocks reduce material consumption and land use compared to agricultural feedstocks, but they also fit seamlessly with the broader goals of sustainability and emissions reduction [22]. Scientists from China present an innovative method for bioethanol production from apple wood residue [23]. Their research not only demonstrates the potential of apple wood residue as a sustainable source of bioethanol but also the adaptability and versatility of bioethanol in different production contexts.
The addition of ethanol as a gasoline additive in spark-ignition engines, where the air–fuel mixture is prepared in the carburetor, leads to a slight reduction in engine power and torque due to the air–fuel mixture becoming leaner [24]. However, engines equipped with a multi-point fuel injection system exhibit the opposite effect, resulting in a slight increase in engine torque and brake power [25]. The brake-specific fuel consumption increases in both cases due to the lower calorific value of ethanol. Nevertheless, when taking into account the fuel mass and calorific value, the energy consumption among all mixtures and pure petrol appears to be remarkably similar [26].
Otto engines with a carburetor show a significant reduction in NOx emissions that is directly proportional to the percentage of ethanol in the ethanol/petrol mixture. This comes as a result of decreasing combustion temperature [24] but leads to increased emissions of CO and HC. Engines equipped with a multi-point fuel injection system running on an ethanol/petrol mixture demonstrate lower emissions of CO and HC but significantly higher emissions of CO2. NOx emissions in such engines remain relatively stable at lower revs and torque levels; however, under elevated loads, there is a discernible rise in NOx emissions [25]. Thus, modern fuel injection systems and bioethanol’s cooling effect have an impact on reducing CO and CO2 emissions, contrasting with general trends noted in older engine technologies with carburetors. This demonstrates the efficiency of advanced engines in optimizing combustion with bioethanol blends. Bioethanol, which contains oxygenates, increases octane content in petrol and plays an important role in reducing particulate matter emissions [27,28].
The aim of this paper is to highlight the positive attributes of bioethanol and justify its potential for use in a broad transportation context. Also, it aims to analyze some of the nuances that lead to significant differences in operation under different conditions. Some studies have shown that the use of an ethanol additive increases specific fuel consumption compared to pure gasoline [29], while other studies have shown the opposite—decreased fuel consumption [30]. There were studies showing that ethanol can affect the spray characteristics of fuels [31]. For example, a blend of 20% ethanol and aviation kerosene is an ideal alternative fuel for aircraft engines that improves atomization performance and therefore has a high potential for use in aircraft engines. Bioethanol (or bioethanol/kerosene blends) can be used not only in jet engines but also in pulse engines for aerospace applications [32]. The work by Liu and others illustrates how ethanol biofuel uniquely addresses two pressing challenges: oil security and CO2 emissions [33]. Given the aviation industry’s heavy reliance on imported kerosene, securing a stable and sustainable supply of oil is of paramount importance while also reducing carbon emissions to meet stringent environmental sustainability targets. Biofuel ethanol derived from renewable biomass is emerging as a viable solution that offers a twofold remedy by reducing dependence on finite petroleum resources and reducing greenhouse gas emissions. Research by scientists at Tianjin University presents innovative ethanol-to-jet fuel processes that combine corncob gasification, syngas fermentation, and ethanol conversion. A life cycle assessment underlines the benefits of corncob gasification combined with fermentation, highlighting the potential for reduced emissions and cleaner production methods [34]. These findings are equally promising for the road transport sector, where ethanol-based fuels can serve as a promising option to reduce reliance on fossil fuels and cut emissions from spark ignition engines.
In pursuit of sustainability, it is crucial to consider the compatibility and feasibility of different bioethanol concentrations within existing systems. The use of different bioethanol concentrations provides an opportunity to identify optimal blend ratios that balance performance, fuel economy, and emissions [35]. This knowledge is instrumental in shaping guidelines for utilizing higher bioethanol blends, especially in older vehicle fleets or regions where these blends are common. It helps not only to establish usage standards, but also to refine engine performance in order to enhance overall efficiency in sustainable transport.
Nevertheless, notwithstanding the enumerated favorable attributes of ethanol and its positive impact on fuel emissions and efficiency, recent scientific review articles reveal inconsistencies in the findings of certain studies [35,36]. Therefore, the objective of our study is to reassess and substantiate the impact of ethanol–gasoline blends on emissions, brake thermal efficiency, and other parameters in spark ignition engines.
Evaluating the presented research requires attention to its practical importance and the prospective advantages within its specific context, with the assumption that the insights provided will lead to specific improvements in the areas of sustainable transport methodology. While the concept of using ethanol as an alternative fuel has already been established, ongoing experimentation with various bioethanol concentrations is crucial, providing valuable insights into combustion dynamics, system compatibility, and the advancement of cleaner, sustainable transportation options. These investigations not only deepen our understanding of alternative fuel processes but also contribute to the evolving narrative of bioethanol as a viable, eco-friendly energy source, marking a significant stride toward sustainable transport. It is also important to emphasize that a scientific study is a gradual process, building upon existing knowledge. New discoveries in this realm are often made from nuanced details, empirical findings, and refinement techniques.

2. Research Methodology

The impact of bioethanol on the performance of an internal combustion engine was assessed by conducting bench tests on the HR 16DE spark ignition engine from Nissan Qashqai (refer to Table 1). The HR 16DE spark ignition engine is installed in the VilniusTech laboratory on the engine test bench. Renault still manufactures this engine model, building on its innovation, high quality, and reliability.
Experimental tests were conducted in two distinct stages, each designed to evaluate various engine performance parameters under controlled conditions. In Stage I, the engine’s throttle opening was fixed at three different positions (15%, 20%, 25%). The engine’s shaft rotation speed (n) and ignition timing (Θ) were set to specific values. Specifically, when the engine speed was set to n = 2000 rpm, the ignition timing was maintained at Θ = 20° Crank Angle (CA) before Top Dead Center (bTDC). Similarly, when the engine speed was adjusted to n = 2500 rpm, the ignition timing was set at Θ = 24° CA bTDC. This allowed for the assessment of key parameters, including Brake Torque (MB), Brake Specific Fuel Consumption (BSFC), and both energy and ecological indicators, while keeping the throttle opening constant. In Stage II, the engine operated at a consistent engine load, maintaining a Brake Mean Effective Pressure (BMEP) of 0.62 MPa by adjusting the Brake Torque to 80 Nm. In this stage, the ignition timing (Θ) was systematically altered, ranging from Θ = 16° CA bTDC to Θ = 32° CA bTDC. Stage II enabled a more accurate assessment of the engine’s energy and ecological performance indicators while keeping the engine load fixed.
The engine testing setup, as illustrated in Figure 1, comprises essential components for precise control and measurement. The engine was controlled by the MoTeC M800 programmable electronic control unit (ECU). The engine load (MB) was created using an eddy current-type AMX 200/100 load stand with a maximum speed of 6000 rpm and a peak torque capacity of 480 Nm, demonstrating remarkable accuracy of ±0.9 Nm. Fuel consumption was calculated meticulously, using an electronic–gravitational fuel consumption scale AMX 212F, which provides measurement capabilities within the range of 0.01 to 50 kg/h and ensures precision at ±0.1%. To measure air consumption accurately, the air mass meter BOSCH HFM 5 was used, allowing measuring within the limits of 8 to 370 kg/h, with an accuracy of ±2%. The temperature of exhaust gases was measured using a K-type thermocouple sensor, offering measurement capabilities ranging from 0 to +1250 °C and an accuracy of ±0.5%. Emissions analysis was performed using the AVL DiCom 4000 exhaust gas analyzer, measuring limits for CO2 (0 to 20%, with an accuracy of ±0.1%), CO (0 to 10%, with an accuracy of ±0.01%), HC (0 to 20,000 ppm, with an accuracy of ±1 ppm), NOx (0 to 5000 ppm, with an accuracy of ±1 ppm), and O2 (0 to 25%, with an accuracy of ±0.01%).
A variety of fuels were used in both stages of the tests, from pure gasoline (E0) to various gasoline–bioethanol blends (E10, E30, E50, E70). A stoichiometric mixture with an excess air ratio of λ = 1.0 was consistently maintained to ensure standardized conditions and reliable data collection during bench tests. To prepare the fuel blends, gasoline was mixed with bioethanol. Table 2 lists the properties of pure fuels. Bioethanol stands out with a significantly lower carbon content, resulting in a reduced carbon-to-hydrogen (C/H) ratio compared to gasoline. This unique biofuel also has a notable oxygen content, serving as an effective oxidizer during combustion, ultimately enhancing combustion efficiency. Bioethanol exhibits a considerably lower heating value compared to gasoline, burning at slightly lower temperatures but at an accelerated rate. Moreover, when bioethanol enters the intake manifold, it has a higher cooling effect within the cylinder during the evaporation process due to its significantly higher (2–3 times) latent heat of evaporation. Additionally, bioethanol exhibits greater resistance to detonation during combustion, contributing to improved engine safety and performance.
The main properties of the fuel blends used in the experiments (E10, E30, E50, and E70) were calculated on the basis of the information of pure fuels. The properties are listed in Table 3. Increasing bioethanol concentration in the blend with gasoline results in a significant decrease in the carbon mass fraction and a great increase in the oxygen mass fraction of the fuel blend, resulting in a notable change in fuel properties. Table 3 also shows the differences in the properties of E70 compared to E0 (ΔE70, %). Changes in fuel properties also change the combustion process, which is why it is important to adjust ignition timing during testing.

3. Results and Discussion

3.1. Energy Performance

Following the initial stage of our study, which involved varying throttle openings (Stage I), we observed a marginal increase in the engine brake torque (MB) and the Brake Mean Effective Pressure (BMEP) as we increased the bioethanol concentration in the fuel blend (Figure 2). Specifically, when the engine ran on E70 fuel blend, MB and BMEP exhibited a consistent rise of up to 1.7% compared to E0. This was due to multiple factors. On one hand, the use of bioethanol reduces the Lower Heating Value (LHV) of the fuel blend, so a unit mass of E70 delivers approximately 27.1% less energy, as shown in Table 3. On the other hand, bioethanol is rich in oxygen, which partially replaces the oxygen contained in the air that plays an active role in combustion, and 1 kg of fuel requires ~27.6% less air. Therefore, when the engine is running on a stoichiometric mixture, the same mass of air is injected with a 27.6% higher mass of E70 fuel. Another noteworthy factor is the latent heat of evaporation, as bioethanol enhances the cooling effect on intake air, increasing its density and intake mass during the cycle, thereby facilitating an additional boost in fuel mass and energy. In summary, the rise in MB and BMEP is due to better distribution of fuel energy in the cylinder, as well as more efficient combustion of bioethanol. It is worth noting that when the engine’s rotational speed was elevated from 2000 rpm to 2500 rpm, a decrease in both MB and BMEP was observed due to reduced volumetric efficiency. However, this phenomenon became less pronounced with wider throttle openings, as the mixture of intake air and fuel gained greater inertia, ultimately improving volumetric efficiency.
Bioethanol has a higher octane content compared to conventional gasoline (Table 2), but the engine used in the experimental study is not optimized for fuels with higher octane contents (without the option of increasing the compression ratio), and therefore, the benefits of bioethanol are only partially realized. Bioethanol has different combustion characteristics, such as ignition delay and rate of combustion, compared to gasoline. These differences were preliminarily assessed in Stage II of the study by adjusting ignition timing.
Significant variations in performance indicators become evident when analyzing the specific fuel mass consumption (BSFC_m). In Stage I, the bioethanol concentration was gradually increased to 10%, 30%, 50%, and 70%, resulting in consistent BSFC_m increases of approximately 3.5%, 11%, 19%, and 27%, compared to E0 (Figure 3). The primary driver of these changes is the diminishing LHV of the fuel blend. Although some studies have documented the opposite effect, when the ethanol content is increased, the specific fuel consumption decreases [30]. In addition, as the throttle was opened, the specific fuel mass consumption gradually decreased, as a result of enhanced engine power output and improved thermal efficiency. In Stage II of the study, the ignition timing was varied (Θ) while maintaining fixed engine load (MB = 80 Nm) and consistent BMEP (0.62 MPa). It was determined that BSFC_m for all tested fuels reached its minimum when the ignition timing Θ was set between 24–26° CA bTDC. Despite the faster combustion characteristics of bioethanol (Table 2), increasing the concentration of bioethanol did not require a later start of combustion. This is attributed to the cooling effect of bioethanol on the fuel–air mixture and the higher auto-ignition temperature, which accounts for one of the longer ignition delays within the gasoline–bioethanol blend [42].
The specific fuel volume consumption (BSFC_V) indicator is significant, especially considering the fact that fuel procurement is based on volume. In Stage I, the incremental increase in bioethanol concentration (E10, E30, E50, and E70) consistently resulted in BSFC_V increments of approximately 3.1%, 9.3%, 15.8%, and 22.5%, compared to E0 (Figure 4). It should be noted that with an increase in bioethanol concentration, the specific volumetric consumption of the fuel mixture increases more moderately compared to the specific mass consumption of fuel, due to a ~7.3% higher density of bioethanol compared to gasoline. The results of Stage II of the study reaffirm the differences in fuel consumption and the combustion characteristics of bioethanol-enhanced fuels discussed earlier. A higher combustion speed of bioethanol does not require later ignition timing, as the evaporation characteristics of bioethanol result in a lower temperature of the air–fuel mixture and a greater ignition delay [43].
The Break Thermal Efficiency (BTE) serves as a key indicator of the conversion of fuel thermal energy into engine mechanical energy. Figure 5 illustrates the notable enhancement in overall performance achieved by introducing higher bioethanol concentrations into fuel blends. Other studies show similar trends [25,29,30]. However, research by Verma reveals that there is no linear relationship between the improvement in BTE and the amount of ethanol, and a small amount of ethanol is enough to significantly improve BTE, while further increases in the amount of ethanol have a smaller effect [43]. This improvement is primarily due to the increased oxygen concentration, which facilitates a more efficient combustion process in the cylinder. The improved combustion is confirmed by the significant reduction in specific emissions of carbon monoxide and hydrocarbons (Figures 8 and 9).
In Stage I of the study, a gradual increase in the concentration of bioethanol in the fuel yields incremental BTE improvements of approximately 0.6%, 0.9%, 1.3%, and 1.7%, compared to E0. Increasing the concentration of bioethanol resulted in a significant increase in BSFC_m (Figure 3) but a proportional decrease in fuel LHV, while a higher torque (Figure 2) led to an increase in BTE. Even when the engine runs on lean mixtures, a certain amount of ethanol significantly improves operating efficiency [44,45]. In Stage II of the study, where the engine load was kept constant (BMEP = 0.62 MPa), it is evident that fuel blends with higher bioethanol contents have higher BTE values when the ignition timing is advanced. The engine running on gasoline achieves maximum efficiency (BTE = 0.335) at ignition timing Θ = 24 CA bTDC, with fuel blend E70 at Θ = 26 CA bTDC BTE = 0.337. This adjustment is likely to compensate for the prolonged ignition delay associated with the lower in-cylinder temperature at the end of the compression stroke and the higher auto-ignition temperature of the bioethanol (Table 2).
Exhaust Temperature (Tex), as depicted in Figure 6, demonstrates a noticeable decrease (~0.27%, ~0.72%, ~1.2%, and ~1.9%) with the introduction of bioethanol into the fuel blend. This reduction in exhaust gas temperature is associated with higher BTE, indicating improved energy conversion. The lower exhaust temperature is primarily attributed to a slightly faster burning rate of bioethanol compared to E0, as well as its lower flame temperature, as outlined in Table 2. During Stage I of the study, an increase in Tex was observed with wider throttle openings, but this does not imply reduced thermal efficiency. Instead, it reflects the larger energy content within the cylinders. In this case, more of this energy is converted into efficient mechanical work for the engine. In all cases, the bioethanol additive consistently lowers Tex across various throttle openings and engine speeds. In Stage II of the study, advancing ignition timing results in Tex reduction, signifying earlier combustion completion and greater conversion of combustion energy into useful work. However, excessively early ignition (Θ > 24–26° CA bTDC) leads to diminishing BTE as a significant portion of the fuel combustion energy dissipates through the cooling system. In this scenario, the ethanol additive, which lowers combustion temperatures, becomes more impactful [46].

3.2. Environmental Performance

As the bioethanol concentration gradually increases to 70%, specific CO2 emissions decrease by approximately 0.5%, 0.7%, 0.8%, and 1.1%, respectively (Figure 7). With an increase in bioethanol concentration to 70%, the E70 C/H ratio decreases by ~25% (Table 2). A more substantial decrease in CO2 emissions could be expected; however, the 26% increase in fuel consumption (Figure 3) exerts a counteractive effect. It is important to note that CO2 is a product of complete combustion, and its emission increases as combustion efficiency improves. However, not all studies show the same trends. For example, research by Yusuf reveals that gasoline with a 5% ethanol blend has the highest CO2 emissions, even higher than pure gasoline or other blends [30]. Understanding the intricate relationship between fuel composition and emissions is pivotal for optimizing both environmental sustainability and engine performance. In Stage I of the study, a notable increase in specific CO2 emissions was observed when the throttle opening was set at 15% and n = 2500 rpm. This can be attributed to reduced brake torque (Figure 2), owing to the engine’s poorer volumetric efficiency. In such cases, the addition of bioethanol yields a more pronounced positive effect. In Stage II of the study, it becomes apparent that the lowest CO2 emissions coincide with achieving the highest BTE. For E70, advancing ignition timing by approximately 2° CA compared to E0 due to the extended ignition delay phase results in a more efficient reduction in CO2 emissions. Additionally, it is noteworthy that bioethanol qualifies as a renewable fuel and, in the context of a life cycle assessment, E100 CO2 emissions are approximately 60% lower compared to fossil-based gasoline [7].
Carbon monoxide (CO) specific emissions, as illustrated in Figure 8, serve as indicators of incomplete combustion. An inverse relationship is observed between bioethanol concentration in the blend and CO production. Gradual increases in bioethanol concentration up to 70% yield reduced CO emissions of approximately 3.8%, 8.9%, 13.7%, and 16.7%, respectively. This correlation can be attributed to bioethanol’s oxygen content, which enhances combustion efficiency as oxygen levels rise in the blend. Additionally, a lower C/H ratio plays a role (Table 3). This is consistent with the results of studies that have been conducted by other researchers [6,17]. The results of Stage I confirm that as the throttle opening increases, resulting in higher MB and BTE, the specific CO emissions of E0 decrease slightly significantly compared to the reduction in CO emissions of the E70 blend. A higher BSFC and lower combustion temperature of E70 are likely contributing factors in this context. Stage II confirms the positive impact of bioethanol in reducing the concentration in fuel and shows that the lowest specific CO emission is achieved at the same ignition time, corresponding to the point of maximum BTE and the lowest fuel consumption.
Hydrocarbons (HCs) are byproducts of incomplete combustion, typically arising from uneven fuel–air mixing and the extinguishing of the flame front in various zones of the combustion chamber. Bioethanol plays a crucial role in enhancing oxygen delivery during the combustion process, thereby optimizing combustion outcomes and reducing the emission of incomplete combustion products. With an increase in bioethanol concentration to 70%, specific HC emissions exhibit a significant decrease of approximately 8.2%, 19.7%, 32.0%, and 43.5% (Figure 9). In Stage I of the study, it became evident that as the throttle opening and engine brake torque increase, specific HC emissions decrease more pronouncedly in fuels with lower bioethanol concentrations. This observation correlates with CO emissions, suggesting that the greater reduction in emissions of these incomplete combustion products at higher throttle openings is constrained by the higher BSFC and lower combustion temperature of E70 fuel. In Stage II of the study, it was determined that when altering the ignition timing, the behavior of specific HC emissions differs from that of CO emissions. Advancing the ignition timing from Θ = 16° CA bTDC to Θ = 32° CA bTDC leads to a gradual increase in HC emissions. Early combustion initiation results in elevated HC emissions, as combustion starts before the fuel–air mixture is fully homogenized. This pattern holds for all investigated fuel blends, but it was observed that with a higher concentration of bioethanol, the increase in HC emissions occurs with lower intensity, affirming bioethanol’s role in facilitating the preparation of a more uniform and complete burning mixture [45].
Nitrogen oxide (NOx), a significant pollutant known for its contribution to smog formation and its impact on tropospheric ozone and acid rain, is a byproduct of the combustion process. NOx formation becomes particularly pronounced in engines operating at higher loads and elevated temperatures within the cylinder. Notably, the exclusive use of bioethanol tends to reduce NOx emissions due to its lower combustion temperature, as indicated in Table 2. Additionally, bioethanol exhibits a substantially higher latent heat of evaporation, leading to enhanced cooling of the intake air–fuel mixture compared to pure gasoline. This cooling effect results in reduced temperatures in the cylinder during the intake and compression strokes. The combustion temperature also decreases, which directly affects the formation of NOx compounds. Upon replacing pure gasoline (E0) with gasoline–bioethanol blends such as E10, E30, E50, or E70, specific NOx emissions exhibited notable reductions of approximately ~4.5%, ~8.8%, ~18.2%, and ~23.5%, respectively (Figure 10). This significant decrease underscores the potential of bioethanol in mitigating NOx pollutants, thus addressing environmental concerns related to combustion-related emissions. In other studies, where the tests were performed at a constant engine power or torque rather than at constant throttle, opposite results were obtained, i.e., increasing ethanol content also increases NOx formation [17]. In general, there is a noticeable scatter and variation in the data [25,30]. An examination of Stage I of the study reveals that while increasing the throttle opening from 15% to 25% and the engine speed from 2000 rpm to 2500 rpm tends to elevate specific NOx emissions, the addition of bioethanol consistently counteracts this increase, resulting in reduced NOx emissions across all tested conditions.
The results of Stage II of the study demonstrate that advancing the ignition timing leads to a clear increase in specific NOx emissions. This is primarily due to the intensified combustion occurring within a smaller volume and at higher temperatures. However, even in this scenario, the bioethanol additive continues to play a significant role in reducing NOx emissions. Notably, at an ignition timing of approximately Θ ≈ 24° CA bTDC, when the E70 fuel blend reaches its maximum BTE, NOx emissions remain lower compared to E0, even compared to the later ignition case (Θ = 16° CA bTDC). This demonstrates the effectiveness of bioethanol in mitigating NOx emissions, even under conditions that typically promote their increase.
The results of our research suggest potential benefits for the automotive industry and transport policymakers. Increasing the concentration of bioethanol in gasoline significantly improves the environmental performance of the engine. However, challenges persist in optimizing engine parameters for efficiency improvement. Further research is needed to determine optimal blend ratios and engine designs. Collaboration between stakeholders is crucial for scaling up bioethanol production sustainably and addressing distribution challenges.

4. Conclusions

The impact of different bioethanol concentrations (10%, 30%, 50%, and 70%) on gasoline on both the energetic and ecological parameters of an engine operating under stoichiometric air–fuel conditions was analyzed. The research encompassed two stages: Stage I, involving consistent engine speeds (n = 2000 rpm and n = 2500 rpm) and fixed throttle positions (15%, 20%, 25%), and Stage II, focusing on maintaining a fixed engine brake torque of 80 Nm while investigating the impact of different ignition timing settings on engine performance. These results provide useful information for the optimization of engine performance and enhancement of environmental sustainability through the utilization of bioethanol/gasoline blends:
  • When bioethanol concentration in the gasoline blend reaches 70%, the engine’s MB and BMEP increase by approximately 1.7%. This increase comes as a result of a combination of factors such as a ~27.1% reduction in LHV and a ~27.6% increase in fuel mass due to a reduced stoichiometric air-to-fuel ratio. The improved volumetric efficiency of the engine due to lower intake mixture temperatures from bioethanol’s higher latent heat of evaporation also has a positive influence. However, bioethanol’s lower LHV causes a ~26% increase in BSFC_m and a ~22.5% increase in BSFC_V compared to pure gasoline (E0). Increasing the bioethanol concentration to 70%, the BTE increases to 1.7% due to higher combustion efficiency, which also has a positive effect on the increase in torque.
  • The exhaust temperature of E70 decreases by approximately 1.9% due to lower initial combustion temperatures resulting from enhanced intake mixture cooling and a lower flame temperature of bioethanol. While bioethanol has a faster burning rate than gasoline, it goes through a longer ignition delay phase. To achieve maximum BTE and minimum BSFC, the ignition timing for E70 needs to be advanced by around 2° CA compared to the optimal ignition timing for E0.
  • The decrease in specific CO2 emissions when the bioethanol concentration reaches 70% is approximately 1.1%, despite a 24.8% reduction in the fuel’s C/H ratio. However, it is important to note that increased BSFC has a negative impact in this context. Although only a small reduction in specific CO2 emissions is achieved, these greenhouse gases should be considered in conjunction with the fact that bioethanol is a renewable fuel, with E100 having approximately 60% lower CO2 emissions during its life cycle compared to E0.
  • With the introduction of bioethanol, specific NOx emissions decrease due to the lower intake, compression, and combustion temperature, resulting in reductions of approximately 23% when switching from E0 to E70. The oxygen content in bioethanol reduces the emission of incomplete combustion products, resulting in decreases of approximately 17% in specific CO emissions and 43% in specific HC emissions, respectively. Advancing the ignition timing by +2° CA, which optimizes BTE and BSFC but increases specific HC emissions as combustion initiates before the air–fuel mixture is not fully prepared in quality, increases NOx and reduces CO emissions because combustion takes place at a higher pressure and temperature.

Author Contributions

Conceptualization, A.R., G.M. and S.P.; methodology, A.R. and G.M.; software, A.R. and G.M.; formal analysis, A.R. and S.N.; validation, A.R. and S.N.; writing—original draft preparation, A.R. and G.M.; writing—review and editing, S.P. and S.N.; supervision, A.R. and S.P.; project administration, A.R. All authors have read and agreed to the published version of the manuscript.

Funding

This research received no external funding.

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

The data presented in this study are available on request from the corresponding author.

Conflicts of Interest

The authors declare no conflicts of interest.

Abbreviations

A/FAir to fuel ratio
BMEPBrake mean effective pressure
BSFC_mSpecific fuel mass consumption
BSFC_VSpecific fuel volume consumption
bTDCBefore top dead center
BTEBreak thermal efficiency
CCarbon
C/HCarbon-to-hydrogen ratio
CACrank angle
COCarbon monoxide
CO2Carbon dioxide
EEthanol
ECUElectronic control unit
HHydrogen
HCHydrocarbons
LHVLower heating value
MBBrake torque
nEngine speed
NOxNitrogen oxides
OOxygen
SISpark ignition
TexExhaust Temperature
ΘIgnition timing
λ (lambda)Excess air ratio

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Figure 1. Engine test scheme: 1—engine; 2—shaft; 3—engine load stand; 4—load stand data processing module; 5—crankshaft sensor; 6—spark plug; 7—spark timing indicator; 8—air meter; 9—throttle control; 10—fuel mass meter; 11—injector; 12—exhaust temperature sensor; 13—oxygen (lambda) sensor; 14—engine ECU; 15—exhaust gas analyzer.
Figure 1. Engine test scheme: 1—engine; 2—shaft; 3—engine load stand; 4—load stand data processing module; 5—crankshaft sensor; 6—spark plug; 7—spark timing indicator; 8—air meter; 9—throttle control; 10—fuel mass meter; 11—injector; 12—exhaust temperature sensor; 13—oxygen (lambda) sensor; 14—engine ECU; 15—exhaust gas analyzer.
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Figure 2. Dependencies of MB and BMEP on fuel type, throttle opening, and engine speed in Stage I tests.
Figure 2. Dependencies of MB and BMEP on fuel type, throttle opening, and engine speed in Stage I tests.
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Figure 3. Dependencies of BSFC_m on fuel type and: I—throttle opening and engine speed; II—ignition timing.
Figure 3. Dependencies of BSFC_m on fuel type and: I—throttle opening and engine speed; II—ignition timing.
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Figure 4. Dependencies of BSFC_V on fuel type and: I—throttle opening and engine speed; II—ignition timing.
Figure 4. Dependencies of BSFC_V on fuel type and: I—throttle opening and engine speed; II—ignition timing.
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Figure 5. Dependencies of BTE on fuel type and: I—throttle opening and engine speed; II—ignition timing.
Figure 5. Dependencies of BTE on fuel type and: I—throttle opening and engine speed; II—ignition timing.
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Figure 6. Dependencies of Tex on fuel type and: I—throttle opening and engine speed; II—ignition timing.
Figure 6. Dependencies of Tex on fuel type and: I—throttle opening and engine speed; II—ignition timing.
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Figure 7. Dependencies of CO2 on fuel type and: I—throttle opening and engine speed; II—ignition timing.
Figure 7. Dependencies of CO2 on fuel type and: I—throttle opening and engine speed; II—ignition timing.
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Figure 8. Dependencies of CO on fuel type and: I—throttle opening and engine speed; II—ignition timing.
Figure 8. Dependencies of CO on fuel type and: I—throttle opening and engine speed; II—ignition timing.
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Figure 9. Dependencies of HC on fuel type and: I—throttle opening and engine speed; II—ignition timing.
Figure 9. Dependencies of HC on fuel type and: I—throttle opening and engine speed; II—ignition timing.
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Figure 10. Dependencies of NOx on fuel type and: I—throttle opening and engine speed; II—ignition timing.
Figure 10. Dependencies of NOx on fuel type and: I—throttle opening and engine speed; II—ignition timing.
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Table 1. Engine data.
Table 1. Engine data.
Specifications of the Nissan HR 16DE EngineValue
Number of cylinders4
Piston stroke83.6 mm
Cylinder bore78 mm
Number of valves per cylinder4
Displacement1598 cm3
Compression ratio10.7
Nominal power84 kW at 6000 rpm
Maximum engine torque156 Nm at 4400 rpm
Table 2. Fuel properties [35,37,38,39,40,41].
Table 2. Fuel properties [35,37,38,39,40,41].
FuelFuel
Properties Gasoline 100% (E0)Bioethanol 100% (E100)
Chemical formulaCnH2n+2 (C4–C12)C2H5OH
Molecular weight100–10546.07
Elemental composition %:
Carbon (C)86.0052.14
Hydrogen (H)13.99813.13
Oxygen (O)0.00234.73
C/H6.153.97
Density (20 °C), kg/m3736790
Viscosity (40 °C) (mm2/s)0.4–0.81.13
Boiling point, °C27–22578
Latent heat of evaporation, kJ/kg364840
Auto-ignition temperature, °C257422
Laminar flame speed, cm/s5163
Adiabatic flame temperature, °C23072247
Freezing point, °C−40−114
Stoichiometric air to fuel ratio (A/F),
kg air/1 kg fuel		14.849.10
Flammability limits by volume in air, %:
lower limit~0.6~3.5
upper limit~8~15
Octane number88–98109
Lower heating value (mass) (LHV_m), MJ/kg43.527.0
Table 3. Properties of bioethanol and gasoline blends.
Table 3. Properties of bioethanol and gasoline blends.
Fuel BlendE0E10E30E50E70ΔE70, %
Properties
Density, kg/m3736.00741.75753.01763.96774.595.24
C86.0082.3975.3368.4761.80−28.14
H13.99813.9113.7313.5513.38−4.41
O0.0023.7010.9417.9824.821,240,900
C/H6.145.925.495.054.62−24.76
A/F14.8414.2313.0311.8710.74−27.63
LHV_m, MJ/kg43.5041.7438.3034.9631.71−27.10
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Rimkus, A.; Pukalskas, S.; Mejeras, G.; Nagurnas, S. Impact of Bioethanol Concentration in Gasoline on SI Engine Sustainability. Sustainability 2024, 16, 2397. https://doi.org/10.3390/su16062397

AMA Style

Rimkus A, Pukalskas S, Mejeras G, Nagurnas S. Impact of Bioethanol Concentration in Gasoline on SI Engine Sustainability. Sustainability. 2024; 16(6):2397. https://doi.org/10.3390/su16062397

Chicago/Turabian Style

Rimkus, Alfredas, Saugirdas Pukalskas, Gabrielius Mejeras, and Saulius Nagurnas. 2024. "Impact of Bioethanol Concentration in Gasoline on SI Engine Sustainability" Sustainability 16, no. 6: 2397. https://doi.org/10.3390/su16062397

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