The Recent Advancements in Gasoline technology: Innovations in Fuel Formulation, Engine Design, and Emission Control

The recent developments in gasoline and spark ignition (SI) engine technologies have been critical to meeting the increasing demand for cleaner and more efficient transportation systems. Downsizing of SI engines, as part of enhancing fuel efficiency, improving performance, and reducing emissions, has emerged with the increasing emphasis on hybridization and electrification. This study focuses on alcohol-gasoline blends and fuel additives, proving their potential to enhance torque and brake power while balancing emissions. The study also shows that forced induction technologies, especially turbocharging, effectively ensure appropriate power output and fuel consumption in downsized engines. Forms of engine design, such as swirl control valves and advanced injection timing, further enhance performance and combustion efficiency. Although progress has been made, challenges remain, particularly with the trade-offs among performance, fuel economy, and emissions. This paper synthesizes the findings of some recent studies that assess the practical implications of such advances and point to areas that require further investigation to exploit their potential fully. The conclusions emphasize how downsized SI engines in hybrid and electrified powertrains represent a stepping stone toward a cleaner, more sustainable future of transportation.

Introduction:

According to the IEA’s World Energy Outlook 2023, clean energy and technologies will become more significant by 2030. This prediction includes almost 10 times the number of Electric Vehicles (EVs) seen worldwide.1 To meet those expectations, the industry has seen a pivot in funding and research toward hybridization and electrification. Consequently, innovations in spark ignition engine design and fuel optimization now aim to complement hybrid systems by downsizing, enhancing fuel efficiency, and reducing emissions.
Engine downsizing is the practice of reducing the physical size and displacement of an SI engine while maintaining performance and increasing efficiency. This reduction is usually done by reducing the number of cylinders in the engine; in hybrid vehicles, downsized SI engines work alongside electric motors, compensating for any power loss due to downsizing. This paper will focus on the latest research into designs that significantly impact engine downsizing, such as fuel formulation enhancements, forced induction, and optimization of engine parts.

Fuel Formulation:

Downsized SI engines are designed to be smaller yet more efficient. In hybridization electrification, SI engines operate under specific conditions (typically loading). This requires fuel that’s designed to deliver enough power while maintaining low risk of engine damage. Thus, gasoline needed to be improved by additives, one of which is Alcohol-gasoline blends. Alcohols like ethanol and methanol have high octane ratings, improving fuel resistance to knocking. The following summaries are of two different studies focused on alcohol-gasoline blends.
• Alcohol-Gasoline
In 2021, Ijaz Malik et al. conducted a comparative study between a Methanolgasoline blend (12% methanol, M12) and gasoline on a 163cc SI engine at varying engine speeds and loads. The torque was produced by the engine was inspected under stoichiometric air-fuel mixture conditions as well as SAE J1349 standard to ensure optimal combustion characteristics. The stoichiometric air-fuel ratios for gasoline and methanol were 14.7:1 and 6.5:1 (kg/kg) respectively. The results revealed that torque for M12 at 20psi and 40 psi load was 7.28% and 7.01% higher than gasoline, respectively (Figure 1a). The results also show an average torque increase of 26% at 40psi in comparison to 20psi (Figure 1b). This behavior is primarily due to the effect of load increase on torque, where an increase of load causing an increase in combustion energy generated. M12 produces higher torque in comparison to gasoline because of methanol’s properties allowing for more efficient combustion and antiknock capabilities. This increase could also be seen in engine brake power, where M12 produced 6.69% more brake power than gasoline at 20psi and 6.41% more at 40psi (Figure 2a). A similar average increase in brake power of 24.37% is revealed at 40psi than at 20psi (Figure 2b). These findings highlight the capabilities of M12 contra to gasoline in terms of performance and speed.2
The study explores four gas emissions from the engine: CO, CO2, HC, and NOx. The CO and HC emissions for M12 were 9.77% and 6.31% lower than gasoline at higher loads. However, CO2 and NOx emissions were 2.80% and 27.58% higher for M12 than for gasoline. The increase in NOx emission is related to the engine cylinder’s high combustion temperatures and oxygen availability. These results highlight the trade-off between emission reduction and fuel performance.2

• Alcohol-Additive-Gasoline
Further advancing in the line of inquiry, in 2022, Yakin et al. examined an pure gasoline, alcohol-gasoline blend E5 (95% gasoline 5% ethanol by volume), M5 (95% gasoline 5% methanol by volume), and a NaBH4-alcohol-gasoline blend ES5 (95% gasoline, 5% NaBH4 solution dissolved in 5% ethanol by volume), MS5 (95% gasoline, 5% NaBH4 solution dissolved in 5% methanol by volume) on a single-cylinder SI engine. They found that the torque of E5, M5, and MS5 are all higher than gasoline, while the ES5 was lower (Figure 3). ES5 being lower than gasoline could be interpreted as due to many factors, such as the negative effects of NaBH4 in the blend and the low
calorific value of the ES5 fuel. As expected, all engines’ average consumption rate is higher than gasoline’s. This increase in the specific fuel consumption, measured by mass, of E5, M5, ES5, and MS5 is 2.33%, 2.41%, 0.96%, and 1.78%, respectively
(Figure 4). This is caused by the alcohol and NaBH4 having a lower heating value, and a higher density than pure gasoline causing the engine to burn more to get to the same amount of power.3
The emissions calculated by the experiment also showed promising results. The main emissions the study focused on were CO, CO2, HC, and NOx. CO emissions were reduced in the fuel blends compared to gasoline due to the improved hydrogen combustion in NaBH4. NOx emissions were decreased in the fuel blends in comparison to gasoline due to the lower exhaust temperature, which is the product of the alcohol’s high latent heat of evaporation, as well as the faster flame propagation speed, which leads to shorter combustion time, reducing the period at which the cylinder is at high temperatures thus decreasing NOx emissions. The highest emission of CO and NOx is by gasoline, and the lowest is by ES5 for CO and MS5 for NOx. The same cannot be said about CO2 emissions that increased compared to gasoline for E5, ES5, M5, and MS5 by 8.51%, 34.48%, 30.46%, and 25.95%, respectively. HC emissions showed mixed results where ethanol blended fuels (E5, ES5) decreased compared to gasoline, while methanol blended fuels (M5, MS5) increased. This could be attributed to poor air-fuel mixture and different heating values of the fuels.3

Forced Induction:

Forced induction encompasses technologies such as turbocharging and supercharging, which increase an engine’s power output by increasing the mass of air getting into the combustion chamber. This allows more fuel to be burned, enhancing performance without increasing the engine size.
Figure 3: Torque for the different fuels at varying engine speeds

• Turbocharging
In 2023, Silva et al. conducted a numerical study to analyze the effects of engine downsizing and turbocharging on performance and emissions using a 1.6L E.torQ turbocharged engine as the base model. The study involved creatingsimulations with reduced displacements of 1.4L, 1.2L, and 1.0L engines and comparing them with the base model and a naturally aspirated 1.6L engine at full load. The results showed that the 1.2L turbocharged engine achieved higher power and torque than the naturally aspirated engine across most speeds (Figure 5). At 3000 rpm, all engines achieve their lowest brake-specific fuel consumption (BSFC) value. Meaning all engines at 3000 rpm operate at their most efficient point. The 1.2L turbocharged engine was found to be the best overall, achieving a good compromise between displacement and turbocharge efficiency, minimizing fuel consumption at higher and lower speeds.4
The analysis revealed that while CO2 emissions decreased at high speeds with reduced displacement, NOx emissions increased, particularly at higher engine speed, due to elevated cylinder temperatures. Conversely, CO emissions declined at higher speeds, suggesting improved combustion. These findings underscore the potential of downsizing combined with turbocharging to enhance engine efficiency and reduce specific emissions under optimal operating conditions.4

Engine Design:

Engine design is crucial for optimizing SI engines. This optimization includes improving efficiency, performance, and lower emissions. The following studies will focus on the swirl control valve, injection time, and injection pressure.

•   Swirl Control Valve (SCV)
A study by Shin et al. focused on the effects of a swirl control valve (SCV) on the flow and mixture preparation in a high compression ratio in a direct injection (DI) engine. The researchers have analyzed the effects of the alteration of the SCV angle (Figure 6) on the flow characteristics. The SCV angle affects the flow characteristics such that a smaller SCV angle (closer to 0 degrees) results in a higher swirl ratio, it’s rotating alongside the cylinder walls, while a higher SCV angle (closer to 45 degrees) results in a higher turbulence ratio hence its up-down motion along the vertical plane of the cylinder. A SCV angle higher than 45 degrees was found to have insignificant effects on the flow intensity (Figure 7). The results showed that the SCV angle optimizes performance depending on the operating conditions. An angle closer to 0 degrees was best for lean-burn performance, stratification, and fuel economy, while an SCV angle closer to 45 degrees is best for homogeneous combustion, turbulence, and high-load efficiency. Lastly, an SCV angle beyond 45 degrees diminished performance improvements compared to (0 degrees – 45 degrees).5

•   Injection Time
Wang et al. in 2024, investigated the influence of injection timing on mixture formation, combustion, and emission characteristics in a turbocharged n-butanol direct injection spark ignition (DISI) engine. They conducted a numerical simulation focused on injection timings ranging from -320 °CA to -260 °CA. They found that early injections (e.g., -320 °CA) lead to inhomogeneous mixtures and increased wall film, whereas delayed injections (e.g., -260 °CA) enhance turbulence and mixture quality, but may lead to more NOx emissions. The reason for this discrepancy is because when injections occur too early, the spray plumes interact with the intake air, reducing the tumble intensity (Figure 8). This diminishes the mixing energy, leading to slower diffusion of the fuel into the air leading to an inhomogeneous mixture. Additionally, when fuel is injected early, the likelihood of fuel droplets hitting the walls of the injector and the cylinder increases due to proximity. This wall film contributes to incomplete evaporation leading to inefficient combustion and higher HC emissions.
While in delayed injections, the injection better aligns with the tumble motion of the air that’s generated by the intake stroke. This shorter time frame allows fuel to remain within the in-cylinder airflow, minimizing wall film and improving homogeneity. Based on those limitations, the study concluded that the optimal injection time is -300 °CA, which offers an ideal compromise between turbulence and mixture homogeneity, and combustion efficiency and emissions control.6
Figure 8: Crank Angle Vs. Tumble Ratio.
Adapted from Wang et al. Effects of injection timing on mixture formation, combustion, and emission characteristics in a N-butanol direct injection spark ignition engine. (2024).
•   Injection Pressure
Xiang Li aMainly, droplet velocity (Normal Component (VN), being the velocity of the droplets alongside the spray axis, and the Tangential Component (VT), being the velocity of the droplets perpendicular to the spray axis), Droplet size (Sauter Mean Diameter (SMD) the measure of average droplet size, weighted by volume and surface area), and spray stability and breakup (Breakup determines how effective the spray is atomized into smaller droplets). The experiment was conducted using a five-hole GDI injector operating at 5.5, 10, 14, and 18 MPa
(Figure 9). The results revealed that droplet velocity increased with higher injection pressures. The VN for 5.5 MPa and 18 MPa being 30 m/s and 42.5 m/s respectively, which is an increase of nearly 42.67%. VT also showed significant improvements, for instance at point (16, 50), VT increases by around 30% from 5.5 MPa to 18 MPa. These findings are significant, because for VN, higher pressures increase the initial kinetic energy, enhancing spray penetration and diffusion rate, and larger values for VT at higher pressures indicate better spray dispersion. The results also showed that the droplet size, measured using SMD, decreased substantially as the pressure increased.
With the increase of pressure from 5.5 MPa to 18 MPa, the droplet size drops from 10 micro meter to 6 micro meters. This represents a reduction of nearly 70%. Regarding stability and breakup, higher pressures indicated a higher probability of aggressive breakup. This shift resulted in a finer spray and a better air-fuel mixture homogeneity.7
Figure 9: Injector five holes, front view and side view.
Adapted from Xiang Li X et al. Optimizing microscopic spray characteristics and particle emissions in a dual-injection spark ignition (SI) engine by changing GDI injection pressure. (2024).

Conclusion:

Advancements in fuel formulations, engine design, and downsizing strategies have emerged as key enablers for the hybridization and electrification of SI engines.
Optimizing engine downsizing has proven to be a good step towards enhancing performance, improving fuel efficiency, and reducing emissions. The review provides critical insights into the multi-dimensional strategy involved in optimizing downsized engines, fuel formulation, forced induction, and improvements in engine design.
While these technologies are promising so much, they also demonstrate some key challenges that must be overcome. Performance, economy, and emissions tradeoffs are particularly critical for hybrid applications. New and emerging fuels and additives must be further developed to achieve full environmental benefit. Forced induction and state-of-the-art injection systems also require further investigation into methods of reducing NOx emissions without affecting performance Therefore, developing and introducing such novelties in downsized SI engines represent an essential passage for a much cleaner and more efficient transport mode.
This challenge, though, from the discussion, evidenced further studies to reach full benefits, which means all the reachable with the given upsizing in a hybrid or electrified architecture.

References:

[1]. IEA. The Energy World is set to change significantly by 2030, based on today’s policy settings alone - news. IEA. https://www.iea.org/news/the-energy-world-is-setto- change-significantly-by-2030-based-on-today-s-policy-settings-alone.
[2]. Ijaz Malik, M. A., Usman, M., Hayat, N., Zubair, S. W. H., Bashir, R., & Ahmed, E. (2021). Experimental evaluation of methanol-gasoline fuel blend on performance, emissions and lubricant oil deterioration in SI engine. Advances in Mechanical Engineering, 13(6), 16878140211025213.
[3]. Yakın, A., Behcet, R., Solmaz, H., & Halis, S. (2022). Testing sodium borohydride as a fuel additive in internal combustion gasoline engine. Energy (Oxford), 254, 124300-. https://doi.org/10.1016/j.energy.2022.124300.
[4]. Silva, L. S., Silva, J. A., Henríquez, J. R., & de Lira Junior, J. C. (2023). Numerical Analysis of Effects of Engine Downsizing and Turbocharging on the Parameters of Performance and Emissions of an Internal Combustion Engine. Arabian Journal for Science and Engineering, 48(3), 2795-2805.
[5]. Shin, J., Kim, D., Son, Y., & Park, S. (2022). Effects of swirl enhancement on incylinder flow and mixture characteristics in a high-compression-ratio, spray-guided, gasoline direct injection engine. Case Studies in Thermal Engineering, 34, 101937- https://doi.org/10.1016/j.csite.2022.101937.
[6]. Wang, X., Zhen, X., He, B.-Q., Awad, O. I., Venugopal, T., Tian, Z., Costa, M., Wang, C., Kale, R., Breda, S., Jiang, C., Duan, Q., Park, C., Zhao, F., … Aleiferis, P. G. (2024, March 20). Effects of injection timing on mixture formation, combustion, and emission characteristics in a N-butanol direct injection spark ignition engine. Energy. https://www.sciencedirect.com/science/article/pii/S0360544224008314
[7]. Xiang Li X, Li D, Pei Y, Peng Z. Optimising microscopic spray characteristics and particle emissions in a dual-injection spark ignition (SI) engine by changing GDI injection pressure. International Journal of Engine Research. 2023;24(4):1290-1299. doi:10.1177/14680874221082793

About the Authors

Dr. Raj Shah is a Director at Koehler Instrument Company in New York, where he has worked for the last 25 plus years. He is an elected Fellow by his peers at IChemE, AOCS, CMI, STLE, AIC, NLGI, INSTMC, Institute of Physics, The Energy Institute and The Royal Society of Chemistry. An ASTM Eagle award recipient, Dr. Shah recently coedited the bestseller, “Fuels and Lubricants handbook”, details of which are available at ASTM’s LongAwaited Fuels and Lubricants Handbook 2nd Edition Now Available https://bit.ly/3u2e6GY.
He earned his doctorate in Chemical Engineering from The Pennsylvania State University and is a Fellow from The Chartered Management Institute, London. Dr. Shah is also a Chartered Scientist with the Science Council, a Chartered Petroleum Engineer with the Energy Institute and a Chartered Engineer with the Engineering council, UK. Dr. Shah was recently granted the honourific of “Eminent engineer” with Tau beta Pi, the largest engineering society in the USA. He is on the Advisory board of directors at Farmingdale university (Mechanical Technology), Auburn Univ (Tribology), SUNY, Farmingdale, (Engineering Management) and State university of NY, Stony Brook ( Chemical engineering/ Material Science and engineering). An Adjunct
Professor at the State University of New York, Stony Brook, in the Department of Material Science and Chemical engineering, Raj also has over 680 publications and has been active in the energy industry for over 3 decades. More information on Raj can be found at https://bit.ly/3QvfaLX
Contact: rshah@koehlerinstrument.com
Dr. Vikram Mittal, PhD is an Associate Professor in the Department of Systems Engineering at the United States Military Academy.  His research interests include energy modeling, technology forecasting, and Alternative fuels. Previously, he was a senior mechanical engineer at the Charles Stark Draper Laboratory.  He holds a PhD in Mechanical Engineering from MIT, an MS in Engineering Sciences from Oxford, and a BS in Aeronautics from Caltech. Dr. Mittal is also a combat veteran and a major in the U.S. Army Reserve.
Ms. Joud Altalag is part of a thriving internship program at Koehler Instrument company in Holtsville, and is a student of Chemical Engineering at Stony Brook University, Long Island, NY where Dr.’s Shah and Mittal are on the external advisory board of directors