Air-fuel Ratio Research Articles

Exploring high-emission driving behaviors of heavy-duty diesel vehicles based on engine principles under different road grade levels

To reveal the outstanding high-emission problems that occur when heavy-duty diesel vehicles (HDDV) pass uphill and downhill, this study proposes a method to depict the nitrogen oxides (NOx) and carbon dioxide (CO2) high-emission driving behaviors caused by slopes from the perspective of engine principles. By calculating emission and grade data of HDDV based on on-board diagnostic (OBD) data and digital elevation model (DEM) data, the 262 short trips including uphill, flat-road and downhill are firstly obtained through the rule-based short trip segmentation method, and the significant correlation between the road grade and emissions of the short trips is verified by Kendall's Tau and K-means clustering. Secondly, by comparing the distribution changes of three speed categories (acceleration state, constant speed state and deceleration state), the differences in HDDV operating states under different grade levels are discussed. Finally, the machine learning models (Random Forest, XGBoost and Elastic Net), are used to develop the NOx and CO2 emission estimation model, identifying high-emission driving behaviors, particularly during uphill driving, which showed the highest proportion of high-emission. Explained by the feature importance and SHapley Additive exPlanations (SHAP) model that large accelerator pedal opening, frequent aggressive acceleration, and high engine load have positive effects both on NOx and CO2 emissions. The difference is in the air-fuel ratio that the engine in the rich or slightly lean burning state will increase CO2 emissions and the lean burning state will increase NOx emissions. In addition, due to the uncertainty of the actual uphill, drivers often undergo a rapid “deceleration-uniform-acceleration” process, which significantly contributes to high NOx and CO2 emissions from the engine perspective. The findings provide insights for designing driving strategies in slope scenarios and offer a novel perspective on depicting driving behaviors.

Determination of cyclic air-fuel ratio and analysis of low and high-frequency variations in dual-fuel RCCI engine

Higher cyclic variations (CVs) in the engine affect the performance, emissions and drivability of the vehicle. Higher CVs are one of the challenges in dual-fuel reactivity-controlled compression ignition (RCCI) engines, mainly at lower loads. Cyclic disparities in the charge preparation, such as air-fuel ratio (AFR), result in CVs in the combustion parameters. The pressure moment method (PMM) is employed in the gasoline/methanol-diesel RCCI engine to estimate cyclic disparities in AFR. The logged cyclic in-cylinder pressure is used to calculate the cyclic AFR. After determining the cyclic AFR, statistical analysis and return maps are applied for the analyses of variations in the AFR, CA10, CA50, pmax and IMEP. For examining the low and high-frequency disparities in cyclic [Formula: see text] and its relationship with CA10, Wavelet transform (WT) is further applied. A good relationship is found between the estimated mean AFR and the experimental mean AFR. Return maps signify that for the earlier start of injection (SOI), the data points of AFR are more scattered correspondingly, the data points for CA10, CA50, pmax and IMEP are more scattered. WT analysis shows that both high-frequency and low-frequency variations are present in dual-fuel RCCI combustion. It is found that high-frequency discrepancies in the AFR are consistent throughout the engine cycles for all the tested injection timings. Wavelet results confirm that high-frequency fluctuations in AFR result in disparities in CA10 and IMEP.

Safety of using hydrogen: Suppression of detonation in hydrogen-air mixtures

Safety of using hydrogen as fuel in aerospace applications is closely connected with hydrogen explosion safety during its transportation and stockpiling at launch places. In this paper, preventing the detonation propagation in the mixtures of hydrogen with air due to accidental hydrogen releases is studied in numerical experiments. Another fuel - hydrocarbon propylene – is studied as an optional inhibitor to be added in a small volume quantity to hydrogen-air mixture. The dependence of detonation wave cellular structure on the content of inhibitor is studied for different fuel-air ratios. The results make it possible determining the content of inhibitor sufficient for preventing the detonation onset or destroying the existing detonation wave.

An experimental study of thermoacoustic instabilities in a RP-3 fueled multi-swirl stabilized lean direct injection combustor

An investigation of self-excited combustion instabilities in a RP-3 fueled, multi-swirl stabilized, lean direct injection (LDI) combustor was performed and investigated with different operating conditions (inlet Reynolds number and fuel–air ratio (FAR)). Pressure fluctuation and heat release data were simultaneously collected using a 3-channel synchronous acquisition system. The results show that as the FAR increases, combustion transitions from a low oscillation mode to a high oscillation mode. During the modal transition, the oscillating flame structure, formed by vortex shedding in the shear layer and the recirculation zone, is then transformed into contraction and expansion movements from the front of the central recirculation zone towards the downstream and radial directions of the combustor. When combustion is in a low oscillation mode, the driving capability of the flame is relatively low. Upon entering a high oscillation mode, the overall driving energy of the flame can maintain combustion in a limit cycle oscillation state.

Comparative Analysis Of Cycle-To-Cycle Variabilities And Combustion Development In An Optical Spark-Ignition Engine Fueled By Pure Hydrogen And Propane: Insights From Chemiluminescence and PI

Hydrogen, derived from renewable sources and devoid of carbon emissions, is a pivotal energy carrier for the future. Representing a viable substitute for fossil fuels in internal combustion engines (ICEs), contemporary studies advocate using very-lean and ultra-lean hydrogen-air mixtures, with a fuel-air equivalence ratio below 0.5, as a potent strategy to reduce NOx emissions in hydrogen-fueled ICEs. An experimental setup with an optical spark-ignition engine was devised to investigate the primary factors influencing cycle-to-cycle variations in H2ICEs by optimizing mixture homogeneity and focusing the study on flame interaction with in-cylinder aerodynamics. Simultaneous in-cylinder pressure, chemiluminescence, and PIV analyses were performed to characterize and compare the behaviors of ultra-lean hydrogen-air and propane-air flames, assessing flame development and cyclic variation features. Results indicate that the flame development of hydrogen and propane is significantly different. Propane exhibited increased in-cylinder pressure trace variability at lean and rich flammability limits with a high flame development difference between fast and slow cycles. In contrast, hydrogen-air mixtures under various equivalence ratios (from very-lean to ultra-lean) presented much more stable in-cylinder pressures. Furthermore, fast propane flames were mainly advected to the cylinder's symmetrical axes, while fast hydrogen flames started further away from the spark plug. Horizontal and vertical PIV measurements showed a single structure flow field over the studied conditions with mainly intensity variations over the measured cycles. Fast flames were associated with more intense tumble motion. The differences between fast and slow flames for hydrogen are attributed to the early flame development. However, after initial differences in flame development over several crank angles, there are similarities in all cycles, suggesting that the low variability in in-cylinder pressures is mostly due to the robustness of hydrogen flame ignition and its independence from in-cylinder flow small variations at the early development phase.

Evaluating Lean Combustion Cycle Stability and Emissions in Spark Ignition Engines with Gasoline, Ethanol, and Methanol Blends

Abstract Fuels for vehicles account for a large portion of the world’s total energy demand, which in turn leads to increased carbon emissions. Ethanol and methanol are a fuel with a simple carbon chain and OH- bonds. It has similar properties to gasoline, and ethanol can be made from the fermentation of plant carbohydrates, called bioethanol. The advantage of using bioethanol is that it contributes to carbon neutrality. This paper will investigate the use of three manually blended gasoline ethanol and methanol (GEM) fuels in a spark ignition engine to address cycle-to-cycle variation (CCV), knock potential, and emissions with lean blend conditions. In the experiments conducted, the air-fuel ratio was conditioned lean by utilizing an electronic control unit to adjust the injector spray duration. This experiment provides results that there is a potential for mild knocking on the use of alcohol fuel with lean fuel mixture conditions at engine speed 4000 RPM, while at engine speed 6000 RPM and 8000 RPM the use of GEM tends to be stable, but in the CCV results the increase in COV (coefficient of variation) value using GEM fuel tends to be more sloping, especially with the addition of more methanol. Emission results from the use of GEM produce top emission CO2 value obtained by the E5M15 mixture at λ=1.2 and an engine speed of 8000 RPM, with a value of 13.75% and then peak CO2 emissions at a value of λ = 1.2 whereas in the use of pure gasoline peak CO2 is at a value of λ = 1.1.

Fuel-air ratio effect on hydrogen-methane flames in a high pressure burner for gas turbines

This numerical simulation studied the effect of H2-CH4 flame equivalence ratio on turbulent premixed combustion at 50%-50% concentration (by volume). The equivalence ratio was varied from 0.45 to 1.0 in 0.5 increments for 126 kW operating power, matching a 3.3 bar inlet reactant pressure. Tests utilized a gas turbine combustor. The thermal field, flow field, and pollutant emissions (NOx and CO) underwent rigorous analysis. The modelling framework applied steady Reynolds-Averaged Navier-Stokes (RANS) equations coupled to a probability density function (PDF) approach for turbulence-chemistry interactions and a NOx formation model. Results showed increasing equivalence ratio from 0.45 to 1.0 elevated temperature approximately 900 K, significantly promoting NOx up to 1600 ppm and CO beyond 1900 ppm. However, equivalence ratio changes minimally impacted the overall flow field, maintaining stabilized flames. These findings provide new insight on thermochemical effects and flame stability in gas turbine (G.T) combustors across a range of equivalence ratios relevant for clean, high-pressure H2-CH4 combustion. The combined RANS-PDF methodology enables predictive simulation of turbulence, kinetics, emissions, and flame stability to guide optimal fuel-air ratio selection and low-emission combustor design.

Experimental study of combustion efficiency and outlet temperature distribution characteristics of a combined evaporative flameholder

In ramjet engines and afterburners, combined stabilizers are employed to achieve effective flame stabilization. This paper designs a combined evaporative flame stabilizer, aimed at enhancing combustion performance and flame propagation under sub-atmospheric conditions. Combustion efficiency and outlet temperature distribution were experimentally studied under varying inlet Mach numbers, temperatures, pressures, and equivalence ratios. Results indicate that combustion efficiency increases with temperature from 600 K to 800 K, initially increases and then decreases with Mach number from 0.11 to 0.19, and decreases with pressure from 0.04 to 0.101 MPa. At an inlet temperature of 600 K, combustion efficiency drops from 55.84 % to 19.36 % as the fuel–air ratio (FAR) increases from 0.008 to 0.044, and then rises to 24.74 % at a FAR of 0.055. Similar outlet temperature distribution characteristics were observed under different inlet conditions. As the Mach number increases, the peak position of the outlet temperature gradually moves from the center to the lower wall. This study provides design guidance and engineering value for improving the combustion performance of flameholders in afterburners or ramjet engine combustion chambers.

Efficiency of Boiler and Steam Turbine for Power Plant Unit 2 PT. XYZ

PT. XYZ has an electric power capacity of 70 MW and began operating in 2014 during its operation there has been a decrease in power from 35 MW at the time of commissioning to 32 MW. This study investigates the impact of the air-fuel ratio (AFR) on the efficiency of a thermal system, focusing on the boiler, turbine, and overall thermal cycle efficiency. Variations in excess O2 in flue gas were examined at levels of 5.0%, 5.5%, and 6.0%. The results reveal that the boiler efficiency peaks at 5.0% excess O2 (73.50%), while an increase in excess O2 or AFR leads to a decrease in efficiency. Turbine efficiency remains relatively stable (74-76%) despite a slight decline with increased AFR. The thermal cycle efficiency reaches its maximum at an AFR of 13.61 (45.60%) but diminishes at higher AFR values.

Experimental investigation of knock control criterion considering power output loss for a PFI SI methanol marine engine

This study presents a new knock control criterion based on different loads and engine power output loss. By utilizing a modified port fuel injection (PFI) spark-ignition (SI) methanol marine engine, the suppressive effects of retarding ignition timing, reducing air-fuel ratio and delaying injection timing on knock intensity at different loads were investigated. Subsequently, a comparative analysis of three knock control strategies was conducted to determine their impacts on power output and thermal efficiency, thus proposing the optimal knock control strategy at different loads. The results show that at both low load (MAP = 73 kPa) and high load (MAP = 139 kPa), the high knock intensity in KLSA (knock-limited spark advance) +5 case is reduced to the safety limitation by retarding ignition timing and reducing air-fuel ratio, while retarding injection timing can effectively suppress knock only at low load. Furthermore, under KLSA+5 condition, there is a significant increase in the probability of severe knock for CA05 earlier than the knock boundary. As the knock tendency is mitigated, IMEP reduces monotonically. There is lower power output loss by optimizing injection timing and air-fuel ratio at low load, and optimizing ignition timing at high load, while the air dilution strategy consistently results in minimal thermal efficiency loss.

Research on air-fuel ratio of rotary engines based on variable universe fuzzy control

Abstract A study on the air-fuel ratio control system for the Wankel rotary engine was conducted, where the overall model of the engine was developed in MATLAB/Simulink based on the mean value model. The variable universe fuzzy integral composite control algorithm was applied to feedback control, and the construction and simulation of the control algorithm were completed in MATLAB/Simulink. The results indicate that compared to PID control, variable universe fuzzy control reduced the engine’s fuel injection error by 60.37% and 35.7% under steady-state and transient conditions, respectively. This demonstrates the favorable control effectiveness of variable universe fuzzy control in rotary engines, providing insights and methods for future research on rotary engine control systems.

Cyclic coupling and working characteristics analysis of a novel combined cycle engine concept for aviation applications

The imperative for small aviation engines lies in the pursuit of heightened power-to-weight ratios and thermal efficiencies. Relying solely on piston engines and gas turbines is insufficient to concurrently meet these evolving performance demands. This paper introduces the concept of a combined cycle aviation engine (CCAE), amalgamating the cycle modes of piston engines and gas turbines. The CCAE achieves flexible control over turbine operating states and engine performance through the adjustment of the energy distribution between these two cycles. The air diversion strategy (α) and the burner's fuel supply strategy (λb) are identified as the key determinants of system performance. To comprehensively investigate the impact of α and λb on CCAE's performance, this paper constructs a theoretical model, a simulation model, and a test bench. The simulation model's accuracy is validated through test data, and the air-fuel ratio range for burner stable combustion is explored. The simulation results indicate a reduction of 50 % in the fluctuation of turbine speed within a single cycle. Under high-altitude conditions, CCAE's intake mass flow rate, power, and efficiency are notably enhanced when compared to conventional turbocharged piston engines. These findings contribute valuable insights that can inform the application of CCAE within the aviation domain.

Experimental investigation of the effect of air/fuel ratio change on JP8 swirl flame characteristics with image processing methods

In this study, the stable combustion ranges and emission values of JP8 fuel, which is used in military aviation, were tested and optimum conditions were determined. The AFR (Air/Fuel Ratio) of the JP8 flame was increased experimentally at constant thermal power in a gas turbine combustion chamber. In the study, AFR were tested as 30/1, 33/1, 36/1, 39/1 and 42/1. A generator with 0.4 swirl number is placed at the burner outlet. Under these conditions, the effect of external acoustic enforcement frequencies on dynamic instabilities at different AFR was investigated. Flame length and thickness data were extracted from the images obtained from the image processing technique. The effect of AFR change on the combustion chamber temperature was examined and pollutant emissions were measured. The results showed that the most stable flame appeared in AFR 33/1 case at 155 and 300 Hz resonance frequencies under acoustic enforcements. Additionally, when the AFR was increased to 42/1, flame instability increased at all frequency values. Moreover, it has been determined that the most optimum mixture in terms of combustion chamber exit temperature and CO emissions is AFR 33/1. There was an increase in NOX emissions by up to 39/1 with the increase in AFR.

Hydrogen doping control method for gasoline engine acceleration transient air-fuel ratio

One of the primary contributors to automobile exhaust pollution is the significant deviation between the actual and theoretical air-fuel ratios during transient conditions, leading to a decrease in the conversion efficiency of three-way catalytic converters. Therefore, it becomes imperative to enhance fuel economy, reduce pollutant emissions, and improve the accuracy of transient control over air-fuel ratio (AFR) in order to mitigate automobile exhaust pollution. In this study, we propose a Linear Active Disturbance Rejection Control (LADRC) Hydrogen Doping Compensation Controller (HDC) to achieve precise control over the acceleration transient AFR of gasoline engines. By analyzing the dynamic effects of oil film and its impact on AFR, we establish a dynamic effect model for oil film and utilize hydrogen's exceptional auxiliary combustion characteristics as compensation for fuel loss. Comparative experimental results demonstrate that our proposed algorithm can rapidly regulate the AFR close to its ideal value under three different transient conditions while exhibiting superior anti-interference capability and effectively enhancing fuel economy.

Working process model development of the gas turbine engine combustor fueling on methanol

The use of methanol as a fuel for aircraft and stationary gas turbine engines (GTE) is a priority direction in engine building. It is well known that when modeling the GTE performances using first-level mathematical models, there is an error in calculating specific fuel consumption, which is caused by the simplified description of the GTE combustor working process. The object of the study is the working process in the GTE combustor fueling on methanol. The peculiarity of the developed mathematical model of the working process of the GTE combustor is the use of enthalpy dependencies on temperature, pressure, and mixture composition. Enthalpy dependencies in this form implicitly account for the effect of thermal dissociation and allow for the correct formulation of the equivalent combustion reaction path. For two components (H2O and CO2), accounting for pressure leads to the fact that at standard temperature and partial pressures exceeding the saturation pressure, these components exist in a liquid state. This situation, with a constant enthalpy increment in the equivalent process of heating the combustion products from the standard temperature to the temperature at the end of adiabatic heat supply, decreases this temperature. Clarification of the temperature at the combustor outlet leads to changes in all calculated combustor performances, including the combustor fuel air ratio. The calculation results of the fuel air ratio are compared with known experimental data of the General Electric CF6-80A engine combustor (USA). The average calculation error of the fuel air ratio does not exceed 4 %. The developed model can be implemented in existing and developing mathematical models of gas turbine engines for temperatures at the end of the combustion process below 2,600 K

Determination of Air–Fuel Ratio at 1 kHz via Mid-Infrared Laser Absorption and Fast Flame Ionization Detector Measurements in Engine-Out Vehicle Exhaust

<div>Measurements of air–fuel ratio (AFR) and <i>λ</i> (AFR<sub>actual</sub>/AFR<sub>stoich</sub>) are crucial for understanding internal combustion engine (ICE) performance. However, current <i>λ</i> sensors suffer from long light-off times (on the order of seconds following a cold start) and limited time resolution. In this study, a four-color mid-infrared laser absorption spectroscopy (LAS) sensor was developed to provide 5 kHz measurements of temperature, CO, CO<sub>2</sub>, and NO in engine-out exhaust. This LAS sensor was then combined with 1 kHz hydrocarbon (HC) measurements from a flame ionization detector (FID), and the Spindt exhaust gas analysis method to provide 1 kHz measurements of <i>λ</i>. To the authors’ knowledge, this is the first time-resolved measurement of <i>λ</i> during engine cold starts using the full Spindt method. Three tests with various engine AFR calibrations were conducted and analyzed: (1) 10% lean, (2) stoichiometric, and (3) 10% rich. The measurements were acquired in the exhaust of a light-duty truck with an 8-cylinder gasoline engine. The LAS-FID-based <i>λ</i> sensor results were compared with those obtained from a universal exhaust gas oxygen (UEGO) sensor. The LAS-FID method provided robust <i>λ</i> measurements from the first combustion exhaust event (avoiding the light-off time associated with traditional <i>λ</i> sensors) in addition to enhanced temporal resolution (on the order of 100× increase compared to traditional diffusion-based <i>λ</i> sensors). The insight gained from this novel method could be used to benefit crank, cold start, and open- or closed-loop air–fuel ratio control strategies in gasoline engines for reduced emissions.</div>

Investigating Knocking Potential, Cycle Stability, and Emission Characteristics in Lean Spark Ignition Engine with Gasoline, Ethanol, and Methanol

In this paper, an investigation of the use of gasoline-ethanol-methanol on the spark ignition engine is presented, it is not common practice on public roads to use three fuels simultaneously in a spark-ignition engine. Using methanol reduces the ignition delay during combustion, especially at lean air-fuel ratios, and reduces knocking potential in small amounts. The best result ignition delay with value λ= 1,3 obtained in the E5M15 mixture with SoC occurred at 325 CAo, while the value λ= 1,0 also obtained on the same mixture with SoC occurred at 321,5 CAo. The CCV results indicate a more sloping increase in the COV (coefficient of variation) value when using GEM fuel, particularly with the addition of more methanol. The addition of methanol enhances combustion progression and improves the ability of the fuel blend to sustain combustion under lean conditions. Regarding the torque and power values, at λ= 1,0; 1,1; 1,2 are not significantly different, while the value λ= 1,3 is below the other λ values.

Performance and Emission Measurement of Spark Ignition Engines Operating with 100% Methanol Fuel

A small two-wheeler engine and a large, multi-cylinder bus engine are demonstrated for 100% methanol operation and, performance and emissions with methanol are compared to baseline. This kind of study on both small and large engines operating with 100% methanol is not reported in the literature as per the authors’ knowledge. A high flow injector is incorporated for the small engine for methanol. The fuel-air ratio is adjusted to operate the engine around a Lambda value of 1, and ignition timing is optimized to achieve maximum torque. Finer adjustments to Lambda are performed to maintain the nitrogen oxides emission less than that of the gasoline engine. The torque at wide-open throttle is higher than that of gasoline, around 5% higher brake thermal efficiency, and lower or similar regulated emissions are observed with methanol. For the large engine, a liquid nozzle and an electric fuel-pump are incorporated for methanol. Lambda is maintained around 1, and ignition timing is optimized for maximum brake torque while avoiding knocking. The rated torque and power are achieved with around 50% throttle opening, 3% higher brake-thermal efficiency, and lower nitrogen oxides are observed with methanol.

Optimal proportional-integral speed control for closed-loop engine timing system

In internal combustion engines, adjusting the air-fuel ratio is essential to control the speed and minimize the burnt fuel. The throttle opening is the actuator to control the air-fuel. A better design for the used/conventional controller can give a better response without additional cost. In this work, the proposed controller gains of the proportional-integral (PI) controller are tuned to enhance the speed in constant and variable drive cycle modes. The tuning process is conducted based on two of the most efficient performance indices used in this field. The performance indices are integral absolute error (IAE) and integral time absolute error (ITAE). The optimization problem is solved using three reliable stochastic optimization algorithms to ensure mature convergence of the solutions, to avoid local optima solutions, and to ensure effective shrinking of the search space. The optimization algorithms are teaching-learning-based optimization (TLBO), particle swarm optimization (PSO), and genetic algorithm (GA). Different simulations are conducted to validate the results. The results are compared with conventional tuning methods regarding the system's time response.

Optimasi AFR pada Gasoline Engine Menggunakan Sistem Controller pada Vehicle Speed Censor

The number of motorised vehicles has increased significantly in recent times. Derived petroleum products are still the main fuel for these internal combustion engines. But on the other hand, its availability is decreasing and its price is becoming increasingly expensive. This problem is the background to the importance of efforts to improve the efficiency of fuel consumption in motorised vehicles. One way to improve fuel efficiency is by increasing the optimisation of Air Fuel Ratio (AFR) with a control system. In this research, the control system used is an external engine control system (Honda Verza 150 FI) that works based on vehicle speed data. This control system works by resetting the fuel supply released when the motorbike decelerates so as to produce a better AFR value and more efficient fuel consumption. Based on the results of experimental tests conducted at 5 different deceleration speed variations (40 km/h, 50 km/h, 60 km/h, and 70 km/h) when using a modified ECU there is an increase in AFR value when compared to when using a standard ECU. The highest increase in AFR value occurs at a deceleration speed of 70 km/h with the AFR difference reaching 0.4 when compared to using the standard ECU. As for fuel consumption, the modified ECU is 150 cc more efficient than the standard ECU with the same test distance of 35.2 km