Antiknock Performance Research Articles

Experimental and numerical investigation of arch concrete slabs subjected to underwater contact explosions with the inner arch side facing air

Arch structures with their inner arch side exposed to air and outer arch side exposed to water are often encountered in practical projects, and these engineering structures may be subjected to various explosive attacks during operation. This paper investigates the damage mechanism and dynamic response of arch concrete slabs with the inner arch side facing air against underwater contact explosions (UWCEs). The explosion tests of the arch concrete slab with the inner arch side facing air were carried out. The accuracy and applicability of the numerical model were verified by comparing with the explosion results. After that, the failure evolution and energy transition of the arch concrete slab with the inner arch side facing air were studied. The effects of different explosion masses, explosion distances, and reinforcement schemes on the antiknock performance of arch concrete slabs are further explored. The results show that as the explosive mass of UWCEs increases, the damage mode of the arch concrete slab with the inner arch side facing air changes from cracking along the longitudinal direction and local failure to spalling on the inner arch side and fragmentation of the contact specimens. The existence of curvature of the arch slab will cause the damage of the arch slab to intensify. The failure mode of the arch concrete slab changes from local failure to slight failure with cracks as the explosion distance increases. Increasing the longitudinal steel bars on the outer arch side can effectively inhibit the generation and development of cracks.

Collaborative effects of fuel properties and EGR on the efficiency improvement and load boundary extension of a medium-duty engine

EGR dilution combustion has problems such as weakened anti-knock capability at high load, slow combustion speed and poor combustion stability, which results in limitations in the thermal efficiency improvement and load boundary extension of medium-duty highly-downsized engines. It is necessary to combine EGR dilution and other measures to collaboratively control the in-cylinder thermodynamic state and combustion process. The experimental investigations in this study isolate the effect of the ethanol blending ratio in ethanol gasoline on the anti-knock performance, combustion performance and thermal efficiency, and verifies the potential of collaborative optimization of fuel properties and EGR in improving the thermal efficiency and extending the load boundary for a medium-duty highly-downsized engine. The results show that as the load increases, the improvement effect of increasing the blending ratio of ethanol in the anti-knock performance, combustion speed, and the turbine inlet temperature reduction will become more obvious. At high load, using E20 fuel can improve the EGR tolerance, advance the spark timing and CA50, and thus increase the BTE. As the speed decreases, the thermal efficiency improvement effect of E20 fuel gradually increases, and the improved load range extends. The collaborative optimization of E20 fuel and EGR can further extend the high thermal efficiency area of the engine. And the Max. achievable load is 0.11 MPa higher than that of E10, which effectively extends the upper load limit during the stoichiometric combustion.

Analysis of damage characteristics of the rectangular steel container under near-earth explosion loading

In this study, the dynamic response of a semi-buried steel vessel under a near-surface explosion shock load was investigated through full-scale model tests. A three-dimensional precise numerical simulation model of the semi-buried steel vessel structure was established, and the dynamic response and damage consequences under different load conditions were analyzed. The influence of the thickness of corrugated steel on the dynamic damage and antiknock properties of the structure was studied. The results show that the weak part of the rectangular steel vessel structure is mainly located at the connection between the blast-facing panel and the beam column under near-surface explosion conditions. The peak stress and displacement of the blasting surface decrease with the increase in the horizontal angle of the incident wave, whilst/while increase with the height of the explosion. Under the same explosive yield, the main failure mode of the structure is the tearing of the plate and beam under plastic deformation. Increasing the thickness of the corrugated steel can significantly restrain the plastic deformation and acceleration of the plate. When the thickness is increased from 2 mm to 6 mm, the antiknock performance is significantly improved. However, when the thickness is increased from 6 mm to 8 mm, the improvement in antiknock performance slows down. Increasing the height of the enclosing soil can also effectively improve the explosion-proof performance of the structure, with full burial providing the best effect. The research results provide a theoretical basis for the application of rectangular steel vessel structures in the field of protection engineering.

Process comparison and performance evaluation of different entrainers for pressure swing extractive distillation refining gasoline additives based on multi-objective optimization and process intensification

As a new gasoline additive, methyl tertiary amyl ether (TAME) can improve the antiknock performance and quality of gasoline. This study uses an energy-saving process for separating TAME/methanol (MeOH)/H2O by pressure-swing extractive distillation with different entrainers based on multi-objective optimization and 4E analysis. The 1entrainers are screened by the difference in relative volatility of components under different entrainer conditions, and the electrostatic potential of the molecular surface of the system and entrainers are analyzed. Multi-objective optimization of the pressure swing extractive distillation process with 5 different entrainers is carried out based on the generation non-dominated sorting genetic algorithm (NSGA-Ⅱ) optimization scheme, and the Pareto frontier is optimized by the minimum distance method. The results indicate that the extraction schemes of 1,3-propanediol (PDO) and dimethyl sulfoxide (DMSO) have excellent economic and environmental benefits through comprehensive analysis. As an effective means of process intensification, the application of heat pump technology can further reduce process costs and environmental pollution. The coefficient of heating performance (COP) is used to find the most suitable pairing route for heat pump-assisted processes, achieving the goal of reducing gas emissions and energy use. Then, different processes are evaluated in terms of economy, energy consumption, environment, and exergy loss. The results show that the process intensification scheme based on heat pump technology can effectively improve the economic and environmental benefits of the process, reducing the annual total cost (TAC) and gas emissions by 9.19% and 23.55%, respectively. This study provides the selection and reference for azeotrope separation of TAME and recycling of wastewater.

Efficient synthesis of the di‑tert‑butyl peroxide by isobutane selective peroxidation with molecular oxygen over sulfated titanium oxide

Di‑tert‑butyl peroxide (DTBP), an important substance in chemical production, is widely used in olefin polymerization and the improving anti-knock performance of diesel. DTBP synthesized from isobutane selective peroxidation can not only improve the utilization of isobutane resources but also overcome the defects in conventional DTBP synthesis methods. In this work, sulfated TiO2 (STiO2) was developed to catalyze isobutane selective peroxidation to DTBP for the first time. The results demonstrated that high oxygen conversion (>90 %) and DTBP selectivity (>31 wt%) were obtained under the optimal reaction condition. Furthermore, after excluding the effect of mass transfer by designing the experiment and calculation, it is concluded that the reaction activity is related to the total amount of acid site and oxygen adsorption capacity, and the DTBP selectivity depended on the amount of surface S=O site. With the basis that the adsorption state of the intermediate product (tert‑butyl hydroperoxide) on the surface S=O site is ensured by in-situ FT-IR characterization and DFT calculation, the reaction mechanism is proposed. It is worth noting that the performance of the STiO2 catalyst is significantly better than our previously reported MoO3 catalyst. This improvement can be attributed to the lower reaction activation energy and, most importantly, the larger amount of the strong acid site originating from the S=O site. This work provides a class of efficient STiO2 catalysts for DTBP production and the improvement of isobutane utilization.

The interaction of charge motion and EGR on anti-knock performance and efficiency of a medium-duty gasoline engine: An experimental study

Due to the common operating characteristics of medium duty (MD) gasoline engines, achieving higher load at the expense of fuel efficiency is not an acceptable tradeoff. EGR dilution-stoichiometric combustion can suppress the knocking and improve the thermal efficiency, but has problems such as slow combustion rate and poor combustion stability, which have limitations in optimizing combustion for MD gasoline engines with strong swirl. The experimental investigations in this study focus on the interaction of charge motion and EGR on anti-knock performance and thermal efficiency under different load conditions, and verifies the potential to improve the thermal efficiency of inclined swirl combustion system. The results show that at low-medium load, the tumble-dominated inclined swirl scheme can enhance the effectiveness of EGR in knock suppression, thus reducing the introduction of EGR to avoid its adverse effects on the combustion duration. At medium-high load, although the above benefit wears off, it can enhance the anti-knock performance and thus advance the spark timing by increasing the EGR tolerance. The EGR ratio corresponding to the highest thermal efficiency increases with higher load. The difference in the in-cylinder flow field will affect the combustion rate in a high EGR dilution and high load condition. The scheme adopting the compound intake ports and inverse cuneiform-shaped combustion chamber can improve both EGR tolerance and initial combustion rate under high EGR dilution, with the most significant improvement in thermal efficiency, and the improvement range will increase along with the increase of load.

Predicting Octane Number of Petroleum-Derived Gasoline Fuels from MIR Spectra, GC-MS, and Routine Test Data

Petroleum-derived gasoline is still the most widely used liquid automotive fuel for ground vehicles equipped with spark-ignition engines. One of the most important properties of gasoline fuels is their antiknock performance, which is experimentally evaluated via the octane number (ON). It is widely accepted that the standard methods for ON measuring (RON: research octane number and MON: motor octane number) are very expensive due to the costs of the experimental facilities and are generally not suitable for field monitoring or online analysis. To overcome these intrinsic problems, it is convenient that the ON of gasoline fuels is estimated via faster methods than the experimental tests and allows for acceptable results with acceptable reproducibility. Various ON prediction methods have been proposed in the literature. These methods differ in the type of fuels for which they are developed, the input features, and the analytical method used to underlie the link between input features and ON. The aim of this work is to develop and evaluate three empirical methods for predicting the ON of petroleum-derived gasoline fuels using MIR spectra, GC-MS, and routine test data as input features. In all cases, the chosen analytical method was partial least squares regression (PLSR). The best performance for both MON and RON prediction corresponded with the composition-based model, since it presented lesser evaluation indices (RMSE, MAE, and R2) and more than 80% of residuals were within the established criteria (sum of the reproducibility and the uncertainty of the standard method). Although the routine-test-data-based method performed poorly according to the established criterion, its use could be recommended in cases of scarce data since it showed an acceptable value of R2 and physical consistency. Despite their empirical nature, the proposed prediction models based on MIR (mid-infrared) spectra, GC-MS, and routine test data had the potential to predict the RON and MON of real gasoline fuels commercialized in Colombia.

Tert-Butyl Ethers of Renewable Diols as Oxygenated Additives for Motor Gasoline. Part I: Glycerol and Propylene Glycol Ethers

The study investigates tert-butoxy alkanols (otherwise defined as polyol tert-butyl ethers) that have vicinal tert-butoxy and hydroxy groups in their molecules from the perspective of their usability as oxygenated additives for motor gasoline. A series of propylene glycol mono-tert-butyl ether (PTBE) and glycerol di-tert-butyl ether (di-GTBE) samples were prepared: PTBE by direct acid-catalytic alkylation of diols with tert-butanol, and di-GTBE by alkylation of epichlorohydrin. Adding PTBE and di-GTBE to base motor gasoline was found to improve its antiknock performance: the average blending research octane number to blending motor octane number ratios (bRON/bMON) equaled 120/111 and 124/104 for PTBE and di-GTBE, respectively. Furthermore, the effects of the ether additives on the properties of ethanol-blended base gasoline were characterized. Finally, the study describes the effect of polyol tert-butyl ether additives on the cloud point depression of ethanol-blended gasoline (low-temperature phase stabilization) and demonstrates a positive synergistic effect of adding the ethers mixed with ethanol

Tert-Butyl Ethers of Renewable Diols as Oxygenated Additives for Motor Gasoline. Part I: Glycerol and Propylene Glycol Ethers

The study investigates tert-butoxy alkanols (otherwise defined as polyol tert-butyl ethers) that have vicinal tert-butoxy and hydroxy groups in their molecules from the perspective of their usability as oxygenated additives for motor gasoline. A series of propylene glycol mono-tert-butyl ether (PTBE) and glycerol di-tert-butyl ether (di-GTBE) samples were prepared: PTBE by direct acid-catalytic alkylation of diols with tert-butanol, and di-GTBE by alkylation of epichlorohydrin. Adding PTBE and di-GTBE to base motor gasoline was found to improve its antiknock performance: the average blending research octane number to blending motor octane number ratios (bRON/bMON) equaled 120/111 and 124/104 for PTBE and di-GTBE, respectively. Furthermore, the effects of the ether additives on the properties of ethanol-blended base gasoline were characterized. Finally, the study describes the effect of polyol tert-butyl ether additives on the cloud point depression of ethanol-blended gasoline (low-temperature phase stabilization) and demonstrates a positive synergistic effect of adding the ethers mixed with ethanol.

Potential of high compression ratio combined with knock suppression strategy for improving thermal efficiency of spark ignition stoichiometric natural gas engine

Spark ignition (SI) stoichiometric natural gas (NG) engines could be used to replace diesel engines as power sources in vehicles to meet carbon-emission regulations, which are becoming increasingly stringent. However, the compression ratios (CRs) of SI stoichiometric NG engines are generally lower than those of diesel engines owing to knock limitations. Overcoming the limitations of knocking on CR is significant in improving thermal efficiency and reducing CO2 emissions. In this study, the occurrence and suppression of knock in a high-CR stoichiometric NG engine were studied through numerical simulation. The effects of three knock-suppression strategies, including the Miller cycle with late intake valve closing (IVC), exhaust gas recirculation (EGR), and increasing tumble ratio (TR), on the knock resistance and indicated thermal efficiency (ITE) at a high CR of 15 are discussed. The results show that the knock intensity (KI) increases exponentially to the super-knock level as the spark timing (ST) is advanced. When the CR is increased from 11.5 to 15, the ST needs to be retarded by 25 °CA to suppress the knock, so that the combustion phasing is significantly retarded. At a high CR of 15, by retarding the IVC angle or increasing the EGR rate, the KI is gradually decreased exponentially to below 0.2 MPa and the combustion phasing is retarded less, which allows for better anti-knock performance. An IVC retardation angle of 90 °CA and an EGR rate of 29% achieved maximum ITEs of 46.5% and 47.8%, respectively. At a high CR of 15, with an increase in TR, the KI first increased and then decreased; however, it failed to drop below 0.2 MPa, which delayed the ST, resulting in slight improvement in the ITE. This study provides an effective method to develop stoichiometric NG engines with high efficiencies and low carbon emissions.

Formation of Shaped Charge Projectile in Air and Water.

With the improvement of the antiknock performance of warships, shaped charge warheads have been focused on and widely used to design underwater weapons. In order to cause efficient damage to warships, it is of great significance to study the formation of shaped charge projectiles in air and water. This paper uses Euler governing equations to establish numerical models of shaped charges subjected to air and underwater explosions. The formation and the movement of Explosively Formed Projectiles (EFPs) in different media for three cases: air explosion and underwater explosions with and without air cavities are discussed. First, the velocity distributions of EFPs in the formation process are discussed. Then, the empirical coefficient of the maximum head velocity of EFPs in air is obtained by simulations of air explosions of shaped charges with different types of explosives. The obtained results agree well with the practical solution, which validates the numerical model. Further, this empirical coefficient in water is deduced. After that, the evolutions of the head velocity of EFPs in different media for the above three cases are further compared and analyzed. The fitting formulas of velocity attenuation of EFPs, which form and move in different media, are gained. The obtained results can provide a theoretical basis and numerical support for the design of underwater weapons.

Experimental investigation on the effects of Miller cycle coupled with asynchronous intake valves on the performance of a high compression ratio GDI engine

In this study, a series of comparative experiments were conducted on a gasoline direct ignition (GDI) turbocharged engine to investigate the effects of asynchronous intake valve Miller cycle (AIVMC) on the performance, combustion and emissions characteristics. The results show that using the asynchronous valve closing in the test engine can not only realize the Miller cycle, but also flexibly control the load, effectively reduce pump loss and improve fuel economy compared to the late intake valve closing. The minimum brake specific fuel consumption (BSFC) of the test engine equipped with and without the AIVMC are 235.59 g/kwh and 255.2 g/kwh at the condition of 2600 rpm and brake mean effective pressure (BMEP) 8 bar, which obtains a reduction of 7.7% compared to the baseline engine. In addition, the corresponding brake thermal efficiency (BTE) of test engine used the AIVMC is 35.6%, which is improved 8.2%. Besides, under the same geometric compression ratio, using the AIVMC in the test engine effectively improves the antiknock performance, keeps the 50% combustion location (CA50) closer to top dead center, shortens combustion duration, and expands the load range of low fuel consumption. As for emission performance, compared with baseline engine, though the application of AIVMC has lower mean in-cylinder temperature, the NOx emissions increases at low and medium loads but decreases at high load while HC emissions increases.

Study on Antiknock Performance of Reinforced Concrete Slabs Using Piezoceramic Transducers

Study on Antiknock Performance of Reinforced Concrete Slabs Using Piezoceramic Transducers

Study on the Effects of Ethanol-gasoline Octane Number on Anti-knock Performance in Direct-injection Gasoline Engine

ABSTRACT The high strength technology for gasoline engines improves the thermal efficiency, while at the same time, increasing the knocking tendency. To improve the anti-knock performance of gasoline engines, blending mixture of fuels are needed with higher requirements. In this paper, ethanol/TRF fuel was selected as the gasoline substitute and the effects of fuel octane number and ethanol content on anti-knock performance were simulated in a three-dimensional engine model. The results show that when knock occurs, the knock amplitude is larger at the intake port and the knock onset is earlier at the exhaust port. With the enhancement of anti-knock performance, abnormal combustion such as spontaneous ignition of the end-gas mixture is suppressed, where the turbulent kinetic energy increases in the combustion chamber but decreases at the edge of the cylinder. Also, it is indicated that increasing the RON by 1, mixing 2% volume ethanol, and increasing MON by 1 orderly improve the thermal efficiency. Based on the research and optimization, an evaluation index of anti-knock performance for ethanol-gasoline fuel (EOI*) is proposed, which is suitable for modern engines. From this index, the chemical effect contributes most in the anti-knock performance of ethanol-gasoline mixtures, while the evaporative cooling effect and sensitivity are less and less dominant.

Experimental study on the application of n-butanol and n-butanol/kerosene blends as fuel for spark ignition aviation piston engine

Spark ignition aviation piston engine which mainly equipped in light aircrafts is the important part of aviation power. Due to the particularity of operation conditions, spark ignition aviation piston engine still relies heavily on gasoline. The application of renewable alternative fuel is an effective way to reduce the carbon emissions of air transport industry. Meanwhile, the application of high flash point fuel is expected to improve the safety of aircraft. In this paper, n-butanol was proposed as fuel for spark ignition aviation piston engine to replace gasoline. The engine performance fueled with n-butanol were studied and compared to gasoline. N-butanol had shorter flame development duration and rapid combustion duration than gasoline. The heat release of n-butanol was more concentrated and n-butanol could achieve higher brake thermal efficiency. The CO and NOx emissions of n-butanol had significant advantages over gasoline. However, the application of n-butanol led to an obviously increase in fuel consumption. Then, n-butanol/kerosene mixed fuel with higher energy density were proposed to be the fuel of spark ignition aviation piston engine. Due to the combustion detonation, the knock limited spark timing of n-butanol/kerosene was quite delayed which resulted in the low engine efficiency. Improving the antiknock performance of n-butanol/kerosene based on high octane additives was the key to improve their performance in spark ignition aviation piston engine.

Increasing the Effective AKI of Fuels Using Port Water Injection (Part I)

<div class="section abstract"><div class="htmlview paragraph">Anti-knock index (AKI) is a metric that can be used to quantify the anti-knock performance of a fuel and is the metric used in the United States. AKI is the average of Research Octane Number (RON) and Motor Octane Number (MON), which are calculated for every fuel on a Cooperative Fuel Research (CFR) engine under controlled conditions according to ASTM test procedures. Fuels with higher AKI have better knock mitigating properties and can be run with a combustion phasing closer to MBT in the knock limited operating region of a gasoline engine. However, fuels with higher AKI tend to be costlier and less environmentally friendly to produce. As an alternative, the anti-knock characteristics of lower AKI fuels can be improved with water injection. In this sense, the water injection increases the ‘effective AKI’ of the fuel. The injected water absorbs heat, which lowers the in-cylinder temperatures and mitigates knock, which permits advancing the knock limited CA50 (KLCA50) and reducing fuel consumption for a given speed-load condition. This project focused on quantifying the amount of water required, both as a ratio with fuel, and absolute, to achieve an increase in ‘effective AKI’. This was accomplished by comparing the anti-knock performance of a high AKI reference fuel to lower AKI fuels supplemented with water injection. Tests were conducted at varying speeds and loads to investigate trends in the relationship between effective AKI per unit water injected. The results showed that engine speed does not have a profound effect on the required water-fuel ratio, but as the load is increased, less water is required to increase the effective AKI by a specific amount. The effect of water injection on COV of IMEP was also observed.</div></div>

Performance and Application of Rapid Assembling Anti-blast Wall

With too much emphasis being laid on the antiknock performance of the current anti- blast wall and its mobility thus ignored, in order to strengthen the temporary protective capability of battlefield, a kind of rapid assembling anti-blast wall is proposed, its structural form and assembly method are introduced. The antiknock ability and the durability performance of the anti-blast wall are fully analyzed with the latest application cases, its application in military and civil field are introduced. The application results indicate that the anti-blast wall shows flexible mobility in transportation and assembling, moreover exhibit high adaptive capability, as well as protective capability. So it possesses great value in further research and promotion, and strengthening the combination with other protective technologies is considered to be the future trend.

Numerical investigation on combustion system optimization of stoichiometric operation natural gas engine based on knocking boundary extension

In this work, a computational fluid dynamic model is established based on a natural gas engine and experimental results, and the combustion system of stoichiometric operation natural gas engine (intake manifolds and combustion chambers) is optimized based on knocking boundary extension under high load condition. In addition, the effects of Miller cycle and EGR on the combustion and knocking boundary extension are also explored. Results reveal that the intensity and distribution of in-cylinder turbulent kinetic energy will significantly affect the flame development and combustion characteristics. The combination of spiral intake manifold + K15 chamber shows better performance in antiknock because of the enhanced in-cylinder airflow motion and flame development. In addition, the Miller cycle with the late intake valve close timing of 20 °CA can effectively extend the antiknock performance of the engine under the current operating operation. EGR has limited effect on turbulent kinetic energy, and the primary affective mechanism of EGR on knocking is mainly achieved by changing the in-cylinder temperature during the combustion process. It is found that with tangential and spiral intake manifold + K15 chamber, combined with late intake valve closing (20 °CA) and EGR (30%), the indicated mean effective pressure (IMEP) can be increased by 5.21% within the knocking boundary compared to that of the original combustion system.

A new approach for producing mid-ethanol fuels E30 based on low-octane hydrocarbon surrogate blends

Development of mid-ethanol fuel with an ethyl alcohol content of 20–40% (E30 fuel), which is devoid of phase instability problems and can potentially be applied to automotive technology without modifications, and it is a promising area. One of the promising ways is to develop high-octane Е30 fuel based on cheap low-octane fractions, which will significantly improve the economic parameters of fuel production. This research paper investigates the influence of bioethanol at a concentration of 5–85 wt% on the change in an antiknock performance of low-octane hydrocarbon fractions, involving heavy hydrocracked naphtha and straight run hydrotreated naphtha, as well as low-octane surrogate blends of individual hydrocarbons of various groups, containing n-heptane, isooctane, toluene, p-xylene, cyclohexane, n-pentane, n-hexane, and isooctene. The results indicated that the antiknock performance of bioethanol in low-octane hydrocarbon fractions was increased in the series: olefins <naphthenes <aromatics <paraffins <isoparaffins according to the research method, where it was reached to the maximum in a concentration of 10–30 wt%. What's more, the boundary values of the antiknock performance of bioethanol at a concentration of 20–40 wt% in low-octane hydrocarbon fractions, expressed in octane ethanol blending numbers were investigated as: RONBL = 130–156, MONBL = 108–133.

Mapping K factor variations and its causes in a modern, spark-ignition engine

The Research Octane Number (RON) and the Motor Octane Number (MON) are primary fuel properties that characterize gasoline’s knock resistance in spark ignition engines. The utility of these two metrics, however, has been questioned with advancements in engine technologies that significantly change the thermochemical environment inside the cylinder. The Octane Index, OI = (1-K)·RON + K·MON, has therefore been proposed to characterize the knock resistance in modern engines where K weights the relative contribution of the RON and MON and is primarily determined by engine design and operating conditions. Quantifying the K factor is central to understanding a fuel’s anti-knock performance in a modern spark-ignition (SI) engine.This work therefore determines the map of K over engine operating conditions for a 2-litre, 4-cylinder turbocharged, gasoline direct-injection engine. To achieve this, a novel blending system for primary reference fuels (PRFs) was developed to determine K by matching the knock resistance of a 91.6-RON certification gasoline with a PRF at each operating condition. The K values are determined over the engine map with normal and high intake air and coolant temperatures. At normal operating temperature, K is negative at most knock-limited conditions, consistent with previous findings, whereas at high operating temperatures, K is mostly positive and, indeed, exceeds 1 near 8 bar BMEP and 3000 RPM, demonstrating the relevance of the MON at some conditions of practical significance. Further analysis is conducted via engine simulations to examine the relationship between K and end gas conditions, and a strong correlation is observed between K and the unburned gas temperature at the later stages of combustion. This correlation is argued to have a sound physical basis in the engine’s thermochemistry, supporting the utility of this K factor method.