High Octane Number Fuels Research Articles

Low Temperature Heat Release and ϕ-Sensitivity Characteristics of Iso-Octane/Air Mixtures

ABSTRACT Chemical energy release from high octane number fuels via low temperature heat release (LTHR) can help develop high-efficiency gasoline engines by promoting ultra-lean combustion in spark ignition engines and improving combustion control in gasoline compression ignition engines. A recently developed experimental technique that permits isolated LTHR investigations in motored engines was used to characterize the LTHR behavior of iso-octane/air mixtures ranging in strength from to at multiple inlet temperature conditions ( to °C). LTHR changes were studied by observing variations in exhaust CO emissions and exhaust temperature increase. Observed heat release results were explained using cylinder mixture pressure-temperature histories alongside supporting chemical kinetics modeling estimates of mixture reactivity in the form of chemical ignition delay (ID) time. The effects of fuel enrichment on iso-octane/air mixture reactivity were found to be non-uniform and dependent on mixtures’ thermal state trajectories in the LTHR ID peninsula. LTHR intensity measurements were used to discuss changes in mixture sensitivity at different engine inlet conditions. It was shown that by appropriately adjusting mixture thermal conditions via charge cooling from direct fuel injection and intake air heating, reactivity enhancements could be exploited maximally; and strong, positive, linear sensitivity of around 10 J per 0.1 increase in could be realized across a wide range of equivalence ratios from 0.05–1.2. It was also found that dominance of charge cooling effects at rich conditions resulted in negative and zero sensitivity regions.

Study of the Effect of Research Octane Number on the Auto-Ignition of Lubricant Oil Surrogates (n-Hexadecane).

Engine oil is considered one of the sources for pre-ignition in downsized boosted direct injection spark-ignited engines. When interacting with fuel sprayed in the combustion chamber, engine oil forms an ignitable mixture and can cause an ignition event before firing the spark plug. Because high research octane number (RON) fuels are difficult to auto-ignite and tend to suppress the knock in an internal combustion engine, studying their interaction with engine oil is essential. Hence, in the current study, a suitable lubricant oil surrogate, namely, n-hexadecane, is mixed with iso-octane and n-heptane at different concentrations to investigate the auto-ignition behavior at elevated pressures. Five sets of fuels (PRF0, PRF20, PRF50, PRF80, and PRF100) were prepared to get a wide range of RONs and blended with n-hexadecane at 15, 25, 35, and 45% mixture concentrations (vol %). These experiments were conducted in a constant volume combustion chamber, keeping the initial temperature constant at 300 °C. A single droplet of the mixture was suspended on a thermocouple bead to record the droplet’s lifetime temperature. It was observed that hexadecane mixed with PRF0, PRF20, PRF50, and PRF80 showed similar auto-ignition behaviors. The time of ignition (TI) for these mixtures initially increased until 25% concentration of the fuel in n-hexadecane, and further addition of fuels to 35% and higher concentrations showed a gradual decrease in TI. Ignition of mixtures with 35% and 45% fuel concentrations is attributed to n-heptane, as its low temperature chemistry is the dominant factor in its high reactivity compared to iso-octane. TI increased with the increasing concentration of PRF100 mixtures in hexadecane, unlike other PRF fuels tested in this study. This is because iso-octane is a high RON fuel with a higher auto-ignition temperature, making it challenging to auto-ignite.

Impact analysis of partially premixed combustion strategy on the emissions of a compression ignition engine fueled with higher octane number fuels: A review

This paper reviews the effect of a partially premixed combustion strategy on the exhaust emission of a diesel engine fuelled with high research octane number fuels. For the past few years, researchers have been aiming to decrease the soot and NOx emission simultaneously and maintain high engine efficiency in diesel engines by improving the combustion which is achieved by optimizing the fuel injection tactics. Single fuel and split fuel (pilot/main) injection tactics are used in the partially premixed combustion (PPC) strategy of the diesel engine to achieve stable combustion and less soot and NOx emission. The PPC strategy in diesel engine can be easily achieved with high octane number fuel resulting in prolonged ignition delay. The air/fuel mixing would be improved by virtue of longer ignition delay (ID) and as a result, soot emission decreases in the partially premixed compression ignition (PPCI) engine. Additionally, higher octane number fuels (i.e., Ethanol, Methanol and Butanol) improve the charge cooling effect, resulting in reduced NOX emissions. Thus, the combined use of PPC mode diesel engine along with high octane number fuels in modern CI engine could be a favourable upcoming solution to meet the strict exhaust emission legislation and reduce the dependence on fossil fuels.

Effect of piston bowl geometry and compression ratio on in-cylinder combustion and engine performance in a gasoline direct-injection compression ignition engine under different injection conditions

Low temperature combustion (LTC) of high-octane number fuels in compression ignition engines offers an opportunity to simultaneously achieve high engine thermal efficiency and low emissions of NOx and particulate matter without using expensive after-treatment technologies. LTC engines are known to be sensitive to the operation conditions and combustor geometry. It is important to understand the fundamental flow and combustion physics in order to develop the technology further for commercial application. A joint numerical and experimental investigation was conducted in a heavy-duty compression ignition engine using a primary reference fuel with an octane number of 81 to investigate the effects of injection timing, piston geometry, and compression ratio (CR) on the fuel/air mixing and combustion covering different regimes of LTC engines, homogeneous charge compression ignition (HCCI), partially premixed combustion (PPC), and the transition regime from HCCI to PPC. The results show that with the same combustion timing, a higher CR leads to a lower NOx, but a higher emission of UHC and CO. The piston geometry shows a significant impact on the combustion and emission process in the transition regime while it has minor influence in the HCCI and PPC regimes. It is found that high engine efficiency and low emissions of NOx, CO and UHC can be achieved in the earlier PPC regime and later transition regime. The fundamental reason behind this is the stratification of the mixture in composition, temperature and reactivity, which is dictated by the interaction between the spray and the cylinder/piston walls.

Analysis of the Water Addition Efficiency on Knock Suppression for Different Octane Ratings

<div class="section abstract"><div class="htmlview paragraph">Water injection can be applied to spark ignited gasoline engines to increase the Knock Limit Spark Advance and improve the thermal efficiency. The Knock Limit Spark Advance potential of 6 <i>°CA</i> to 11 <i>°CA</i> is shown by many research groups for EN228 gasoline fuel using experimental and simulation methods. The influence of water is multi-layered since it reduces the in-cylinder temperature by vaporization and higher heat capacity of the fresh gas, it changes the chemical equilibrium in the end gas and increases the ignition delay and decreases the laminar flame speed. The aim of this work is to extend the analysis of water addition to different octane ratings. The simulation method used for the analysis consists of a detailed reaction scheme for gasoline fuels, the Quasi-Dimensional Stochastic Reactor Model and the Detonation Diagram. The detailed reaction scheme is used to create the dual fuel laminar flame speed and combustion chemistry look-up tables. The Detonation Diagram is used as a novel approach in the Quasi-Dimensional Stochastic Reactor Model to evaluate the auto-ignition characteristic in the end gas and determine if it is a harmless deflagration or developing detonation. First, the Quasi-Dimensional Stochastic Reactor Model is trained for three engine operating points and a RON95 E10 fuel. Its performance is evaluated based on experimental results of a single cylinder research engine. Subsequently, different spark timings and water-fuel ratios are investigated for different Primary Reference Fuels. The results outline that water addition can effectively reduce the strength of auto-ignition in the end gas for different Primary Reference Fuels. Thereby, it can be stated that the reduction of the auto-ignition strength through water addition by 50 - 80 <i>%</i> water-fuel ratio for high octane number fuels corresponds to the spark timing delay of 6 <i>°CA</i> or an increase of research octane number by 10 points.</div></div>

Rational design of syngas to isoparaffins reaction route over additive dehydrogenation catalyst in a triple-bed system

The product of an ideal Fischer-Tropsch synthesis (FTS) reaction contains mainly linear hydrocarbons (paraffins and olefins) with limited selectivity for isoparaffins. In this work, a triple-bed with Co-SiO2 followed by ZnO-SiO2 and ZSM-5 catalysts is employed to demonstrate a promising route to enhance isoparaffins in the FTS reaction. The rationale of this route involves induction of olefins into the hydrocarbon stream prior to isomerization. Optimum olefin induction was achieved with 2%ZnO-SiO2 catalyst. The FTS reaction results showed remarkably high selectivity, ca. ~40% for isoparaffins, thus giving high prospects as a new route to synthesize high octane number fuels from syngas.

Experimental study of the combustion and emission characteristics of ethanol, diesel-gasoline, n-heptane-iso-octane, n-heptane-ethanol and decane-ethanol in a constant volume vessel

This work investigates the effect of fuel reactivity, mixture preparation (premixed or diffusive) and equivalence ratio (φ = 0.6, 1.0) on the combustion and emission characteristics of ethanol, diesel-gasoline, n-heptane-iso-octane, n-heptane-ethanol and decane-ethanol in a constant volume bomb. It provides the direction to improve the combustion efficiency and reduce the pollutant emissions for the internal combustion engines. The fuel selection criterion is to establish the fuel reactivity gradient by blending the high and low octane number fuels. The main conclusions are summarized below: First, the premixed fuel-lean combustion, also known as homogeneous charge autoignition (HCAI), can improve the combustion efficiency by elevating the peak pressure and reducing the combustion duration. The ethanol combustion efficiency increases from 41.0% at 1.0-D condition to 68.7% at 1.0-P condition by breaking the limit of the fuel-air mixing rate, and finally reaches 72.8% at 0.6-P condition through increasing the oxygen concentration and facilitating the hydrocarbon oxidation. Second, the combination of the high reactivity (low RON) and high volatility fuels can further improve the combustion efficiency that the former acts as the distributed ignition source and the latter forms the homogeneous charge. The combustion efficiency of n-heptane-ethanol at 0.6-P condition reaches 97.2%. Third, the HCAI can reduce the NOx emission by enhancing the mixture uniformity, constructing high dilution to lower the peak combustion temperature. Fourth, the premixed fuel-lean combustion produces higher CO and HC emission compared to diffusive combustion due to the relatively low reaction temperature. Fifth, the premixed fuel-lean combustion can significantly reduce the particle mass and number concentration by decreasing the production of the accumulation mode particles. Sixth, the high volatility/RON fuel (such as ethanol) alone is not the best candidate for HCAI combustion because their high autoignition resistance makes it difficult to ignite spontaneously and produce a large number of unburned hydrocarbons. Then they nucleate to form new particles or condense on solid particles.

The effect of ethanol direct injection on knock mitigation in a gasoline port injection engine

In the development of downsizing and high efficiency spark ignition (SI) engine, overcoming the knock is crucial. One method to suppress knock is to use with high octane number fuels as additives. However, in the current pre-blended fuel such as E10, the blending ratio cannot be varied with the engine operation conditions. The novel ethanol direct injection plus gasoline port injection (EDI+GPI) provides the opportunity to solve the fuel blending problem. Most importantly, EDI+GPI has great potential in anti-knocking. By directly injecting ethanol into the combustion chamber, blending ratio can be adjusted according to the engine conditions and the engine’s anti-knocking ability will be strengthened by not only the ethanol’s high octane rating but also its great latent heat. In the work, the effect of EDI on suppressing the knock caused by advancing spark timing and increasing inlet air pressure were experimentally investigated on a 250cc single cylinder motorcycle engine equipped with an EDI+GPI system. Experimental results showed that compared with GPI and gasoline direct injection (GDI), EDI+GPI effectively mitigated engine knock and permitted more advanced spark timing. In the ethanol energy ratio (EER) range from 15% to 35%, every 2% or 3% increment of EER permitted about 2 CAD advance of knock limited spark advance (KLSA). EDI+GPI also showed benefits to combustion, indicated thermal efficiency and emissions (HC and CO) due to the advanced spark timing and ethanol’s oxygen content and fast laminar flame speed. In conditions simulating turbocharging, compressed air was used to increase the inlet air pressure from 1.0 to 1.4 atmospheric pressure with the EER increased to handle the raised knock tendency. Indicated thermal efficiency was increased with the increase of inlet air pressure. Exhaust gas emissions in terms of ISCO, ISNO and ISHC increased with the increased inlet pressure and major combustion duration decreased with the increase of inlet pressure. Overall, the results demonstrated the potential of EDI+GPI in anti-knocking and consequently increasing the thermal efficiency in small engines.

高オクタン価燃料自着火時の低温度酸化反応の挙動

高オクタン価燃料自着火時の低温度酸化反応の挙動

Control of the low-load region in partially premixed combustion

Partially premixed combustion (PPC) is a low temperature, direct-injection combustion concept that has shown to give promising emission levels and efficiencies over a wide operating range. In this concept, high EGR ratios, high octane-number fuels and early injection timings are used to slow down the auto-ignition reactions and to enhance the fuel and are mixing before the start of combustion. A drawback with this concept is the combustion stability in the low-load region where a high octane-number fuel might cause misfire and low combustion efficiency. This paper investigates the problem of low-load PPC controller design for increased engine efficiency. First, low-load PPC data, obtained from a multi-cylinder heavy- duty engine is presented. The data shows that combustion efficiency could be increased by using a pilot injection and that there is a non-linearity in the relation between injection and combustion timing. Furthermore, intake conditions should be set in order to avoid operating points with unfavourable global equivalence ratio and in-cylinder temperature combinations. Model predictive control simulations were used together with a calibrated engine model to find a gas-system controller that fulfilled this task. The findings are then summarized in a suggested engine controller design. Finally, an experimental performance evaluation of the suggested controller is presented.

Octane rating effects of direct injection fuels on dual fuel HCCI-DI stratified combustion mode with port injection of n-heptane

Experimental study on dual fuel HCCI-DI stratified combustion mode is investigated with port injection of n-heptane and direct injection of primary reference fuels (PRFs) with different octane numbers from 0 to 100. Firstly, in-cylinder stratifications of mixture concentration, composition, and temperature for this HCCI-DI combustion mode were numerically simulated. The effects of the octane number of the DI fuel, the overall equivalence ratio and the premixed fuel fraction by port injection on the combustion, emissions and performance characteristics are studied. Further, the premixed fuel fraction in this dual fuel HCCI-DI stratified combustion mode is optimized based on the octane rating of the DI fuels. It was found that at lower premixed ratio of HCCI-DI combustion, dual-fuel sequential combustion was observed when high octane number fuels were used as directly injected fuel. And the ignition of the direct injected fuels was mainly determined by the active radicals or thermal energy-active radical. At large premixed ratio, the ignition of direct injected fuels was determined by the thermal-atmosphere but almost not influenced by partial equivalence ratio of DI fuels and their octane number.

Combustion Mode Design with High Efficiency and Low Emissions Controlled by Mixtures Stratification and Fuel Reactivity

This paper presents a review on the combustion mode design with high efficiency and low emissions controlled by fuel reactivity and mixture stratification that have been conducted in the authors’ group, including the charge reactivity controlled homogeneous charge compression ignition (HCCI) combustion, stratification controlled premixed charge compression ignition (PCCI) combustion, and dual-fuel combustion concepts controlled by both fuel reactivity and mixture stratification. The review starts with the charge reactivity controlled HCCI combustion, and the works on HCCI fuelled with both high cetane number fuels, such as DME and n-heptane, and high octane number fuels, such as methanol, natural gas, gasoline and mixtures of gasoline/alcohols, are reviewed and discussed. Since single fuel cannot meet the reactivity requirements under different loads to control the combustion process, the studies related to concentration stratification and dual-fuel charge reactivity controlled HCCI combustion are then presented, which have been shown to have the potential to achieve effective combustion control. The efforts of using both mixture and thermal stratifications to achieve the auto-ignition and combustion control are also discussed. Thereafter, both charge reactivity and mixture stratification are then applied to control the combustion process. The potential and capability of thermal-atmosphere controlled compound combustion mode and dual-fuel reactivity controlled compression ignition (RCCI)/highly premixed charge combustion (HPCC) mode to achieve clean and high efficiency combustion are then presented and discussed. Based on these results and discussions, combustion mode design with high efficiency and low emissions controlled by fuel reactivity and mixtures stratification in the whole operating range is proposed.

The Low Load Limit of Gasoline Partially Premixed Combustion Using Negative Valve Overlap

Partially premixed combustion has the potential of high efficiency and simultaneous low soot and NOx emissions. Running the engine in partially premixed combustion mode with high octane number fuels has the advantage of a longer premix period of fuel and air which reduces soot emissions, even at higher loads. The problem is the ignitability at low load and idle operating conditions. The objective is to investigate different multiple-injection strategies in order to further expand the low load limit and reduce the dependency on negative valve overlap in order to increase efficiency. The question is, what is the minimum attainable load for a given setting of negative valve overlap and fuel injection strategy. The experimental engine is a light duty diesel engine equipped with a fully flexible valve train system. The engine is run without boost at engine speed 800 rpm. The fuel is 87 RON gasoline. A turbocharger is typically used to increase the boost pressure, but at low engine speed and load the available boost is expected to be limited. The in-cylinder pressure and temperature around top-dead-center will then be too low to ignite high octane number fuels. A negative valve overlap can be used to extend the low engine speed and load operating region. But one of the problems with negative valve overlap is the decrease in gas-exchange efficiency due to heat-losses from recompression of the residual gases. Also, the potential temperature increase from the trapped hot residual gases is limited at low load due to the low exhaust gas temperature. In order to expand the low load operating region further, more advanced injection strategies are investigated.

Comparison of Negative Valve Overlap (NVO) and Rebreathing Valve Strategies on a Gasoline PPC Engine at Low Load and Idle Operating Conditions

Gasoline partially premixed combustion (PPC) has the potential of high efficiency and simultaneous low soot and NOx emissions. Running the engine in PPC mode with high octane number fuels has the advantage of a longer premix period of fuel and air which reduces soot emissions. The problem is the ignitability at low load and idle operating conditions. In a previous study it was shown that it is possible to use NVO to improve combustion stability and combustion efficiency at operating conditions where available boosted air is assumed to be limited. NVO has the disadvantage of low net indicated efficiency due to heat losses from recompressions of the hot residual gases. An alternative to NVO is the rebreathing valve strategy where the exhaust valves are reopened during the intake stroke. The net indicated efficiency is expected to be higher with the rebreathing strategy but the question is if similar improvements in combustion stability can be achieved with rebreathing as with NVO. The results show that the rebreathing valve strategy has similar improvements on combustion stability as NVO when the same fuel injection strategy is used. This work also includes results with the NVO valve strategy where a fuel injection is added during the NVO. When a fuel injection is added during the NVO, an additional improvement on combustion stability can be seen which is unmatched by the rebreathing valve strategy. (Less)

An investigation of partially premixed compression ignition combustion using gasoline and spark assistance

Nowadays the automotive scientific community and companies are focusing part of their efforts on the investigation of new combustion modes in Compression Ignition (CI) engines, mainly based on the use of locally lean air–fuel mixtures. This characteristic, combined with exhaust gas recirculation, provides low combustion temperatures that reduce pollutant formation. However these combustion concepts have some shortcomings, related to combustion phasing control and combustion stability under the light load engine operating range which must be overcome. The aim of this work is focused on the study of the integration of phasing and cycle-to-cycle repeatability control by means of an ignition spark plug system in a CI engine working under partially premixed charge (PPC) in order to overcome the lack of combustion stability in light load conditions when very low fuel reactivity is used. To achieve this objective, experimental tests have been carried out in a single cylinder optical engine combining broadband luminosity images with cylinder pressure derived heat release rate analysis. Research results reveals the spark assistance as a proper methodology to provide temporal and spatial control over the combustion process solving the lack of cycle to cycle control on the highly premixed compression ignition modes overall in light loads with high octane number (ON) fuels. Additionally, different stages have been identified in the combustion mode. The process starts with the spark discharge, which produces a flame kernel around the spark plug that later evolves to a premixed flame front. This premixed flame front heats unburned mixture and progresses into an auto-ignition combustion that burns out the rest of the charge with higher light intensity and finally an extinction of combustion process. Finally, the effect of injected fuel mass on the combustion mode has been also tested. An increase in the injected fuel mass has a positive effect on the assistance of the spark in the combustion process for both, combustion stability and cycle to cycle control.

HC2-2 Study on Auto-ignition Characteristics of Ethanol and ETBE Blended Fuels in a Gasoline HCCI Engine(HC: HCCI Combustion,General Session Papers)

Bio-fuels such as ethanol (EtOH) and ethyl tert-butyl ether (ETBE) are used as blending components in gasoline for carbon neutralization. These oxygenates are also recognized as high octane number fuels, which are acceptable for spark ignition (SI) combustion, as they inhibit end-gas auto-ignition (partly leading to knocking). However, for homogeneous charge compression ignition (HCCI) combustion, excess delay in ignition timing may occur as an undesirable effect, leading to misfiring or incomplete combustion. In this work, knocking phenomenon and HCCI combustion characteristics of ethanol and ETBE blended gasoline fuels with same octane numbers have been experimentally studied. Chemical reaction simulations were also conducted for further understanding. Experimental work was performed in a single cylinder gasoline engine with compression ratio set to 14.0. Intake air was heated at HCCI combustion operation. SI combustion test results show that when the same octane number fuels are used, ethanol and ETBE have no effect on knocking limit. On the other hand, HCCI combustion results indicate that ethanol retards ignition timing at low intake temperature condition, whereas ignition advancement is observed at high intake temperature condition. ETBE acted as an ignition accelerator for all intake temperatures. Based on these results, an empirical equation is proposed for HCCI timing prediction of the tested blended fuels.

Gasoline partially premixed combustion: high efficiency, low NOx and low soot by using an advanced combustion strategy and a compression ignition engine

A light-duty engine Volvo D5 was run with gasoline to demonstrate that high-octane number fuels, in compression ignition engines, are able to achieve high effi ciency, low NOx and soot simultaneously. An advanced three stage injection strategy was developed. A load sweep was performed between 6 and 17 bar IMEP and 2000 rpm. Gross indicated effi ciency stays fairly constant at 47% with very low NOx and soot. In the second section of the paper, diesel was compared with gasoline, while in the fi nal part the commercial 140°UA nozzle was compared with the narrower one, 120°, used in the above-mentioned experiments.

Computational Fluid Dynamic Modelling a Heavy-Duty Compression-Ignition Engine Fuelled with Diesel and Gasoline-Like Fuels

This paper presents a comprehensive investigation of a compression—ignition (CI) heavy-duty engine fuelled with diesel and gasoline-like fuels. A state-of-the-art engine computational fluid dynamics (CFD) tool was used to explore the influences of the physical and chemical properties of diesel and gasoline-like fuels (no. 91 gasoline and E10) on spray development, auto-ignition and combustion processes, and pollutant formation. The CFD simulation results were found to be consistent with available experimental measurements, both qualitatively and quantitatively. The results indicate that gasoline-like fuels are able to achieve better premixed charge in CI engines owing to their higher volatility and lower ignitability compared to diesel fuel, which promotes efficient, clean, and low temperature combustion. However, the high combustion pressure rise rate becomes problematic under some circumstances, especially for high octane number fuels, such as E10. Both previous experimental measurements and the present numerical results show that gasoline-like fuels have great potential to be used in future CI engines, but the injection strategies and injection system have to be optimized based on the fuel properties.

CT1-3: Difference of Reaction Schemes on Low Initial Temperature Conditions with LTO Reactions and High Initial Temperature Conditions Skipping Them(CT: Combustion, Thermal and Fluid Science,General Session Papers)

By using "Contribution Matrices", the authors had clarified that a major reaction path during thermal ignition preparation phases of DME and n-heptane was a set of reactions named "H_2O_2 reaction loop", and suggested that it may be a universal rule that the heat accumulated by this loop plays a dominant role in preparing the thermal ignition. In the present study, this suggestion was confirmed by using a higher octane number fuel, iso-octane, and by changing the initial temperature. It was confirmed that in all cases, an ignition delay, a period of the thermal ignition preparation phase, depends on the H_2O_2 concentration at the beginning of this phase. Reaction path analyses on higher initial temperature conditions skipping reactions in LTO (cool flame) and NTC ranges result in lower H_2O_2 concentrations and lower heat release during thermal ignition preparation phases. Low and high octane number fuels show similar ignition characteristics when the initial temperature is higher than NTC range temperatures. When a low octane number fuel reacts at a lower initial temperature than NTC range temperatures, the fuel is given an "H_2O_2 bonus by LTO".

Alaska North Slope crude oil price and the behavior of diesel prices in California

This paper first of all summarized the auto-ignition mechanism of high cetane and high octane number fuels from the aspect of chemical reaction kinetics with the main purpose of explaining different auto-ignition characteristics of the two kinds of fuel and providing a classification of fuels with the same ignition principles. High cetane number fuels cover major real compression-ignition internal combustion engine fuels and references fuels in use, including straight-chain alkanes, straight-chain ethers, straight-chain esters and cetane number improvers while high octane number fuels cover major real spark-ignition internal combustion engine fuels and references fuels in use, including hydrogen, carbon monoxide, small molecular alkanes, small molecular ethanol, branched alkanes, cycloalkanes, light olefins, simple aromatic hydrocarbons and gasoline antiknock branched ethers. On this basis, 8 representative high octane number fuels were selected for mixing with the high cetane number fuel n-heptane to study the ignition characteristics of mixed fuels in order to find mechanism and corresponding rules.