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Viewing 1 to 30 of 110607
2017-10-08
Technical Paper
2017-01-2392
Matthew Duckhouse, Mark S. Peckham, Harry Bradley
An on-board version of a fast response chemiluminescence analyzer with a 3 millisecond response time enables the recording of high temporal resolution transient NOx emissions during cold start and pull-away, gear changes, speed bumps and other real world transient conditions. Tests were performed on a 1.6 litre turbo GDI vehicle. The data has been correlated with on-board engine data available from the vehicle’s electronic control unit to study the underlying causes of these short-duration events. Exhaust gas was sampled from after the catalyst but before the silencer (muffler) to preserve all high frequency detail and to allow accurate integration of pollutant concentration and measured engine exhaust mass flow. Various aspects of the vehicle’s calibration are seen to contribute to the short-duration bursts of tailpipe emissions which would not be visible with slower response analyzers.
2017-10-08
Technical Paper
2017-01-2184
Vincenzo De Bellis, Fabio Bozza, Daniela Tufano
Nowadays, the development of a new engine is becoming more and more complex due to conflicting factors regarding technical, environmental and economic issues. Hence, the experimental activity has to comply with the above complexities, resulting in increasing cost and duration of engine development. For this reason, the simulation is becoming increasingly important, thanks to its lower financial burden, together with the need of an improved predictive capability. Among the other numerical approaches, the 1D models represent a proper compromise between reliability and computational effort, especially if the engine behavior has to be investigated over a number of operating conditions. The combustion model has a key role in this contest and the research of consistent approaches is still on going. In this paper, two well-assessed combustion models for Spark Ignition (SI) engines are described and compared: the eddy burn-up theory and the fractal approach.
2017-10-08
Technical Paper
2017-01-2182
Xikai Liu, Xingyu Liang, Yonge Wu
According to the study of the soot emission in marine diesel, ,a new reduced mechanism for n-heptane was constructed to describe the combustion process in diesel engine by using sensitivity analysis.Furthermore,verifying the ignition delay time,the laminar flame speed,the flame propagation distance and species profiles in combustion process by using Chemkin Pro in different pressure(13.5atm and 42 atm),initial temperatures and equivalence ratio(0.5 and 1.0).Then,compare the simulated result with the experiment data and the simulated result by using LLNL(lawrence livermore national laboratory)detail mechanism and SKLE(state key laboratory of engine)mechanism.It is demonstrated that the reduced mechanism can not describe the ignition delay time in low temperature.And then,the reduced mechanism was adjusted and optimized to make it more close to the experiment data,and the reduced mechanism were able to predict ignition delay time,laminar flame speed,flame propagation distance and species profiles.The final reduced n-heptane mechanism are more compact compare with the current detailed mechanisms in literature.Thus,this reduced n-heptane mechanism can reduce the pressure of calculation and save the calculation time.
2017-10-08
Technical Paper
2017-01-2209
Christian Ibron
Partially premixed combustion (PPC) can be applied to decrease emissions and increase fuel efficiency in direct injection, compression ignition (DICI) combustion engines. PPC is strongly influenced by how the fuel mixes with oxidizer, which for a given fuel is controlled mainly by (a) the injection, (b) the in-cylinder flow and (c) the geometry and dynamics of the engine. As injection timings can vary over a wide range in PPC combustion deeper knowledge of the in-cylinder flow over the whole compression stroke can improve our understanding of PPC combustion. In computational fluid dynamics (CFD) the in-cylinder flow is sometimes simplified and modeled as a solid body rotation at some time prior to injection in order to produce a realistic flow field at the moment of injection. In real engines the in-cylinder flow motion is governed by the intake manifold, the valve motion and the engine geometry.
2017-10-08
Technical Paper
2017-01-2217
Fushui Liu, Ning Kang, Yikai Li, Pei Wang
The electronic unit pump system, which is widely applied to the heavy-duty diesel engine, belongs to the pulsating high pressure fuel injection system, and the fuel pressure fluctuations have an essential influence on the spray and combustion in the internal combustion engine. Pressure fluctuations are always aroused by the motion of actuators, such as the injector, so it is also an advantage for fault diagnosis and feedback control to ascertain the relationship between the pressure fluctuation and the motion of the actuator. In this study, experiments and 1D simulation were carried on to investigate the fuel pressure fluctuation characteristics and their connection to the transient motion of the needle valve in the injector.
2017-10-08
Technical Paper
2017-01-2246
Ho Teng
Atkinson cycle realized with a late intake valve closing (LIVC) and Miller cycle achieved with an early intake valve closing (EIVC) have been recognized as effective approaches for improving the gasoline engine fuel economy. In both Atkinson and Miller cycles, the engine can be designed with a higher geometric compression ratio for increasing the expansion work and the effective compression ratio is governed by the intake valve close (IVC) timing for the knock control. Duration of the intake event and IVC timing affect not only the pumping loss during the gas exchange, but also have strong influences on the friction torques of the intake cams and the turbulence intensities for the in-cylinder charge motion. The latter governs duration of combustion and EGR tolerance, both of which have impacts on the engine thermal efficiency.
2017-10-08
Technical Paper
2017-01-2242
Boyuan Wang, Changpeng Liu, Zhi Wang, Li Fubai, Yingdi Wang, Yunliang Qi, Xin He, Jian-Xin Wang
A new ignition method is proposed called flame accelerated ignition, which is realized by a flame acceleration tunnel set between the spark plug and the main chamber with annular spoilers inside. The investigation of flame accelerated ignition was experimentally accomplished on both a rapid compression machine with optical accessibility and a single-cylinder heavy duty engine. In rapid compression machine study, synchronous pressure sensing and high-speed photography were used with spark ignition cases tested for comparison. The results show that the combustion process is significantly accelerated by flame acceleration ignition. The combustion duration is shortened by more than 30% under all loads compared with spark ignition. According to the optical results, the axial speed of flame outside the flame acceleration tunnel reaches at least 30 m/s and shows positive correlation with load, which is over 10 times than that of conventional flame propagation caused by spark ignition.
2017-10-08
Technical Paper
2017-01-2277
Xiao Peng, Han Wu, Chia-Fon Lee, Qianbo sun, Fushui Liu
Methanol has been regarded as a potential transportation fuel due to its advanced combustion characteristics and flexible source. However, it is suffering from misfire and high HC emissions problems under cold start and low load conditions either on methanol SI engine or on methanol/diesel dual fuel engine. Hydrogen is a potential addition that can enhance the combustion of methanol due to its high flammability and combustion stability. In the current work, the effect of hydrogen ratio on the laminar flame characteristics of hydrogen-methanol-air mixture under varied equivalence ratios was investigated on a constant volume combustion chamber system coupled with a schlieren setup. A high-speed camera, set at 512X512 pixel and 10000 fps, was used to record the instantaneous images of the flame front during propagating.
2017-10-08
Technical Paper
2017-01-2301
Hongli Gao, Fujun Zhang, Wenwen Zeng, Tianpu Dong, Zhengkai Wang
Abstract:The electronic control of direct injection fuel system,which could improve engine fuel efficiency, dynamics and engine emission performance through good atomization, precise control of fuel injection time and improvement of oil-gas mixture, is the key technology to achieve the stratified combustion and lean combustion. In this paper, a direct injection injector that based on voice coil motor was designed aiming at the technical characteristics of one 800cc two-stroke camless engine. Prior to a one - dimensional simulation model of injector was established by AMEsim and the maximal fuel injection demand was met via the optimization of the main parameters of the injector, the structure of the voice coil motor was optimized by magnetic equivalent circuit method. After that, the maximal flow rate of the injector was verified by the injector bench test while the atomization effect of the injector was verified by using a high-speed camera.
2017-10-08
Technical Paper
2017-01-2324
Nagendra Singh
Biodiesel is an alternate fuel can be use diesel engine with blending in percentage .Bio diesel is created by chemically reacting fatty acids and alcohol by combining vegetable oil with methanol in the presence of a catalyst. Biodiesel is much more suitable for use as an engine fuel having low viscosity however reliability challenges will be there like Low engine power, Low Fuel efficiency, High engine deposits , clogging of fuel and oil filter, High Nox, Fuel property Stability, FIE parts wear , Oil slugging and High maintainability cost etc . There are various experiment, test and validation activity carried out while developments of Bio diesel engine and results were compiled.
2017-10-08
Technical Paper
2017-01-2321
Timothy H. Lee, Gang Li, Han Wu, Tonghun Lee, Alan Hansen
Bio-butanol has been considered as a promising alternative fuel for transportation due to its advantageous physical and chemical properties, but the high recovery and dehydration cost reduced its competitiveness in the fuel market. In order to achieve the bio-fuel advantage, the current work tried to apply and evaluate the upstream products of bio-butanol, Isopropanol-Butanol-Ethanol (IBE). These mixtures are obtained by ABE fermentation and IBE fermentation respectively, as alternative diesel fuel. Isopropanol-Butanol-Ethanol (IBE) is an intermediate product in the IBE fermentation process for producing bio-butanol. The study was carried out in an AVL 5402 single-cylinder diesel engine fueled by IBE-Diesel, ABE-Diesel and neat diesel. During the experiments, the engine speed, engine loads, and injection timings were varied. The results showed that with the addition of IBE in diesel fuel, the engine can still operate smoothly with a set pilot injection.
2017-10-08
Technical Paper
2017-01-2305
Jun Yamauchi, PengBo Dong, Keiya Nishida, Youichi Ogata
With the aim of improving engine performance, recent trend of fuel injection nozzle design followed by engineers and researchers is focusing on more efficient fuel break up, atomization, and fuel evaporation. Therefore, it is crucial to characterize the effect of nozzle geometric design and the injection condition on fuel internal flow dynamics and the consequent fuel-air mixture properties. In this study, the internal flow and spray characteristics generated by the practical multi-hole nozzles with different nozzle hole diameter and injection pressure were investigated in conjunction with a series of computational and experimental methods. Specifically, the CFD commercial code was used to predict the internal flow variation under the different nozzle hole diameter and injection pressure,and the high-speed video observation method was applied to visualize the spray evolution processes under the non-evaporating condition.
2017-10-08
Technical Paper
2017-01-2344
Robert Taylor, Hua Hu, Carl Stow, Robert Mainwaring, Scott Rappaport, Tony Davenport, Sarah Remmert
Future scenarios prepared by Shell anticipate that worldwide energy demand will approximately double by 2050, whilst at the same time, CO2 emissions need to be halved. Therefore, there is great pressure on improving efficiency of all machines, and clearly there is great focus on improving the fuel efficiency of passenger cars. The use of downsized, boosted, gasoline engines, can lead to exceptional fuel economy, and on a well-to-wheels basis, can give similar CO2 emissions to electric vehicles (depending, of course, on how the electricity is generated). A study is reported on a low weight Shell concept car, equipped with a three-cylinder 0.6 litre gasoline engine, which has achieved over 100 miles per imperial gallon, in real world driving conditions.
2017-10-08
Technical Paper
2017-01-2415
Valery Dunaevsky
The film thickness–roughness ratio Λ has been used since the mid-1960s as a criterion for the lubrication conditions in rolling bearings. However, due to an assumed Gaussian distribution of the roughness height amplitudes of the functional surfaces of rolling bearings and other unsubstantiated assumptions concerning the mechanisms of contact interaction, concerns have arisen about the representability of Λ in terms of lubrication. In this study, a more objective Λ-type ratio that does not depend on the law of roughness height distribution and the peculiarities of contact mechanics is introduced and defined as Λz. The relevant range of the new Λ ratio, which identifies a full-film lubrication, is lower than that of its conventional counterpart, and it coincides directionally with contemporary theoretical and experimental results. The study exhibits unique profilometric data of the functional surfaces of the roller bearings, produced by the major bearing manufacturers.
2017-10-08
Technical Paper
2017-01-2416
Anurag Durve
Turbochargers are used throughout the automotive industry to enhance the output of an internal combustion engine without increasing the cylinder capacity. The application of such a mechanical device enables automotive manufacturers to adopt smaller displacement engines, commonly known as engine downsizing. Turbochargers are often used to increase the potential of an already powerful IC engine, similarly 2 stage turbochargers are used to increase potential of already turbocharged IC engine. The emphasis today is to provide a feasible engineering solution to manufacturing economics and “greener” road vehicles. It is because of these reasons that 2 stage turbochargers are now becoming much more popular in automotive industry applications. The aim of this paper is to provide a review on the current techniques used in 2 stage turbocharger matching for already turbocharged diesel engine to enhance its power for all operating zone and also to get better fuel efficiency.
2017-10-08
Technical Paper
2017-01-2409
Erbao Zhang, Yinchun Gong, Jun Deng, Zongjie Hu, Chuanqian Jiang, Zhijun Wu, Liguang Li
Hydrogen fuel will be a potential energy source for internal combustion engines in the future. A promising approach for improving the efficiency and achieving zero-emission is to employ the noble gas argon. The work of this paper aimed at investigating the cyclic variation of argon power cycle engine with fuel of hydrogen. The engine has been modified based on a 0.4 L, one signal cylinder diesel engine into spark ignition engine with a port fuel injection system. The influencing factors on the cyclic variation in the argon power cycle engine with fuel of hydrogen, such as type of working gas, ignition timing, compression ratio (5.6, 6.9, and 7.35), and CO2 fraction in the mixture of argon and oxygen, were test in this study. The results show that compared to air, higher indicated mean effective pressure (IMEP) and better engine operation stability could be achieved under an atmosphere of argon and oxygen.
2017-10-08
Technical Paper
2017-01-2411
Henry Guo
A smart waste-gate (WG) turbocharger controls boost by bypassing turbine flow through the WG port which allows optimizing both low and high speed engine performance. However, the WG port in the turbine housing involves much complex geometry which leads to potential higher thermal stress and plastic strain if design is improper. This paper first presents the common thermal cracking problems at port zone and then shows finite element analysis (FEA) results for one of the design. The predicted location correlates well with the observed failure port location. Then a design study of key parameters for the port is conducted with same boundary conditions. The key parameters include height H, inner diameter D and inner diameter fillet r of the port. Totally 13 designs are studied under package and performance limitation. Accumulated plastic strain from FEA is used to evaluate the effect of design changes.
2017-10-08
Technical Paper
2017-01-2407
Michael Bardon, Greg Pucher, David Gardiner, Javier ariztegui, Roger Cracknell, Heather Hamje, Leonardo Pellegrini, David Rickeard
Low Temperature Combustion using compression ignition may provide high efficiency combined with low emissions of oxides of nitrogen and soot. This process is facilitated by fuels with lower cetane number than standard diesel fuel. Mixtures of gasoline and diesel (“dieseline”) may be one way of achieving this, but a practical concern is the flammability of the headspace vapours in the vehicle fuel tank. A mathematical model is presented that predicts the flammability of the headspace vapours in a tank containing mixtures of gasoline and diesel fuel. Fourteen hydrocarbons and ethanol represent the volatile components. Heavier components are treated as non-volatile diluents in the liquid phase. The non-ideality of the blends of hydrocarbons and ethanol is accounted for using activity coefficients.
2017-10-08
Technical Paper
2017-01-2403
Yanzhao An, R vallinayagam, S vedharaj, Jean-Baptiste MASURIER, Alaaeldin Dawood PhD, Mohammad Izadi Najafabadi, Bart Somers, Bengt Johansson
Low temperature combustion concepts are studied recently to simultaneously reduce NOX and soot emissions. Optical studies are performed to study gasoline PPC in compression ignition (CI) engines to investigate in-cylinder combustion and stratification. It is imperative to perform emission measurements and couple soot and NOX emissions with combustion images. In this research work, we attempt to investigate the soot particulates during the transition from CI to HCCI for gasoline like fuels. The experiments are performed in a single cylinder optical diesel engine that runs at a speed of 1200 rpm. Considering the safety of engine, testing was done at lower IMEP (2 to 3 bar) and combustion is visualized using a high speed camera. From the engine experiments, it is clear that combustion phasing decreases as SOI is swept from late fuel injection timings, before it detaches completely at early injection.
2017-10-08
Technical Paper
2017-01-2406
Wu Yang, Xiuting Yin, Zhang Song ZHAN, Huixian Shen, Huibin Qing, Qingqiang Zeng, Liyun Kang
This work addresses the problem of fatigue strength prediction of crankshaft fillet rolling processes, to reduce friction losses, weights and material costs. It is usually assumed that the effect of fillet rolling process on crankshaft fatigue are conservative and empirically. A predicting method of fatigue strength for ductile cast iron crankshafts is presented, in which the rolling process is considered. The method including two parts: modelling of crankshaft fillet rolling dynamic and predicting fatigue strength of rolling process. The rolling process is solved with an implicit arithmetic and validated by the measurements and tests. Based on the crankshaft dynamic loads calculated by AVL/EXCITE Power Uint, the fatigue effect factors are considered, consisting of compressive residual stresses, work hardening, and reduction of the roughness. The predicting method is applied on a 1.5l I4 gasoline engine.
2017-10-08
Technical Paper
2017-01-2434
Srinivasan Paulraj, Saravanan Muthiah
Traditionally driveline ratios are selected based on trial and error method of proto vehicle testing. This consumes lot of time and increases overall vehicle development effort. Over last few decades, simulation-based design approach has been extensively used to alleviate this problem. This paper describes torque converter and final drive ratio (FDR) selection at concept phase for new Automatic Transmission (AT) vehicle development. Most of the critical data required for simulating vehicle performance and fuel economy (FE) targets were not available (e.g. shift map, clutch slip map, pedal map, dynamic torque, coast down, etc.) at an initial stage of the project. Hence, the risk for assuming right inputs and properly selecting FDR/Torque converter was particularly high. Therefore, a validated AVL Cruise simulation model based on an existing AT vehicle was used as a base for new AT vehicle development to mitigate the risk due to non-availability of inputs.
2017-10-08
Technical Paper
2017-01-2454
Yiqi Jia, Gangfeng Tan, Cenyi Liu, Zehao YANG
In these years, the advantages of using phase change material in the thermal management of electric power battery has been wide spread. Because of the thermal conductivity of most phase change material (eg.wax) is low, many researchers choose to add high conductivity materials(such as black lead). However, the solid-liquid change material has large mass, poor flowability and corrosivity. Therefore, it still stays on experiential stage. In this paper, we use pure water as liquid phase change material (PCM), adopts PCM with an reflux device for thermal management. Meanwhile, utilizing the characteristics of pure water which are economical, easy to prepare, light weight, strong liquidity and hardly corrode the battery to explore the feasibility for water as a PCM for battery thermal management system. We use CATIA to build battery model and FloEFD to simulate temperature distribution of battery during its working stage.
2017-10-08
Technical Paper
2017-01-2289
Chunze Cen, Han Wu, Chia-Fon Lee, Shuxin Hao, Fushui Liu, Yikai Li
Droplets impacting onto the heated surface is a typical phenomenon either in CI engines or in GDI SI engines, which is regarded significant for their air-fuel mixing. Meanwhile, alcohols including ethanol and butanol, has been widely studied as internal combustion engine alternative fuels due to their excellent properties. In this paper, under different component ratio conditions, the ethanol-butanol droplet impacting onto the heated aluminum surface has been studied experimentally. The falling height of the droplets were set at 5cm. A high-speed camera, set at 512×512pixels, 5000 fps and 20 μs of exposure time,was used to visualize the droplet behavior impinging onto the hot aluminum surface. The impact regimes of the binary droplet were identified. The result showed that the Leidenfrost temperature of droplets was affected by the ratio of ethanol to butanol. The higher the content of butanol in the droplet, the higher the Leidenfrost temperature.
2017-10-08
Technical Paper
2017-01-2395
Arjun Prakash, Allen Aradi, William Imoehl, Phil Armitage
The impact of fuel composition (ethanol and aromatic content) and injector design on particulate number generation was studied in a 1.0L displacement direct injection spark ignition engine. Two types of engine tests that mimic real-life vehicle operation were carried out using a matrix of eight fuels and two injectors. It was found that the DISI injector design had the biggest impact on the extent of particulate number generation. An injector prototype designed to meet Euro 6c specifications for PN (6*10^11 particles/km) resulted in much lower PN values compared to those obtained using a production injector currently available in the market. The impact of fuel composition on PN was apparent only during engine operation with the production injector wherein, ethanol (E10) containing fuels (match-blended for aromatics and octane quality) qualitatively resulted in higher PN values compared to non-ethanol containing fuels.
2017-10-08
Technical Paper
2017-01-2400
Hu Li, Yanlong Wu, Jason Ferns, Gordon Andrews
Hydrogenated vegetable oil (HVO) diesel fuels have potential to provide reduced carbon footprint in diesel engines and reduce exhaust emissions. Therefore it is a strong candidate for transport and diesel powered machines including electricity generators and other off-road machines. In this research, a waste cooking oil derived HVO diesel was investigated for its combustion performance including ignition delay and heat release, and particulate number emissions including size segregated values. The results were compared to the standard petroleum diesel. A 3 litre direct injection intercooled IVECO diesel engine equipped with EGR was used which has a maximum power output of 96kW and is EURO5 emission compliant. The engine was equipped with an integrated DOC and DPF aftertreatment system. Both the upstream and downstream of the aftertreatment emissions were measured. The tests were conducted at different RPM and loads at steady state conditions.
2017-10-08
Technical Paper
2017-01-2213
Satoshi Hokimoto, Tatsuya Kuboyama, Yasuo Moriyoshi, Minoru Iida, Takahiro Watanabe
Reduction in the cycle-to-cycle variation (CCV) of combustion in internal combustion engines has been required because CCV affects fuel consumption, emissions and drivability. CCV becomes stronger at low load or lean / diluted burn conditions. Specifically, the factors that cause CCV of combustion are supposed to variations of in-cylinder flow, fuel distribution, temperature distribution, residual gas distribution and ignition energy in each cycle. However, it is impossible to measure and analyze minutely these factors in a production engine. In this study, CCV of the combustion and in-cylinder phenomena in the same cycle of PFI gasoline engine were investigated by using an optical single-cylinder engine. This optical engine can observe the whole combustion chamber by the quartz glass cylinder and pent-roof window. CCV of flow in the cylinder during continuous 45 firing cycles was measured by Time Resolved Particle Image Velocimetry (TR-PIV) technique.
2017-10-08
Technical Paper
2017-01-2210
Masayoshi Matsuda, Takeshi Yokomori, Norimasa Iida
The thermal efficiency of a spark­ignition (SI) engine must be improved to reduce both environmental load and fuel consumption. Although lean SI engine operation can strongly improve thermal efficiency relative to that of stoichiometric SI operation, the cycle-to-cycle variation (CCV) of combustion increases with the air dilution level. Combustion CCV is caused by CCVs of many factors, such as EGR, spark energy, air-fuel ratio, and in-cylinder flow structure related to engine speed. This study focuses on flow structures, especially the influence of a tumble structure on flow fluctuation intensity near ignition timing. We measured the flow field at the vertical center cross section of an optically accessible high-tumble flow engine using time-resolved particle image velocimetry. There are many factors considered to be sources of CCV, we analyzed three factors: the intake jet distribution, distribution of vortex core position and trajectory of the fluid particle near the spark plug.
2017-10-08
Technical Paper
2017-01-2219
Xihui Wang
Conventional heat transfer fluids used for cooling fluids in vehicle cooling water jacket have relatively poor heat transfer performance.One method for enhance heat transfer in cooling-jacket uses nanofluids. Nanofluids have heat transfer enhancement merits .In the present study, the numerical simulation on Fe3O4 nanofluid flow in cooling water jacket of Gasline direct injection engine wax performed using computational fluid dynamics ( CFD) software FLUENT. The heat transfer coefficient of nanofluids was calculated and verified by experiment. Fe3O4 nano-particles were used in mixture of water/ethylene glycol as a base fluid. The thermal performance of the nanofluid was studied, also the thermal performance of a cooling-jacket was studied with CFD software. The simulation was performed for different volumetric concentrations of(1%,2%,5%) nanofluids of different engine speeds.
2017-10-08
Technical Paper
2017-01-2232
Ho Teng
Atkinson cycle realized with a late intake valve closing (LIVC) and Miller cycle achieved with an early intake valve closing (EIVC) have been recognized as effective approaches for improving the gasoline engine fuel economy. In both Atkinson and Miller cycles, the engine can be designed with a higher geometric compression ratio for increasing the expansion work and the effective compression ratio is governed by the intake valve close (IVC) timing for the knock control. Duration of the intake event and IVC timing affect not only the pumping loss during the gas exchange, but also have strong influences on the friction torques of the intake cams and the turbulence intensities for the in-cylinder charge motion. The latter governs duration of combustion and EGR tolerance, both of which have impacts on the engine thermal efficiency.
2017-10-08
Technical Paper
2017-01-2237
K. Gopal Duleep
The overall objectives of this study are to establish the relationship between a spark ignition, or Otto cycle, engine energy efficiency and the octane number of the fuel through a comprehensive review of recently published literature. The efficiency of the ideal Otto cycle is a function of the compression ratio, but increasing compression ratio is limited by the onset of knock, which can be prevented by increasing fuel octane number. Hence, in an ideal case, there is a direct connection between engine efficiency and fuel octane number. In the real world, other factors also contribute to the relationship and spark timing is the primary control variable that affects both knock and efficiency. This analysis explores the relationship between efficiency and octane number.
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