Future Engine Designs Research Articles

Simulation of Dual Combustion Cycle in Internal Combustion Engines using MATLAB

The aim of this study is to develop a comprehensive mathematical model to accurately represent the dual combustion cycle in internal combustion engines, with a focus on improving combustion efficiency and reducing emissions. The novelty of this research lies in the integration of advanced combustion models within the mathematical framework to capture the unique characteristics of dual combustion cycles. The model will consider factors such as combustion characteristics, fuel-air mixing, heat transfer, and emissions. By accurately simulating the dual combustion cycle, valuable insights can be gained into the complex interactions occurring within the engine, leading to the development of optimized engine design and control strategies. The proposed model will be implemented using MATLAB, which offers flexibility and computational efficiency. The results obtained from the simulation can be validated against experimental data to ensure the accuracy and reliability of the model. This study is expected to contribute to the advancement of dual combustion cycle technology and provide valuable guidance for the design and optimization of future internal combustion engines.

Hybrid SWOC-AHP Analysis of Two-Stroke Twin Spark Engine

A two-stroke engine is a promising device that provides a high power-to-weight ratio in automobiles. In recent times, the twin-spark configuration has shown advantages over the single-spark configuration. However, the rapid combustion associated with the twin-spark configuration leads to a higher NO x emission. Therefore, it is important to determine its strength-weakness-opportunity-challenges (SWOC). It is also important to prioritize the SWOC factors and sub-factors connected with the twin spark two-stroke engine. Thus, the primary aim of the current investigation is to perform the hybrid SWOC-analytical hierarchy process (AHP) analysis for producing the quantifiable priorities for the factors of the two-stroke twin spark configuration. Additionally, the rank-stability of SWOC factors is investigated using sensitivity analysis. From the results, challenge factors emerged to be the most significant, and to counter the challenges, the deployment of opportunity factors showed an improvement in the performance of the twin spark configuration. Moreover, weaknesses attained the least position, which shows a positive perception for developing the future emissions-compliant engine designs. Finally, implementing a twin spark configuration in a two-stroke engine can play a significant role in enhancing its additional benefits.

Effect of swirl ratio on charge convection, temperature stratification, and combustion in gasoline compression ignition engine

Various low-temperature combustion strategies (namely, homogeneous charge compression ignition, reactivity controlled compression ignition, and partially premixed charge compression ignition) have shown the potential to comply with upcoming and prevailing stringent emissions legislations. Low octane gasoline has emerged as an ideal fuel candidate for premixed charge combustion under diesel-like conditions in gasoline compression ignition (GCI) engines. GCI is an excellent technology to rectify future global energy demand imbalance, because it aims to replace diesel (which is in short supply) with low octane fractions/naphtha (which is in surplus supply) in compression ignition engines. However, this novel combustion concept requires modifications in the conventional design of diesel engines. The combustion chamber shape and in-cylinder flows play a crucial role in charge distribution and temperature stratification. Therefore, understanding the combined effect of combustion chamber geometry and in-cylinder flows is essential for future engine designs. GCI combustion engine simulations for varying swirl ratios (SRs) were performed in CONVERGE CFD software to understand the effect of in-cylinder air motion on the mixture stratification and combustion. A 1/7th sector geometry for a conventional re-entry piston bowl was modeled and then simulated. Two different mechanisms were used for model validation. The results indicated that the large-scale flow structures govern the fuel distribution in the combustion chamber. The charge convection because of increased swirl has a substantial effect on the combustion characteristics of the engine. A distinguished ignition kernel was observed for all test cases. An interfacial region with counter-rotating vortices formed a lean mixture zone, hindering flame propagation and combustion. A lower SR, shallow depth piston, and modifications to avoid flame quenching in the squish zone need to be further investigated to optimize the engine performance.

Fully Coupled Turbojet Engine Computational Fluid Dynamics Simulations and Cycle Analyses Along the Equilibrium Running Line

Abstract This work presents fully coupled computational fluid dynamics (CFD) simulations and thermodynamic cycle analyses of a small-scale turbojet engine at several conditions along the equilibrium running line. The CFD simulations use a single mesh for the entire engine, from the intake to the exhaust, allowing information to travel in all directions. The CFD simulations are performed along the equilibrium running line by using the iterative Secant method to compute the fuel flow rate required to match the compressor and turbine power. The freestream pressure and temperature and shaft angular speed are the only inputs needed for the CFD simulations. To evaluate the consistency of the CFD results with thermodynamic cycle results, outputs from the CFD simulations are prescribed as inputs to the cycle model. This approach enables on-design and off-design cycle calculations to be performed without requiring turbomachinery performance maps. In contrast, traditional off-design cycle analyses require either scaling, calculating, or measuring compressor and turbine maps with boundary condition assumptions. In addition, the CFD simulations and the cycle analyses are compared with measurements of the turbojet engine. The CFD simulations, thermodynamic cycle analyses, and measurements agree in terms of total temperature and pressure at the diffuser–combustor interface, air and fuel mass flow rate, equivalence ratio, and thrust. The developed methods to perform CFD simulations from the intake to the exhaust of the turbojet engine are expected to be useful for guiding the design and development of future small-scale gas turbine engines.

CFD modelling and numerical investigation of a large marine two-stroke dual fuel direct injection engine

ABSTRACT This study aims at developing a CFD model for large marine two-stroke dual fuel engine with gaseous fuel direct injection at high pressure. For the gaseous fuel, the shock tube theory and the pseudo-diameter concept are employed to model the injection, jet penetration and air entrainment processes, whereas its non-premixed combustion is represented by a steady diffusion flamelet model along with a pilot fuel ignition kernel. Following this model validation, a large marine two-stroke dual fuel engine closed cycle is simulated for both the gas and diesel modes at 75% load, and the involved phenomena are comparatively assessed. The derived results demonstrate that the gas mode combustion takes place in lower maximum temperature and leaner conditions compared to the diesel mode, resulting in lower NOx emissions. This study is expected to benefit the development of future engine designs and the engine settings optimisation for reducing emissions and increasing efficiency.

Characteristics of a non-reacting spray from an outwardly opening hollow-cone injector with high-reactivity gasolines

The effects of charge gas temperature, gas pressure, and fuel type on liquid penetration length and cone angle of a hollow-cone spray from an outwardly opening piezoelectric injector was investigated. High-speed diffused back-illumination extinction imaging (DBIEI) was used to perform the measurements in a constant pressure vessel. The conditions studied in this work are relevant to gasoline direct injection (GDI) and gasoline compression ignition (GCI) engine combustion: injection pressure was kept at 120 bar, in-chamber pressure and temperature were varied from 1 bar to 10 bar, and 21 °C to 200 °C, respectively. Experiments were performed with two high-reactivity gasoline fuels, namely high-reactivity gasoline 1 (HRG1) and high-reactivity gasoline 2 (HRG2), which have similar auto-ignition characteristics but substantially different distillation and physical properties. These fuels are candidates to work with future engine designs with a better performance. The motivation here was to understand what physical properties are important in air fuel mixture preparation. Liquid penetration reduces with increasing gas temperature and pressure for both fuels whereas cone angle increases only with increasing gas temperature. At high temperatures, HRG2 yields up to 25% longer liquid penetration length compared to HRG1. For a detailed understanding of effects of fuel properties on liquid penetration, a detailed numerical study was conducted using CONVERGE. By changing a single fuel property at a time, the effects of each fuel physical property was isolated. It was found that density, specific heat, surface tension and heat of vaporization are the most influential physical properties on spray penetration.

Low temperature autoignition of 5-membered ring naphthenes: Effects of substitution

The development and design of future internal combustion engines requires fundamental understanding and the capability to model the autoignition and pollutant formation behavior of petroleum-based and other fuels. Naphthenes are an important constituent of gasoline, and they can comprise larger portions of unconventionally-derived gasoline. There is a lack of data and validated models for 5-membered ring naphthenes. In this work, the autoignition characteristics of cyclopentane, and two of its substituted analogues, methylcyclopentane, and ethylcyclopentane are investigated using a twin-piston rapid compression machine. Each fuel is studied at engine-representative conditions: 20, 50 bar and 700–980 K, with mixtures containing stoichiometric fuel/oxygen ratios at various extents of dilution with inert gases.Negative temperature coefficient (NTC) behavior is observed for cyclopentane, though first-stage ignition and associated low temperature heat release behavior are only evident at temperatures below that for the transition to NTC. Pressure is found to have a larger impact on the reactivity than oxygen dilution, with both effects amplified in the NTC region. The cyclopentane experiments in this study are challenged by the sensitivity of this molecule to non-uniform, or mild ignition phenomena within the NTC region. The addition of saturated sidechains in methyl- and ethylcyclopentane significantly increases the reactivity of the molecules, especially at low temperature and NTC conditions. At the highest temperatures though, there is little difference between the three naphthenes. Typical two-stage ignition behavior is observed across a wide range of temperatures for these alkyl cyclopentanes with no mild ignition observed within the NTC region.A recently developed model for cyclopentane is extended to include reactions for methylcyclopentane, and this is used to simulate the new experiments. The simulation results indicate that low temperature reactivity of cyclopentane is dominated by HO2 elimination of the RO2 species producing cyclopentene, and this inhibits autoignition since it is a very stable molecule. When a methyl group is substituted on the ring, additional RO2 isomerization pathways are available, and these substantially increase the fuel reactivity. HO2 elimination is also important with methylcyclopentane, and this leads to significant production of cyclic olefins which can further react to produce diolefins. These findings are consistent with observations that have been made in other experimental apparatuses.

Heat Transfer in the Core Compressor Under Ice Crystal Icing Conditions

It has been recognized in recent years that high altitude atmospheric ice crystals pose a threat to aircraft engines. Instances of damage, surge, and shutdown have been recorded at altitudes significantly greater than those associated with supercooled water icing. It is believed that solid ice particles can accrete inside the core compressor, although the exact mechanism by which this occurs remains poorly understood. Development of analytical and empirical models of the ice crystal icing phenomenon is necessary for both future engine design and this-generation engine certification. A comprehensive model will require the integration of a number of aerodynamic, thermodynamic, and mechanical components. This paper studies one such component, specifically the thermodynamic and mechanical processes experienced by ice particles impinging on a warm surface. Results are presented from an experimental campaign using a heated and instrumented flat plate. The plate was installed in the Altitude Icing Wind Tunnel (AIWT) at the National Research Council of Canada (NRC). This facility is capable of replicating ice crystal conditions at altitudes up to 9 km and Mach numbers up to 0.55. The heated plate is designed to measure the heat flux from a surface at temperatures representative of the early core compressor, under varying convective and icing heat loads. Heat transfer enhancement was observed to rise approximately linearly with both total water content (TWC) and particle diameter over the ranges tested. A Stokes number greater than unity proved to be a useful parameter in determining whether heat transfer enhancement would occur. A particle energy parameter was used to estimate the likelihood of fragmentation. Results showed that when particles were both ballistic and likely to fragment, heat transfer enhancement was independent of both Mach and Reynolds numbers over the ranges tested.

Numerical modelling of fuel spray formation and collapse from multi-hole injectors under flash-boiling conditions

Flash-boiling of fuel sprays can occur when the fuel enters a metastable superheated state, which is common in direct-injection spark-ignition engines operating at low in-cylinder pressures and/or hot fuel temperatures. The effect of flash-boiling on the resultant spray formation can be both detrimental and advantageous to engine operation, hence numerical modelling capability is essential in future engine optimisation and design. A recently-developed new model by the current authors that can be applied as zero-dimensional boundary condition for multi-hole flash-boiling fuel spray predictions was investigated over a wide range of injection systems, focusing on the model’s ability to quantify in-nozzle phase change effects and automatically predict important global spray characteristics such as spray collapse, droplet recirculation and plume merging within a Lagrangian particle tracking framework. Mesh-type sensitivity was highlighted using a uniform Cartesian and a non-uniform polyhedral mesh. The model was also normalised through a dimensionless parameter for a wide range of single component fuels. The model was validated both qualitatively and, where possible, quantitatively against experimental data. The model’s ability to deal with a wide range of injection configurations and operating conditions was confirmed and a number of limitations are highlighted and discussed with respect to future work.

Maximum efficiencies for internal combustion engines: Thermodynamic limitations

The thermodynamic limitation for the maximum efficiencies of internal combustion engines is an important consideration for the design and development of future engines. Knowing these limits helps direct resources to those areas with the most potential for improvements. Using an engine cycle simulation which includes the first and second laws of thermodynamics, this study has determined the fundamental thermodynamics that are responsible for these limits. This work has considered an automotive engine and has quantified the maximum efficiencies starting with the most ideal conditions. These ideal conditions included no heat losses, no mechanical friction, lean operation, and short burn durations. Then, each of these idealizations is removed in a step-by-step fashion until a configuration that represents current engines is obtained. During this process, a systematic thermodynamic evaluation was completed to determine the fundamental reasons for the limitations of the maximum efficiencies. For the most ideal assumptions, for compression ratios of 20 and 30, the thermal efficiencies were 62.5% and 66.9%, respectively. These limits are largely a result of the combustion irreversibilities. As each of the idealizations is relaxed, the thermal efficiencies continue to decrease. High compression ratios are identified as an important aspect for high-efficiency engines. Cylinder heat transfer was found to be one of the largest impediments to high efficiency. Reducing cylinder heat transfer, however, is difficult and may not result in much direct increases of piston work due to decreases of the ratio of specific heats. Throughout this work, the importance of high values of the ratio of specific heats was identified as important for achieving high thermal efficiencies. Depending on the selection of constraints, different values may be given for the maximum thermal efficiency. These constraints include the allowed values for compression ratio, heat transfer, friction, stoichiometry, cylinder pressure, and pressure rise rate.

Aeroacoustic catastrophes: upstream cusp beaming in Lilley's equation.

The downstream propagation of high-frequency acoustic waves from a point source in a subsonic jet obeying Lilley's equation is well known to be organized around the so-called 'cone of silence', a fold catastrophe across which the amplitude may be modelled uniformly using Airy functions. Here we show that acoustic waves not only unexpectedly propagate upstream, but also are organized at constant distance from the point source around a cusp catastrophe with amplitude modelled locally by the Pearcey function. Furthermore, the cone of silence is revealed to be a cross-section of a swallowtail catastrophe. One consequence of these discoveries is that the peak acoustic field upstream is not only structurally stable but also at a similar level to the known downstream field. The fine structure of the upstream cusp is blurred out by distributions of symmetric acoustic sources, but peak upstream acoustic beaming persists when asymmetries are introduced, from either arrays of discrete point sources or perturbed continuum ring source distributions. These results may pose interesting questions for future novel jet-aircraft engine designs where asymmetric source distributions arise.

Experimental investigations of coaxial injectors in a laboratory-scale rocket combustor

An investigation is performed through experiments of a laboratory-scale optically accessible combustor equipped with a single-element shear coaxial injector. Various optical diagnostics approaches, such as hydroxyl (OH) planar laser-induced fluorescence (OH-PLIF), high-speed imaging and infrared imaging, are simultaneously used to determine the OH radical spatial distribution, flame instantaneous fluctuations, and temperature fields outside the combustor nozzle. This study emphasizes the combustion characteristics and flame stabilizations of two propellant combinations under the same thrust level, including gaseous hydrogen/gaseous oxygen (GH2/GO2) and gaseous methane/gaseous oxygen (GCH4/GO2). Moreover, to validate a pressure-scaling criterion, different pressure conditions are also considered. Based on the results of the high-speed and OH-PLIF images, combustion similarities are evident under different chamber pressures for each propellant couple. The two kinds of flame are seen to be stabilized in the vicinity of the oxidizer injector lip but the anchor region in the GCH4/GH2 cases is found to change dynamically near the lip. The lift-off GCH4/GO2 flame exhibits evident unsteady combustion phenomenon in the combustor. Experimental data indicates that GCH4/GO2 flame stabilization is hard to achieve compared to the GH2/GO2 flame. Furthermore, the GCH4/GO2 flame has a greater heat releasing intensity and gentler reaction zone distribution. This indicates that relative to the GH2/GO2 flame, the GCH4/GO2 flame causes major issues with regard to heat protection of the inner wall in the combustor. Meanwhile, according to the infrared images, the GCH4/GO2 plume has a lower outlet core temperature and larger temperature gradient, which is an advantage for employment in future space engines. This study, identifying preliminary behavior differences between the GH2/GO2 and GCH4/GO2 flames, will be applicable for future engine design.

Effect of dissimilar valve lift on a bi-fuel CNG engine operation

The combustion of spark ignition engines converted to bi-fuel CNG is unstable and proper air and fuel mixing strategy is a concern. Also, CNG fuel causes the coefficient of variation for indicated mean effective pressure (COVimep) higher than 10% which is into the region of unstable combustion. In order to create stable combustion more turbulence is required. This paper studies the valve movement with dissimilar valve lift (DVL) to increase swirl in the engine. The intake valve is the last point of airflow entry into an engine and the modification of the movement can contribute to increase turbulence. Three DVL setting simulated via computational fluid dynamics (CFD) gave improvement in peak pressure by 4% and a 32.2% improvement in flame propagation speed compared to baseline CNG. Engine testing shows that, the engine COVimep improves up to 8.7%, while efficiency improves by 5.7% and BSFC is reduced by 5.4% respectively with the 1 mm DVL at 4000 rpm compared to baseline CNG. The rate of heat release (ROHR) also shows early heat release of the fuel. The novelty is better mileage for future CNG engine design.

Decibel: The Relational Dataset Branching System.

As scientific endeavors and data analysis become increasingly collaborative, there is a need for data management systems that natively support the versioning or branching of datasets to enable concurrent analysis, cleaning, integration, manipulation, or curation of data across teams of individuals. Common practice for sharing and collaborating on datasets involves creating or storing multiple copies of the dataset, one for each stage of analysis, with no provenance information tracking the relationships between these datasets. This results not only in wasted storage, but also makes it challenging to track and integrate modifications made by different users to the same dataset. In this paper, we introduce the Relational Dataset Branching System, Decibel, a new relational storage system with built-in version control designed to address these shortcomings. We present our initial design for Decibel and provide a thorough evaluation of three versioned storage engine designs that focus on efficient query processing with minimal storage overhead. We also develop an exhaustive benchmark to enable the rigorous testing of these and future versioned storage engine designs.

Dual Drive Booster for a Two-Spool Turbofan: Performance Effects and Mechanical Feasibility

A novel two-spool turbofan engine configuration is described which uses a booster powered by both the low an high pressure spools. Design and off-design performance analysis shows the operating characteristics of the configuration, and a mechanical feasibility study of the gearbox is presented. The trends toward ever higher engine overall pressure ratio and bypass ratio have resulted in a combination of higher pressure ratio and lower blade speed in the booster compressor of conventional two-spool turbofans. This combination gives rise to many stages in the booster and/or lower booster efficiency and also a higher degree of off-design mismatch between the core compressors. The current paper describes an engine architecture which aims to alleviate both these issues by powering the booster compressor from both low and high pressure spools through an epicyclic gear system. We have called this engine architecture the dual drive booster. The concept gives the engine designer greater flexibility to optimize component performance and work split, resulting in the potential for lower cruise specific fuel consumption and higher hot-day takeoff thrust capability than current engine configurations. The gear system is described along with the mathematical derivation of the booster rotational speed in terms of LP- and HP-spool speeds. Both the design point and off-design performance modeling have been conducted and comparison is made between a conventional turbofan and a turbofan fitted with the dual drive booster. The results show a significant enhancement in takeoff thrust due to the better speed match of the booster. The paper also describes the results of a preliminary study into the design and mechanical feasibility of the engine architecture and gear system. The presented concept is an alternative to the conventional turbofan and should be considered during the conceptual design of future aircraft engines.

CMAS degradation of EB-PVD TBCs: The effect of basicity

Turbine entry temperatures of aerospace gas turbine engines will need to increase in future engine designs due to a constant desire to improve fuel efficiency and power whilst decreasing emissions which may be environmentally harmful. At present, thermal barrier coatings (TBCs) are employed together with a cooling film to protect engine hardware from the high temperatures seen within the turbine and combustion zones. Airborne particles such as dust, sand and volcanic ash, otherwise termed ‘CMAS’ (calcium–magnesium–alumino-silicates) are ingested into the engine, where at the elevated temperatures, this deposit can melt and induce degradation of the TBC.The columnar, high porosity microstructure of electron-beam physical vapour deposited (EB-PVD) TBCs, typically found on high pressure turbine blades, makes them particularly susceptible to CMAS molten deposit attack. This paper investigates the effect of modifying the chemical composition of molten CMAS deposits on the degradation mechanisms of EB-PVD TBCs. This paper identifies a parameter termed “basicity index” which can be used to evaluate the severity and damage caused by these molten deposits to TBCs. It is believed that the higher temperatures expected to be observed in next generation aero-engines coupled with sand/dust chemistry varying around the world, and then basicity-driven TBC degradation will become more prevalent.

Experimental Determination of Liquefied Petroleum Gas–Gasoline Mixtures Knock Resistance

The results of previous experimental researches showed that great advantages can be achieved, both in terms of fuel consumption and pollutant emissions, in bifuel vehicles by means of the double-fuel combustion, i.e., the simultaneous combustion of gasoline and a gaseous fuel, such as liquefied petroleum gas (LPG) or natural gas (NG). The substantial increase in knock resistance pursued by adding LPG to gasoline, which allowed to maintain an overall stoichiometric proportion with air also at full load, is not documented in the scientific literature and induced the authors to perform a proper experimental campaign. The motor octane number (MON) of LPG–gasoline mixtures has been hence determined on a standard cooperative fuel research (CFR) engine, equipped with a double-fuel injection system in order to realize different proportions between the two fuels and electronically control the overall air–fuels mixture. The results of the measurement show a quadratic dependence of the MON of the mixture as function of the LPG concentration evaluated on a mass basis, with higher increase for the lower LPG content. A good linear relation, instead, has been determined on the basis of the evaluated LPG molar fraction. The simultaneous combustion of LPG and gasoline may become a third operative mode of bifuel vehicles, allowing to optimize fuel economy, performances, and pollutant emissions; turbocharged bifuel engines could strongly take advantage of the knock resistance of the fuels mixture thus adopting high compression ratio (CR) both in pure gas and double-fuel mode, hence maximizing performance and reducing engine size. The two correlations determined in this work, hence, can be useful for the design of future bifuel engines running with knock safe simultaneous combustion of LPG and gasoline.

Experimental Investigation on the Aerodynamics of a Bio-Inspired Flexible Flapping Wing Micro Air Vehicle

An experimental investigation on a 10 cm bio-inspired flexible Flapping-Wing Micro Air Vehicle (FWMAV) was conducted in both hovering and forward-flight conditions with the objective to characterize its aerodynamic performance. The measurements in hovering conditions were performed with the particular objective to explore the effect of different wing configurations (i.e. different aspect ratios and wing flexibilities), whereas forward flight tests in a wind tunnel were carried out to assess the aerodynamic performance of the FWMAV as a function of flow speed, flapping frequency and body angle. The cyclic variation of forces (lift and thrust) generated as a result of the wing flapping was captured by means of a high-resolution force sensor, in combination with high-speed imaging to track the wing motion. Results of measurements in hover show that the flapping frequency, aspect ratio and wing flexibility have a crucial impact on the efficiency and the force generation during the flapping cycle. An estimated flight envelop for the MAV's operation is defined from the data obtained in the wind tunnel measurements. Furthermore, additional tests on several brushless DC motors provide a feasible option in future engine selection and design.

High-Speed Characterization of ECN Spray A Using Various Diagnostic Techniques

Diesel spray experimentation at controlled high-temperature and high-pressure conditions is intended to provide a more fundamental understanding of diesel combustion than can be achieved in engine experiments. This level of understanding is needed to develop the high-fidelity multi-scale CFD models that will be used to optimize future engine designs. Several spray chamber facilities capable of high-temperature, igh-pressure conditions typical of engine combustion have been developed, but because of the uniqueness of each facility, there are uncertainties about their operation. The Engine Combustion Network (ECN) is a worldwide group of institutions using combustion vessels, whose aim is to advance the state of spray and combustion knowledge at engine-relevant conditions. A key activity is the use of spray chamber facilities operated at specific target conditions in order to leverage research capabilities and advanced diagnostics of all ECN participants. The first target condition, called “Spray A”, has been defined with detailed ambient and injector conditions. For this paper, we describe results from the constant-volume pre-burn vessel at Eindhoven University of Technology. The executed measurements include a wide range of diagnostics to characterize “spray A” in reacting and non-reacting conditions in great detail. Observations of spray penetration, ignition, liquid length and flame lift-off location by using several high-speed imaging diagnostics are discussed and compared with other ECN participating institutes. Comparison Spray A data from the other participating institutes, as it was presented during the 2nd ECN workshop is gathered from the ECN website database [1]. It can be concluded that the obtained results from the standardized ECN spray diagnostics, show satisfactory similarity, despite of the challenge to reach similar boundary conditions (ambient and injector) in each of the unique facilities. The differences in results are within the measurement deviation and uncertainty or can be explained by the usage of (slightly) different injectors. Combining the results of the different measurement techniques provides an overall (time resolved) overview where the different phases of fuel injection are directly linked and summarized. The presented overview provides a direct input for (CFD) modeling validation.

Insights into Cold-Start DISI Combustion in an Optical Engine Operating at −7°C

Particulate Matter (PM) emissions reduction is an imminent challenge for Direct Injection Spark Ignition (DISI) engine designers due to the introduction of Particulate Number (PN) standards in the proposed Euro 6 emissions legislation aimed at delivering the next phase of air quality improvements. An understanding of how the formation of combustion derived nanoparticulates in engines is affected by the engine operating temperature is important for air quality improvement and will influence future engine design and control strategies. This investigation has examined the effect on combustion and PM formation when reducing the engine operating temperature to -7°C. A DISI single-cylinder optical research engine was modified to simulate a range of operating temperatures down to the proposed -7°C. A high-speed 9 kHz optical investigation of the in-cylinder combustion and fuel spray along with incylinder pressure measurements was completed with the engine motored and fired at 1500 rpm during homogeneous and stoichiometric combustion conditions. Results show striking differences between the flame growth structures at various operating conditions with the notable presence of significant fuel-rich regions which are understood to be prominent areas of PM formation. Measured engine performance parameters such as Indicated Mean Effective Pressure (IMEP) and Mass Fraction Burned (MFB) times correlated with the observed differences in combustion characteristics and flame growth speed. Flash boiling of the fuel spray was present in the fully heated engine case and significantly reduced the penetration of the spray plume and the likelihood of piston crown and cylinder liner impingement. A clear link was shown between operating temperature, engine performance and in-cylinder combustion parameters which contribute to the formation of PM. Copyright © 2013 SAE International.