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Technical Paper

Bowl Geometry Effects on Turbulent Flow Structure in a Direct Injection Diesel Engine

2018-09-10
2018-01-1794
Diesel piston bowl geometry can affect turbulent mixing and therefore it impacts heat-release rates, thermal efficiency, and soot emissions. The focus of this work is on the effects of bowl geometry and injection timing on turbulent flow structure. This computational study compares engine behavior with two pistons representing competing approaches to combustion chamber design: a conventional, re-entrant piston bowl and a stepped-lip piston bowl. Three-dimensional computational fluid dynamics (CFD) simulations are performed for a part-load, conventional diesel combustion operating point with a pilot-main injection strategy under non-combusting conditions. Two injection timings are simulated based on experimental findings: an injection timing for which the stepped-lip piston enables significant efficiency and emissions benefits, and an injection timing with diminished benefits compared to the conventional, re-entrant piston.
Technical Paper

Effect of Butanol Addition on Performance, Combustion Stability and Nano-Particle Emissions of a Conventional Diesel Engine

2018-09-10
2018-01-1795
This study presents the experimental investigation of performance, combustion, gaseous and nano-particle emission characteristics of conventional compression ignition (CI) engine fueled with neat diesel and butanol/diesel blends. The experiments were conducted for neat diesel, 10%, 20% and 30% butanol/diesel blend on the volume basis at different engine loads. Combustion characteristics were investigated on the basis of in-cylinder pressure measurement and heat release analysis. The in-cylinder combustion pressure traces were recorded for 2000 consecutive engine combustion cycles for computation of heat release and different combustion parameters. Combustion stability analysis is conducted by analyzing the coefficient of variation of in indicated mean effective pressure (IMEP) and total heat release (THR). Wavelet analysis is also used for analyzing the temporal variations in IMEP data series.
Technical Paper

Investigation into the Optimized Heat Release Rate and Corresponding Variation of In-Cylinder Specific Heat Ratio for the Improvement in Thermal Efficiency by Utilizing Two-Zone Combustion Model Analysis

2018-09-10
2018-01-1796
Improvement in heat loss could be an important factor to increase the brake thermal efficiency (BTE) of an internal combustion engine; however, the heat energy saved isn’t all converted to brake work. Theoretically, to increase the conversion efficiency of heat energy into indicated work, the compression (or expansion) ratio and specific heat ratio (γ) are important. Nevertheless, γ has not been well-studied thus far, since it can’t be easily controlled. This study utilized a two-zone model to calculate the time-resolved γ and local excess air ratio of the burned gas (λb), which varied with the heat release rate. The two-zone combustion model, in which the cylinder volume is simply separated into burned and unburned zones to simulate the overall diesel combustion phenomena, was developed to investigate the current status of heterogeneous (diesel) combustion compared to ideal homogeneous combustion.
Technical Paper

Analyzing Factors Affecting Gross Indicated Efficiency When Inlet Temperature Is Changed

2018-09-10
2018-01-1780
Observations from engine experiments indicates that the gross indicated efficiency (GIE) increases when the inlet temperature (Tinlet) is lowered. The change in Tinlet affects several important factors, such as the heat release profile (affecting heat and exhaust losses), working fluid properties, combustion efficiency and heat transfer losses. These factors all individually contributes to the resulting change in GIE. However, due to their strong dependency to temperature it is not possible to quantify the contribution from each of these parameters individually. Therefore, a simulation model in GT-power has been created and calibrated to the performed engine experiments. With simulations the temperature dependency can be separated and it becomes possible to evaluate the contribution to GIE from each factor individually. The simulation results indicate that the specific heats of the working medium are the largest contributor.
Technical Paper

Natural Flame Luminosity and Emission Spectra of Diesel Spray Flame under Oxygen-Enriched Condition in an Optical Constant Volume Vessel

2018-09-10
2018-01-1781
The application of oxygen-enriched or oxy-fuel combustion coupled with carbon capture and storage technology has zero carbon dioxide emission potential in the boiler and gas turbine of the power plant. However, the oxygen-enriched combustion with high oxygen level has few studies in internal combustion engines. The fundamental issues and challenges of high oxygen level are the great differences in the physical properties and chemical effects compared with the combustion in air condition. As a consequence, the diesel spray combustion characteristics at high oxygen level were investigated in an optical constant volume vessel. The oxygen volume fraction of tested gas was from 21% to 70%, buffered with argon. The high-speed color camera was used to record the natural flame luminosity.
Technical Paper

Experimental Investigation of Flame-Wall-Impingement and Near-Wall Combustion on the Piston Temperature of a Diesel Engine Using Instantaneous Surface Temperature Measurements

2018-09-10
2018-01-1782
The heat transfer process in a reciprocating engine is dominated by forced convection, which is drastically affected by mean flow, turbulence, flame propagation and its impingement on the combustion chamber walls. All these effects contribute to a transient heat flux, resulting in a fast-changing temporal and spatial temperature distribution at the surface of the combustion chamber walls. To quantify these changes in combustion chamber surface temperature, surface temperature measurements on the piston of a single cylinder diesel engine were taken. Therefore, thirteen fast-response thermocouples were installed in the piston surface. A wireless microwave telemetry system was used for data transmission out of the moving piston. A wide range of parameter studies were performed to determine the varying influences on the surface temperature of the piston.
Technical Paper

An Experimental Investigation on Spray Mixing and Combustion Characteristics for Spray C/D Nozzles in a Constant Pressure Vessel

2018-09-10
2018-01-1783
The Engine Combustion Network (ECN) is a coordinate effort from research partners from all over the world which aims at creating a large experimental database to validate CFD calculations. Two injectors from ECN, namely Spray C and D, have been compared in a constant pressure flow vessel, which enables a field of view of more than 100 mm. Both nozzles have been designed with similar flow metrics, with Spray D having a convergent hole shape and Spray C a cylindrical one, the latter being therefore more prone to cavitation. Although the focus of the study is on reacting conditions, some inert cases have also been measured. High speed schlieren imaging, OH* chemiluminescence visualization and head-on broadband luminosity have been used as combustion diagnostics to evaluate ignition delay, lift off length and reacting tip penetration. Parametric variations include ambient temperature, oxygen content and injection pressure variations.
Technical Paper

A Modeling Study on the Influence of Aromatic Fluorescence Tracers on Compression Ignition Engine Operation

2018-09-10
2018-01-1784
Aromatic substances, which are added to the fuel as fluorescing tracers, are in widespread use as a means of investigating mixing and reaction processes in IC engines by laser-based visualization techniques. The fuel/tracer/air mixture may differ from the pure fuel/air mixture in its chemical and its physical properties, and both aspects can be equally relevant for engine operation. They may, furthermore, interact due to the dependence of chemical reaction on physical conditions. In this paper, we study the overall influence of toluene as an exemplary aromatic tracer on engine performance by numerical modeling. The used model features a semi-detailed treatment of chemical reactions for both the fuel and the tracer, as well as their mutual chemical kinetics interactions. The dependence of engine performance parameters like auto-ignition timing and maximum pressures on these parameters is investigated by performing a large set of parametric simulations.
Technical Paper

Performance and Exhaust Emissions Analysis of a Diesel Engine Using Oxygen-Enriched Air

2018-09-10
2018-01-1785
Oxygen enriched air (EA) is a well known industrial mixture in which the content of oxygen is higher respect the atmospheric one, in the range 22-35%. Oxygen EA can be obtained by desorption from water, taking advantage of the higher oxygen solubility in water compared to the nitrogen one, since the Henry constants of this two gases are different. The production of EA by this new approach was already studied by experimental runs and theoretical considerations. New results using salt water are reported. EA promoted combustion is considered as one of the most interesting technologies to improve the performance in diesel engines and to simultaneously control and reduce pollution. This paper explores, by means of 3-dimensional computational fluid dynamics simulations, the effects of EA on the performance and exhaust emissions of a high-speed direct-injection diesel engine.
Technical Paper

Study of Swirl Ratio on Mixture Preparation with a Swirl Control Valve in a Diesel Engine

2018-09-10
2018-01-1790
Downsizing as a main-stream technology was widely used for design of future diesel engines in order to meet the increasingly stringent demands of emissions regulation and reduction of CO2 production. Design of intake system faces a considerable challenge accordingly. Discharge coefficient and swirl ratio as two main factors of intake port design have been widely investigated by researchers. However, these two parameters indicate a trade-off relationship. Therefore, it is difficult for a classical intake system to achieve a good balance between sufficient air charge and decent air-fuel radial mixing quality. A 1 L twin-intake-port single-cylinder diesel engine was studied in this paper. A swirl control valve designed to adjust the effective flow area of the filling port, was installed between the intake manifold and the intake filling port in order to achieve variation of swirl ratio. And there is no control valve for the intake spiral port.
Technical Paper

Auto-ignition Characteristics of Lubricant Droplets under Hot Co-Flow Atmosphere

2018-09-10
2018-01-1807
It has been revealed by researches that lubricant properties have a great effect on the low-speed pre-ignition (LSPI) frequency in downsizing turbocharged direct-injection engines which are developed for better fuel economy. Droplets of lubricant or lubricant-gasoline mixture are considered to be the potential pre-ignition sources. Those droplets fly into the combustion chamber and ignite the gasoline-air mixture. To study lubricant droplets fundamentally, a novel set of droplet auto-ignition system is designed based on a Dibble Burner for this experiment. Influences of metallic additive contents, viscosities, lubricant diluted with gasoline and waste lubricant on the ignition delay of droplets are investigated by testing 12 groups of lubricants or lubricant-gasoline mixture. The equivalent diameter of each droplet generated by micro-syringes is around 2.1 mm. The co-flow temperature varies from 1123 K to 1223 K, and the experiments are carried out at atmospheric pressure.
Technical Paper

Prediction of Lubricant Performance in an EHL Valvetrain Simulation Using an Equation of State and Detailed Rheology Characterization Approach

2018-09-10
2018-01-1806
With the continued CO2 reduction challenges for automotive engines, it becomes necessary to minimize friction losses. Many studies in the past have used generic equations of state to account for changes in density, neglecting the compressibility difference between fluids, whereas this study used accurately measured equations of state, for each of the oils. Density change is generally only accounted for in terms of mass conservation, an effort has been made here to develop a link between viscosity characteristics and density, by separating molecular density and molecular interaction contributions rather than using an all-encompassing pressure-viscosity coefficient. Several studies have not accounted for all physical aspects acting within an elasto-hydrodynamic contact, because of the difficulties associated with model convergence.
Technical Paper

Study of Interaction of N-Methyl Aniline Octane Booster on Lubricating Oil

2018-09-10
2018-01-1809
The impact of N-Methyl Aniline (NMA) octane booster on lubricating oil has previously been studied and the main findings were reported in SAE paper 2016-01-2273. Increased sludge formation had been observed in modified ACEA black sludge testing when NMA was added to the fuel but there was very limited viscosity increase, which did not corroborate the trend evidenced on modified CEC L-109 oxidation testing where significant viscosity increase was noted when NMA was added to the oil and fuel mixture. Accordingly, modified black sludge tests have been run with and without NMA added to the oil sump at the beginning of the test to better match modified L-109 oxidation bench test conditions. Results showed the same trend in terms of viscosity increase between the modified L-109 oxidation bench test and black sludge test.
Technical Paper

Development of a Standardized Test to Evaluate the Effect of Gasoline Engine Oil on the Occurrence of Low Speed Pre-Ignition - The Sequence IX Test

2018-09-10
2018-01-1808
The study described in this paper covers the development of the Sequence IX Low Speed Pre-Ignition (LSPI) test for the new engine oil category, ILSAC GF-6. The purpose of the Sequence IX test is to evaluate a lubricant’s ability to protect against LSPI events which are prevalent when operating a highly boosted/downsized gasoline direct-injected engine. LSPI is characterized as a combustion event that starts before ignition spark, typically followed by excessive in-cylinder pressures and heavy knock, which can cause severe engine damage and failure. Industry research has shown that oil formulation can contribute to the frequency of LSPI activity. The Sequence IX test was developed using a turbocharged gasoline direct-injected 2.0 liter Ford Ecoboost engine with dual independent variable cam timing. The engine was modified with in-cylinder pressure sensors and a high-resolution crank angle encoder to characterize individual engine combustion cycles and identify potential LSPI events.
Technical Paper

Variation in System Performance while Sorting DEF Heating Hardware Options

2018-09-10
2018-01-1813
The desire to reduce NOx at low ambient temperatures drives the use of heating methods to make DEF available by thawing the solution in the tank. Methods to validate modelling used to design hardware options require testing to gauge the accuracy of the prediction. Using a climatic chassis dynamometer (CCD) to demonstrate the guidance procedure set by the Environmental Protection Agency (EPA) is expensive and time consuming. A method of utilizing a flow controlled cooling supply combined with a standard cold chamber is described as a precursor to running the demonstration in the CCD. Testing multiple quantities of design iterations produced unexpected variation in the results. The sources of the variation and modifications taken to minimize them are discussed and presented. Test to test control of coolant flow, coolant temperature, and specific chamber temperature inconsistencies were found to be critically important to a successful effort.
Technical Paper

Investigation of Oil Sources in the Combustion Chamber of Direct Injection Gasoline Engines

2018-09-10
2018-01-1811
To reduce hydrocarbon and particle emissions as well as irregular combustion phenomena, the identification and quantification of possible oil sources in the combustion chamber of the direct injection gasoline engine are of main interest. The aim of this research activity is to fundamentally investigate the formation of locally increased lubricating oil concentration in the combustion chamber. For this purpose, the oil sources are considered separately from each other and divided into two groups - piston/compression ring and lubricating film on the liner. The associated oil emissions and their influence on the engine combustion process are the core of the investigations.
Technical Paper

NH3 Sensor Measurements in Different Engine Applications

2018-09-10
2018-01-1814
In this study the exhaust gas ammonia (NH3) concentrations from different exhaust sources were measured with an ammonia sensor. The aim of the study was to verify whether an NH3 sensor has the potential to be used for monitoring and control purposes for SCR systems. Measurements were performed in laboratory and field conditions and comparison was made between Fourier Transform Infrared (FTIR) and Laser Diode Spectrometer (LDS) measurement techniques. With heavy-duty vehicles, a comparison between an LDS, FTIR and NH3 sensor was performed on a heavy-duty chassis dynamometer. Measurements were performed at steady speeds using a World Harmonized Vehicle Cycle (WHVC) and Braunschweig test cycles. The urea injection rate for the SCR system was varied to generate different ammonia levels in the exhaust gas. NH3 measurements with FTIR and NH3 sensor were performed on large cruise ships using heavy fuel oil (HFO) and marine gas oil (MGO) as fuels.
Technical Paper

Polycyclic Aromatic Hydrocarbons in Diesel Engine Exhaust Both with and without Aftertreatment

2018-09-10
2018-01-1812
Since the conception of the internal combustion engine, smoky and ill-smelling exhaust was prevalent. Over the last century, significant improvements have been made in improving combustion and in treating the exhaust to reduce these effects. One group of compounds typically found in exhaust, polycyclic aromatic hydrocarbons (PAH), usually occurs at very low concentrations in diesel engine exhaust. Some of these compounds are considered carcinogenic, and most are considered hazardous air pollutants (HAP). Many methods have been developed for sampling, handling, and analyzing PAH. For this study, an improved method for dilute exhaust sampling was selected for sampling the PAH in diesel engine exhaust. This sampling method was used during transient engine operation both with and without aftertreatment to show the effect of aftertreatment.
Technical Paper

Compression Ignition of Low Octane Gasoline under Partially Premixed Combustion Mode

2018-09-10
2018-01-1797
Partially premixed combustion (PPC) is an operating mode that lies between the conventional compression ignition (CI) mode and homogeneous charge compression ignition (HCCI) mode. The combustion in this mixed mode is complex as it is neither diffusion-controlled (CI mode) nor governed solely by chemical kinetics (HCCI mode). In this study, CFD simulations were performed to evaluate flame index, which distinguishes between zones having a premixed flame and non-premixed flame. Experiments performed in the optical engine supplied data to validate the model. In order to realize PPC, the start of injection (SOI) was fixed at −40 CAD (aTDC) so that a required ignition delay is created to premix air/fuel mixture. The reference operating point was selected to be with 3 bar IMEP and 1200 rpm. Naphtha with a RON of 77 and its corresponding PRF surrogate were tested. The simulations captured the general trends observed in the experiments well.
Technical Paper

Effect of Temperature-Pressure Time History on Auto-Ignition Delay of Air-Fuel Mixture

2018-09-10
2018-01-1799
When the compression ratio of the spark ignition engine is set high as a method of improving the fuel efficiency of passenger cars, it is often combined with the direct fuel injection system for knock mitigation. In port injection, there are also situations where the fuel is guided into the cylinder while the vaporization is insufficient, especially at the cold start. If the fuel is introduced into the cylinder in a liquid state, the temperature in the cylinder will change due to sensible heat and latent heat of the fuel during vaporization. Further, if the fuel is unevenly distributed in the cylinder, the effect of the specific heat is added, and the local temperature difference is expanded through the compression process. In this research, an experiment was conducted using a rapid compression machine for the purpose of discussing the effect of the temperature-pressure time history of fuel on ignition delay time.
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