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Technical Paper

Simulation Study on Implementation of Oxy-fuel Combustion for a Practical GDI Engine

2021-04-06
2021-01-0380
As the impacts of global warming have become increasingly severe, Oxy-Fuel Combustion (OFC) has been widely considered as a promising solution for Carbon Capture and Storage (CCS) to reduce Carbon Dioxide (CO2) to achieve net-zero emissions. In this study, one-dimensional simulation with GT-Power software was carried out to study the implementation of OFC on a practical turbocharged 4-cylinder Gasoline Direct Injection (GDI) engine. The results demonstrated that the brake power of OFC has a noticeable decline compared to that of Conventional Air-fuel Combustion (CAC) with fixed consumption of fuel and oxygen. Under the OFC mode, in order to restore the equivalent power with CAC, various parameters including ignition timing, intake temperature, intake components, engine compression ratio and water injection strategy, were thoroughly discussed and analysed. The brake power has grown continuously as ignition timing advances from -18 CA ATDC to -38 CA ATDC.
Technical Paper

Numerical Parametric Study of a Six-Stroke Gasoline Compression Ignition (6S-GCI) Engine Combustion - Part III

2021-04-06
2021-01-0401
The aim of this paper is to computationally investigate the combustion behavior and energy recovery processes of a six-stroke gasoline compression ignition (6S-GCI) engine that employs a continuously variable valve duration (CVVD) technique, under highly diluted, low-temperature combustion (LTC) conditions. The effects of variation of parameters concerning injection spray targeting (number of fuel injector holes, injector nozzle size, and spray included angle) and combustion chamber geometry (piston bowl design) are analyzed using an in-house 3D-CFD code coupled with high-fidelity physical sub-models with the Chemkin library in conjunction with a skeletal chemical kinetics mechanism for a 14-component gasoline surrogate fuel.
Technical Paper

An Automated Workflow for Efficient Conjugate Heat Transfer Analysis of a Diesel Engine

2021-04-06
2021-01-0402
The internal combustion engine’s performance is affected by in-cylinder combustion processes and heat transfer rates through the combustion chamber walls. Hot spots may affect the reliability and durability of the engine components. Design of efficient and effective coolant systems requires accurate accounting of the heat fluxes into and out of the solid parts during the engine operation. The need to assess the engine’s performance early in the design process has motivated the use of a computational approach to predict such data. A more accurate representation of the engine’s operation is obtained by coupling the thermal, flow, and combustion analysis of the various components, such as the combustion chamber, ports, engine block, and its cooling system. Typically, a stand-alone CFD simulation does not capture the complex nature of the problem, and the manual transfer of data between multiple analyses may lead to an onerous or error-prone workflow requiring multiple user interventions.
Technical Paper

Cold Flow Simulation of a Dual-Fuel Engine for Diesel-Natural Gas and Diesel-Methanol Fueling Conditions

2021-04-06
2021-01-0411
In this work, the possibility to perform a cold-flow simulation as a way to improve the accuracy of the starting conditions for a combustion simulation is examined. Specifically, a dual-fuel marine engine running on methanol/diesel and natural gas/diesel fueling conditions is investigated. Dual-fuel engines can provide a short-term solution to cope with the more stringent emission legislations in the maritime sector. Both natural gas and methanol appear to be interesting alternative fuels that can be used as main fuel in these dual-fuel engines. Nevertheless, it is observed that combustion problems occur at part load using these alternative fuels. Therefore, different methods to increase the combustion efficiency at part load are investigated. Numerical simulations prove to be very suitable hereto, as they are an efficient way to study the effect of different parameters on the combustion characteristics.
Technical Paper

Hardware-in-the-Loop Based Virtual Emission Calibration of Gasoline Engines

2021-04-06
2021-01-0417
In the field of gasoline powertrain calibration, the challenges are growing due to ever shorter time-to-market requirements and a simultaneous increase in powertrain complexity. In addition, the great variety of vehicle variants requires an increasing number of prototypes for calibration and validation tasks within the framework of the current Real Driving Emissions (RDE) regulations and the expected post EU6 emission standards. Hardware-in-the-Loop (HiL) simulations have been introduced successfully to support the calibration tasks in parallel to the conventional vehicle de-velopment activities. The HiL approach enables a more reliable compliance with emission limits and improves the quality of calibrations while reducing the number of prototype vehicles, test resources and thus overall development costs.
Technical Paper

Determination of Efficiency Losses in Entry Ignition Engines

2021-04-06
2021-01-0441
In 2020, Peter Cheeseman (SAE Paper 2020-01-1314) introduced Entry Ignition (EI) as a potential engine combustion process to rival traditional Spark Ignition (SI) and Compression Ignition (CI). The EI process premixes fuel with compressed air, which then enters a hot cylinder at top dead center, autoigniting upon entry. The original proposed concept for an engine separates the compression and expansion processes allowing for it to be modeled as a 2-stroke Brayton cycle. Theoretically, an EI engine allows for higher compression ratios than SI engines with less emissions than CI engines. However, the original EI engine analysis made several assumptions that merit further investigation. First, the original analysis did not look at the in-cylinder temperatures to determine if autoignition is actually possible in the cylinder, which had just completed its exhaust process.
Technical Paper

Pre-ignition detection and damage mitigation in a Spark-Ignited Engine

2021-04-06
2021-01-0437
Pre-ignition remains a major bottleneck to further downsizing and improved efficiency of modern turbocharged spark-ignited engines. Pre-ignition may lead to high peak pressures and pressure oscillations, known as super-knock which can lead to sudden and permanent hardware damage to the engine. Over the years, numerous researchers have tried to understand the source of such stochastic phenomenon and concluded that there is a role of lubricant additives, of deposits, of gasoline properties, and of hot surfaces in triggering pre-ignition. No single source has been identified; and the research continues. Here, we take a different approach, to mitigating engine damage by detecting pre-ignition early enough to trigger an evasive action. Such evasive action may potentially suppress knock intensity, thereby saving the engine from any permanent damage.
Technical Paper

Controls and Hardware Development of mDSF Technology for Cost-Effective Emissions Reduction

2021-04-06
2021-01-0446
mDSF is a novel cylinder deactivation technology developed at Tula Technology, which combines the torque control of Dynamic Skip Fire (DSF) with Miller cycle engines to optimize fuel efficiency at minimal cost. mDSF employs a valvetrain with variable valve lift plus deactivation and novel control algorithms founded on Tula’s proven DSF technology. This allows cylinders to dynamically alternate among 3 potential states designated as: Hi Fire, Lo Fire, and Skip (deactivation). The Lo Fire state is achieved through an aggressive Miller cycle with Early Intake Valve Closing (EIVC). The three operating states in mDSF can be used to simultaneously optimize engine efficiency and driveline vibrations. Acceleration performance is retained using the all-cylinder, Hi Fire mode. The most cost-effective valvetrain solution for mDSF is comprised of asymmetric intake valve lifts and/or ports, with one high-flow power charging port and one high-efficiency Miller port.
Technical Paper

PWI and DWI Systems in Modern GDI Engines: Optimization and Comparison Part II: Reacting Flow Analysis

2021-04-06
2021-01-0454
In the current scenario characterized by continuous reduction of the allowed limits of mean engine-out emissions over the test-cycles together with the necessity of limiting the local peaks too, which will lead in the next future to the adoption of stoichiometric mixtures at full load conditions, water injection is one of the exploited technologies. At full power, at stoichiometric conditions, water injection is thought to help contributing towards more efficient engines, because its anti-knock attitude in S.I. engine applications. To perform a rapid optimization of the main parameters involved by the water injection process, it is necessary to have reliable CFD methodologies capable of capturing the most important phenomena: indeed, it must be considered that the injection of water changes both the thermodynamic (due to the temperature reduction) and the chemical behavior of the mixture.
Technical Paper

A novel piston insulation technique to simultaneously improve both heat loss and thermal efficiency for diesel engines

2021-04-06
2021-01-0453
Cooling loss reduction is the most essential for further improvement in thermal efficiency to achieve future CO2 emissions target combined with the combustion improvement techniques. Although many studies on heat insulation for diesel engines have been proposed the thin ceramics coating with very low thermal conductivity and low heat capacitance materials on the wall, very little cooling loss reductions, or sometimes rather increased cooling loss were observed. In our previous study, it was confirmed at part load conditions that a forged steel piston applying thin thermal spray coating with yttria stabilized zirconia (8YSZ) on the oil cooling side aiming to increase in cavity surface temperature has a significant potential to improve both the thermal efficiency and the cooling loss. However, this insulation technique is not an essential measure since thermal efficiency in the high load conditions was deteriorated from the baseline.
Technical Paper

The effects of flash boiling and high-energy ignition technologies on combustion process of ethanol-gasoline blends under cold operating conditions

2021-04-06
2021-01-0472
To alleviate the shortage of petroleum resources and the air pollution caused by the burning of fossil fuels, the development of renewable fuels has attracted widespread attention. Among the various renewable fuels, ethanol can be produced from biomass and does not require much modification when applied to practical engines, so it has been widely used. However, ethanol fuel has a higher latent heat value of vaporization than gasoline, it is difficult to evaporate and atomize under cold start conditions. Besides, the catalyst has not reached the conversion temperature at this time, resulting in lower conversion efficiency. These factors all lead to higher pollutant emission levels in ethanol-gasoline blends. To solve the above problems, this research used visualization techniques to compare the effects of flash boiling and high-energy ignition technologies on the in-cylinder combustion process and pollutant emission of ethanol-gasoline blends fuel.
Technical Paper

Experimental and Modeling Study of Spark Plug Electrode Heat Transfer and Thermal Energy Deposition

2021-04-06
2021-01-0480
Spark plug electrode heat transfer and its relationship with the thermal energy deposition from the spark plasma to the gas in the spark gap was studied under quiescent non-combusting conditions. The thermal energy deposition to the gas (N2) was measured with a spark plug calorimeter as a function of pressure, up to 30 bar. The measurements were carried out for two gap distances of 0.3 mm and 0.9 mm, for three nominally identical spark plugs having different electrode surface area and surface thermal conductivity. The unmodified baseline spark plug had a nickel center electrode (cathode) 2.0 mm in diameter, the first modified spark plug had both the ground and center electrodes shaved to a diameter of approximately 0.5 mm, the second modified spark plug had copper inserts bonded to both electrodes. The experimental results were compared with multi-dimensional simulations of the conjugate heat transfer to the gas and to the metal electrodes, conducted using Converge CFD.
Technical Paper

Effects of Multiple Injectors on Spray Characteristics and Efficiency in Internal Combustion Engines

2021-04-06
2021-01-0501
High-pressure internal combustion engines show promises in high efficiencies, but a proper injection strategy to minimize heat losses and pollutant emissions remain a challenge. Previous studies have concluded that two injectors, placed at the piston bowl's rim, simultaneously improve the mixing and reduce the heat losses. The two-injector improves air utilization while keeping hot zones away from the cylinder walls. This study investigates how the multiple-injector concept delivers even higher efficiency by providing additional control of spray -and injection angles. Three-dimensional Reynolds-averaged Navier-Stokes simulations examined several umbrella angles, spray-to-spray angles, and injection orientations by comparing the two-injector cases with a reference one-injector case.
Technical Paper

Effect of intake hydrogenation coupled with intake humidification on combustion and emissions of marine diesel engine

2021-04-06
2021-01-0502
In this paper, the commercial software AVL-Fire was used to establish a three-dimensional numerical model of a four-cylinder turbocharged intercooled marine diesel engine. The influence of intake hydrogenation coupled with intake humidification on the combustion and emission performance of the engine at 1350, part load was studied, and the method to optimize the engine performance was explored. In this study, micro hydrogen (mass ratio of hydrogen to diesel is 1.4%) is injected into the intake port of diesel engine as the activator of in cylinder combustion. On the premise of convenient transportation and carrying, and without significant increase of economic cost, the combustion process in cylinder can be optimized, the combustion speed of diesel can be accelerated, the indicated fuel consumption rate of diesel can be reduced by about 2%, and the soot emission can be reduced by about 6%, so higher thermal efficiency can be obtained for diesel engines through intake hydrogenation.
Technical Paper

Improved Method for Studying MCCI Flame Interactions with an Engine Combustion Chamber

2021-04-06
2021-01-0507
An improved method for studying Mixing Controlled Compression Ignition (MCCI) flame interactions with an engine combustion chamber has been developed. It is implemented in a constant pressure vessel, which contains a portion of a piston, and a portion of a cylinder head, where the cylinder head is a transparent fused silica window. This method allows for fuel jets/flames to be imaged from two orthogonal directions. The piston and cylinder head can be adjusted to emulate piston positions from TDC to approximately 15mm away from TDC. The design allows for pistons from engine bore sizes up to approximately 175mm to be studied and spray angles from 120°-180°. In this study, the piston was made as an extruded piston bowl profile, where the length of the extrusion approximated the arc length between two neighboring jets. Four high speed cameras and two photodiodes were used to capture light emissions.
Technical Paper

A Comparison Study on the Performance of the Multi-stroke Cycle SI Engine under Low Load

2021-04-06
2021-01-0530
Pumping Mean Effective Pressure(PMEP) is the main factor limiting the improvement of thermal efficiency in a spark-ignition(SI) engine under low load. One of the ways to reduce the pumping loss under low load is to use Cylinder DeActivation(CDA). The CDA aims at reducing the firing density(FD) of the SI engine under low load operation and increasing the mass of air-fuel mixture within one cycle in one cylinder to reduce the throttling effect and further reducing the PMEP. The multi-stroke cycles can also reduce the firing density of the SI engine after some certain reasonable design, which is feasible to improve the thermal efficiency of the engine under low load in theory. The research was carried out on a calibrated four-cylinder SI engine simulation platform. The thermal efficiency improvements of the 6-stroke cycle and 8-stroke cycle to the engine performance were studied compared with the traditional 4-stroke cycle under low load conditions.
Technical Paper

Dilute Combustion Control Using Spiking Neural Networks

2021-04-06
2021-01-0534
Dilute combustion with exhaust gas recirculation (EGR) in spark-ignition engines presents a cost-effective method for achieving higher levels of engine efficiency. At high levels of EGR, however, cycle-to-cycle variability (CCV) of the combustion process is exacerbated by sporadic occurrences of misfires and partial burns. Previous studies have shown that temporal deterministic patterns emerge as such conditions and certain combustion cycles have a significant influence over future events. Due to the complexity of the combustion process and the nature of CCV, harnessing all the deterministic information for control purposes has remained challenging even with physics-based 0-D, 1-D, and high fidelity computational fluid dynamics (CFD) models. In this study, we present a data-driven approach to optimize the combustion process by controlling CCV adjusting the cycle-to-cycle fuel injection quantity.
Technical Paper

Investigation on the ignition properties of 1-propanol and 1-butanol under fuel-lean conditions

2021-04-06
2021-01-0564
To mitigate the global warming and to develop sustainable transportation, investigations on combustion properties of carbon neutral fuels i.e., electro-fuels and bio-fuels such as propanol and butanol are essential. In the past, there were very limited researches included the fuel-lean combustion of those fuels which is however a trend to reduce the NOx emissions and therefore the literature chemical kinetic mechanisms must be validated against the fuel-lean ignitions. Ignition delay time (IDT) is one key parameter for combustion properties and can be used for the validation of chemical kinetic mechanisms. IDTs of diluted 1-propanol and 1-butanol mixtures (90% bath gas (Ar+N2)) were therefore conducted in a rapid compression machine (RCM), which covers the working conditions of internal combustion engines.
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