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Combustion and Emissions for Engineers

2019-12-09
Public awareness regarding pollutants and their adverse health effects has created an urgent need for engineers to better understand the combustion process as well as the pollutants formed as by-products of that process. To effectively contribute to emission control strategies and design and develop emission control systems and components, a good understanding of the physical and mathematical principles of the combustion process is necessary. This seminar will bring issues related to combustion and emissions "down to earth," relying less on mathematical terms and more on physical explanations and analogies.
Technical Paper

Valve Flow Coefficients under Engine Operation Conditions: Piston Influence and Flow Pulsation

2019-08-15
2019-24-0003
Engine valve flow coefficients are used to describe the flow throughput performance of engine valve/port designs, and to model gas exchange in 0D/1D engine simulation. Valve flow coefficients are normally estimated at a stationary flow test bench, separately for intake and exhaust side, in the absence of the piston. However, engine operation differs from this setup; i. a. the piston might interact with valve flow around scavenging top dead center, and instead of steady boundary conditions, valve flow is nearly always subjected to pressure pulsations, due to pressure wave reflections within the gas exchange ports. In this work the influences of piston position and pressure pulsation on valve flow coefficients are investigated for different SI engine geometries by means of 3D CFD and measurements at an enhanced flow test bench.
Technical Paper

Development of 1D/0D cycle simulation model for highly lean burn SI engine operation

2019-08-15
2019-24-0004
In the development processes for an engine control scheme and a novel engine configuration, 1D or 0D engine cycle simulation is effective and has been widely utilized, in these years. In SI engines, engine operations with the highly lean air-fuel mixture or highly diluted with EGR gas have been known as one of the most effective strategies to save fuel consumption. Following these situations, it is strongly demanded to develop a predictive combustion model capable of accurately predicting the effects of air-fuel ratio and EGR ratio on combustion characteristics, and thus on engine performance. In this paper, to predict highly lean or EGR diluted combustion with enough accuracy in 1D/0D engine simulation, a spark ignition model capable of predicting spark discharge circuit and a spark discharge channel behavior in the cylinder, and a flamelet concept model were applied into a single cylinder engine performance prediction model.
Technical Paper

CFD Investigation of the Effects of Gas’ Methane Number on the Performance of a Heavy-Duty Natural-Gas Spark-Ignition Engine

2019-08-15
2019-24-0008
Natural gas (NG) is an alternative fuel for spark-ignition engines. In addition to its cleaner combustion, recent breakthroughs in drilling technologies increased its availability and lowered its cost. NG consists of mostly methane, but it also contains heavier hydrocarbons and inert diluents, the levels of which vary substantially with geographical source, time of year, and treatments applied during production or transportation. To investigate the effects of NG composition on engine performance and emissions, a 3D CFD model of a heavy-duty diesel engine retrofitted to spark ignition operations simulated engine operation under lean-combustion, low-speed, and medium load conditions. To eliminate the effect of different gas energy density, three NG blends of similar lower heating value but different H/C ratio have been investigated at fixed spark timing.
Technical Paper

MULTI-LEVEL MODELING OF REAL SYNGAS COMBUSTION IN A SPARK IGNITION ENGINE AND EXPERIMENTAL VALIDATION

2019-08-15
2019-24-0012
Syngas produced from biomass gasification is being increasingly considered as a promising alternative to traditional fuels in Spark-Ignition (SI) Internal Combustion Engines (ICEs). This gaseous fuel, composed by a mixture of CO, CH4, H2, CO2, N2 (and other minor hydrocarbon compounds), is however characterized by an extreme variability of its composition and a low energy density. In order to assure good energy performance and stability of operation as the syngas composition slightly changes, numerical modeling can give an important contribution as a tool to investigate the main parameters affecting the combustion process development and the formation of main pollutants. The present work introduces a multi-level set of numerical approaches to a SI ICE fueled with syngas deriving from biomass gasification.
Technical Paper

Evaluation of water and EGR effects on combustion characteristics of GDI engines using a chemical kinetics approach

2019-08-15
2019-24-0019
The modern spark ignition engines, due to the introduced strategies for limiting the consumption without reducing the power, are sensitive to both the detonation and the increase of the inlet turbine temperature. In order to reduce the risk of detonation, the use of dilution with the products of combustion (EGR) is an established practice that has recently was improved with the use of water vapour obtained via direct or indirect injection. The application and optimization of these strategies cannot ignore the knowledge of physical quantities characterizing the combustion such as the laminar flame speed and the ignition delay, both are an intrinsic property of the fuel and are function of the mixture composition (mixture fraction and dilution) and of its thermodynamic conditions. The experimental measurements of the laminar flame speed and the ignition delay available in literature, rarely report the effects of dilution by EGR or water vapor.
Technical Paper

Impact of cooled EGR on performance and emissions of a turbocharged Spark-Ignition engine under low-full load conditions

2019-08-15
2019-24-0021
The stringent worldwide exhaust emission legislations for CO2 and pollutants require significant efforts to increase both the combustion efficiency and the emission quality of internal combustion engines. With this aim, several solutions are continuously produced to improve the combustion efficiency of spark ignition engines. Among the various solutions, EGR represents a well-established technology to improve the gasoline engine performance and the nitrogen-oxides emissions. This work presents the results of an experimental investigation on the effects of the EGR technique on combustion evolution, knock tendency, performance and emissions of a small–size turbocharged PFI SI engine, equipped with an external cooled EGR system. Measurements are carried out at different engine speeds, on a wide range of loads and EGR levels. The standard engine calibration is applied at the reference test conditions.
Technical Paper

A Review of Spark-Assisted Compression Ignition (SACI) Research in the Context of Realizing a Production SACI Strategy

2019-08-15
2019-24-0027
Low temperature combustion (LTC) strategies have been a keen interest in the automotive industry for over four decades since they offer improved fuel efficiency compared to conventional spark-ignition (SI) engines. LTC strategies use high dilution to keep combustion temperatures below about 2000 K to reduce heat transfer losses while avoiding locally rich in-cylinder regions that produce high soot. High dilution also enables an efficiency improvement from reduced pumping work and improved thermodynamic properties, though it requires high ignition energy. Combustion can be achieved by triggering autoignition from compression energy. High compression ratios are typically required to produce this level of ignition energy, which further improves fuel efficiency. The timing of the autoignition event is influenced by fuel properties and mixture composition, and is exponentially sensitive to temperature.
Technical Paper

Heavy-Duty Compression-Ignition Engines Retrofitted to Spark-Ignition Operation Fueled with Natural Gas

2019-08-15
2019-24-0030
Natural gas is a promising alternative gaseous fuel due to its availability, economic, and environmental benefits. A solution to increase its use in the heavy-duty transportation sector is to convert existing heavy-duty compression ignition engines to spark-ignition operation by replacing the fuel injector with a spark plug and injecting the natural gas inside the intake manifold. The use of numerical simulations to design and optimize the natural gas combustion in such retrofitted engines can benefit both engine efficiency and emission. However, experimental data of natural gas combustion inside a bowl-in-piston chamber is limited. Consequently, the goal of this study was to provide high-quality experimental data from such a converted engine fueled with methane and operated at steady-state conditions, exploring variations in spark timing, engine speed and equivalence ratio.
Technical Paper

Back-pressure and fuel type effects on exhaust gas oxygen sensor readings for a single cylinder spark ignition engine running on gasoline and ethanol

2019-08-15
2019-24-0046
Application of more and more complex control strategies in spark ignition (SI) engine is required for ensuring high conversion efficiency and effective emissions reduction. Closed loop fuel injection is being implemented on an ever wider scale in small size SI units that generally feature single cylinder architecture. For such systems the reading from the exhaust gas oxygen sensor is essential for controlling air-fuel ratio and indirectly combustion. The present study looked at the influence of pressure oscillations on the values given by the sensor, for different equivalence ratio settings in wide open throttle conditions for an experimental SI unit. As expected, the readings were found to be influenced by pressure oscillations in the exhaust line during lean operation, while with rich fueling the effects were minimal. Fuel type was also found to be an important aspect.
Technical Paper

Smart cylinder deactivation strategies to improve fuel economy and pollutant emissions for Diesel-powered applications

2019-08-15
2019-24-0055
Further improvement of the trade-off between CO2- and pollutant emissions is the main motivating factor for the development of new diesel engine concepts, from light-duty car applications via medium-duty commercial vehicles up to large long-haul trucks. The deactivation of one or more cylinders of a light-duty diesel engine during low load operation can be a sophisticated method to improve fuel economy and reduce especially NOx emissions at the same time. Dynamic Skip Fire (DSF) is and advanced cylinder deactivation technology, where the decision to fire or skip singular units of a multi-cylinder engine architecture is taken just prior to each firing opportunity, based on a balanced rankling of multiple input parameters.
Technical Paper

Quantification of Linear Approximation Error for Model Predictive Control of Spark Ignited Turbocharged Engines

2019-08-15
2019-24-0014
Modern turbocharged spark-ignition engines are being equipped with an increasing number of control actuators to simultaneously meet fuel economy, emissions and performance targets. The response time variations between a given set of engine control actuators tends to be significant during transients and necessitate highly complex actuator scheduling routines. Model Predictive Control (MPC) algorithms have the potential to significantly reduce calibration and control tuning efforts as compared to current methodologies that are designed around integration of multiple single-input single-output sub-system controllers. MPC systems simultaneously generate all actuator responses by using a combination of current engine conditions and optimization of a control-oriented plant model. To achieve real-time control the engine model and optimization processes must be computationally efficient without sacrificing effectiveness.
Technical Paper

Emissive behavior of a heavy-duty SI gas engine during WHTC

2019-08-15
2019-24-0121
In the arduous aim to reduce petroleum fuel consumption and toxic emissions, gaseous fuels can represent an alternative solution for heavy duty applications with respect to conventional liquid fuels. At the same time, the imposition of more stringent emissions regulations in the transport sector, is a crucial aspect to be considered also for the development of future gas engines. Scope of the present paper was to characterize a heavy duty spark ignition engine, under development for Euro VI compliance, with a particular focus on exhaust particulate emissions. In this sense, the engine was installed on a dynamic test bench, accurately instrumented to analyze combustion evolution, performance and exhaust pollutant emissions, along the World Harmonized Transient Cycle (WHTC).
Technical Paper

Experimental Investigation of Combustion Characteristics in a Heavy-Duty Compression-Ignition Engine Retrofitted to Natural-Gas Spark-Ignition Operation

2019-08-15
2019-24-0124
The conversion of existing diesel engines to natural gas operation can reduce U.S. dependence on petroleum imports and curtail engine-out emissions. Diesel compression ignition engines can be modified to NG spark ignition, by replacing the diesel injector with a NG spark plug and by fumigating NG in the intake manifold, to increase utilization of natural gas heavy-duty transportation sector. As the original diesel piston is maintained during conversion to decrease engine modification cost, the major of this study was to investigate the lean-burn characteristic of natural gas burning in this bowl-in-piston combustion chamber, which can accelerate the introduction of heavy-duty natural gas vehicles. Data analysis from engine experiments that changed spark timing indicated a two-stage combustion process in such retrofitted engines, which is different from traditional spark ignition engines.
Technical Paper

Development of Knock Prediction Model for a Spark-Ignition Engine with Gasoline-Ethanol-nButanol Blend Fuel by Using Rapid Compression Machine

2019-08-15
2019-24-0125
As an alternative fuel for spark-ignition (SI) engine, bio-derived alcohols have been used in several countries, which originate from various renewable resources. There have been numerous studies on the knocking characteristics of gasoline-ethanol blend fuel, however, less focus was on the ternary mixture of gasoline-ethanol-nbutanol (GEnB) blend fuel, which is being considered as an alternative fuel in South Korea and superior to gasoline-ethanol blend fuel due to its higher heating value for the same alcohol volume fraction. In this study, we developed a knocking prediction model in SI engine with GEnB blend fuel to understand the potential improvement of engine performance with the introduction of GEnB blend fuel. First, the ignition delay of the stoichiometric mixture of GEnB blend fuel and air was measured on 10–30 bar of pressure and 714–833 K of temperature by using rapid compression machine (RCM).
Technical Paper

Optical investigation of mixture formation in a small bore DISI engine by laser induced exciplex fluorescence (LIEF)

2019-08-15
2019-24-0133
Legislative and customer demands in terms of fuel consumption and emissions are an enormous challenge for the development of modern combustion engines. Downsizing in combination with turbocharging and direct injection is one way to increase efficiency and therefore meet the requirements. This results in a reduction of the displacement and thus the bore diameter. The application of direct injection with small cylinder dimensions increases the probability of the interaction of liquid fuel with the cylinder walls, which may result in disadvantages concerning especially particulate emissions. This leads to the question which bore diameter is feasible without drawbacks concerning emissions as a result of wall wetting. The emerging trends towards long-stroke engine design and hybridization make the use of small bore diameters in future gasoline engines a realistic scenario.
Technical Paper

Performance and Emissions of an Ammonia-Fueled SI Engine with Hydrogen Enrichment

2019-08-15
2019-24-0137
While the optimization of the internal combustion engine (ICE) remains a very important topic, alternative fuels are also expected to play a significant role in the reduction of CO2 emissions. High energy densities and handling ease are their main advantages amongst other energy carriers. Ammonia (NH3) additionally contains no carbon and has a worldwide existing transport and storage infrastructure. It could be produced directly from renewable electricity, water and air, and is thus currently considered as a smart energy carrier and combustion fuel. However, ammonia presents a low combustion intensity and the risk of elevated N-based emissions, thus rendering in-depth investigation of its suitability as an ICE fuel necessary. In the present study, a recent single-cylinder GDI SI engine is fueled with gaseous ammonia/hydrogen/air mixtures at various hydrogen fractions, equivalence ratios and intake pressures.
Technical Paper

Analysis of the effect of the sampling conditions on the sub-23nm particles emitted by a small displacement PFI and DI SI engines fuelled with gasoline and ethanol

2019-08-15
2019-24-0155
The growing concerns on the emission of particles smaller than 23 nm, which are harmful to human health, lead to the necessity of introducing a regulation for these particles not yet included in the current emission standards. Considering that measurements of concentration of sub-23nm particles are particularly sensitive to the sampling conditions, it is important to identify an effective assessment procedure. Aim of this paper is the characterization of the effect of the sampling conditions on sub-23nm particles, emitted by PFI and DI spark ignition engines fuelled with gasoline, ethanol and a mixture of ethanol and gasoline (E20). The experimental activity was carried out on a 250 cm3 displacement single cylinder engine, four stroke equipped with a prototype gasoline direct injection (GDI) head. The tests were conducted at 2000 rpm and 4000 rpm full load, representative of the homologation urban driving cycle.
Technical Paper

Impact of ethanol and aromatic hydrocarbons content on particulate emissions from a gasoline vehicle

2019-08-15
2019-24-0160
The impact of transport on global and local pollution have resulted in stricter emission limits. More specifically, increasing attention is being paid to particulate emissions at the exhaust gases in spark ignition engines. The particulate formation is mainly affected by: 1-fuel properties, 2-engine and fuel system characteristics and 3-Exhaust after-treatment system. In order to estimate the influence of fuel characteristics on particulate emissions, several research works have proposed fuel indices that correlate some of the fuel physical and chemical properties with engine particulate emissions. This work investigates the impact of fuel composition on particulate emissions and evaluates the Particulate Matter Index (PMI) proposed by Aikawa et. al, and other fuel indices, in terms of agreement with vehicle test bed results for a passenger car.
Technical Paper

Experimental Investigation of a Fuelled Prechamber combustion in an Optical Small Displacement SI Methane Engine

2019-08-15
2019-24-0170
The permanent aim of the automotive industry is the further improvement of engine efficiency and the simultaneous emissions reduction. In order to optimize the small internal combustion engines it is necessary to further improve the basic knowledge of the thermo-fluid dynamic phenomena occurring during the combustion process. In this context, the application of optical diagnostic techniques per-mits a deep insight into the fundamental processes such as flow development, fuel injection, and combustion process. In this paper the analysis of the combustion process of gaseous fuel ignited by the plasma jets coming from a prechamber were performed. The investigation was carried out in an optically accessible small Direct Injection Spark-Ignition (DI SI) engine fuelled with Methane. The ig-nition was obtained with a proper designed fuelled prechamber prototype equipped with a gas Direct Injector, used to inject the fuel into the prechamber, and a spark plug used to ignite the mixture.
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