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Technical Paper

A Comparative Analysis on the Spray Penetration of Ethanol, Gasoline and Iso-Octane Fuel in a Spark-Ignition Direct-Injection Engine

This study aims to clarify the spray development of ethanol, gasoline and iso-octane fuel, delivered by a multi-hole injector and spark-ignition direct-injection (SIDI) fuelling system. The focus is on how fuel properties impact temporal and spatial evolution of sprays at realistic ambient conditions. Two optical facilities were used: (1) a constant-flow spray chamber simulating cold-start conditions and (2) a single-cylinder SIDI engine running at normal, warmed-up operating conditions. In these optical facilities, high-speed Mie-scattering imaging is performed to measure penetrations of spray plumes at various injection pressures of 4, 7, 11 and 15 MPa. The results show that the effect of fuel type on the tip penetration length of the sprays depends on the injection conditions and the level of fuel jet atomisation and droplet breakup.
Journal Article

A Comparative Assessment of Electric Propulsion Systems in the 2030 US Light-Duty Vehicle Fleet

This paper quantifies the potential of electric propulsion systems to reduce petroleum use and greenhouse gas (GHG) emissions in the 2030 U.S. light-duty vehicle fleet. The propulsion systems under consideration include gasoline hybrid-electric vehicles (HEVs), plug-in hybrid vehicles (PHEVs), fuel-cell hybrid vehicles (FCVs), and battery-electric vehicles (BEVs). The performance and cost of key enabling technologies were extrapolated over a 25-30 year time horizon. These results were integrated with software simulations to model vehicle performance and tank-to-wheel energy consumption. Well-to-wheel energy and GHG emissions of future vehicle technologies were estimated by integrating the vehicle technology evaluation with assessments of different fuel pathways. The results show that, if vehicle size and performance remain constant at present-day levels, these electric propulsion systems can reduce or eliminate the transport sector's reliance on petroleum.
Technical Paper

A Comparative Study Between 1D and 3D Computational Results for Turbulent Flow in an Exhaust Manifold and in Bent Pipes

To improve today’s 1D engine simulation techniques it is important to investigate how well complex geometries such as the manifold are modeled by these engine simulation tools and to identify the inaccuracies that can be attributed to the 1D assumption. Time resolved 1D and 3D calculations have been performed on the turbulent flow through the outer runners of an exhaust manifold of a 2 liter turbocharged SI engine passenger car The total pressure drop over the exhaust manifold, computed with the 1D and 3D approach, showed to differ over an exhaust pulse. This is so even though a pressure loss coefficient correction has been employed in the 1D model to account for 3D flow effects. The 3D flow in the two outer runners of the manifold shows the presence of secondary flow motion downstream of the first major curvature. The axial velocity profile downstream of the first turn loses its symmetry. As the flow enters the second curvature a swirling motion is formed.
Journal Article

A Comparative Study of Directly Injected, Spark Ignition Engine Combustion and Energy Transfer with Natural Gas, Gasoline, and Charge Dilution

Abstract This article presents an investigation of energy transfer, flame propagation, and emissions formation mechanisms in a four-cylinder, downsized and boosted, spark ignition engine fuelled by either directly injected compressed natural gas (DI CNG) or gasoline (GDI). Three different charge preparation strategies are examined for both fuels: stoichiometric engine operation without external dilution, stoichiometric operation with external exhaust gas recirculation (EGR), and lean burn. In this work, experiments and engine modelling are first used to analyze the energy transfer throughout the engine system. This analysis shows that an early start of fuel injection (SOI) improves fuel efficiency through lower unburned fuel energy at low loads with stoichiometric DI CNG operation.
Technical Paper

A Comparative Study of Knock Formation in Gasoline and Methanol Combustion Using a Multiple Spark Ignition Approach: An Optical Investigation

Engine knock is a major challenge that limits the achievement of higher engine efficiency by increasing the compression ratio of the engine. To address this issue, using a higher octane number fuel can be a potential solution to reduce or eliminate the propensity for knock and so obtain better engine performance. Methanol, a promising alternative fuel, can be produced from conventional and non-conventional energy resources, which can help reduce pollutant emissions. Methanol has a higher octane number than typically gasolines, which makes it a viable option for reducing knock intensity. This study compared the combustion characteristics of gasoline and methanol fuels in an optical spark-ignition engine using multiple spark plugs. The experiment was carried out on a single-cylinder four-stroke optical engine. The researchers used a customized metal liner with four circumferential spark plugs to generate multiple flame kernels inside the combustion chamber.
Journal Article

A Comparative Study of a Spark Ignition Engine Running on Hydrogen, Synthesis Gas and Natural Gas

This paper presents an experimental, numerical and theoretical study of the performance of the same spark ignition engine running on four different gaseous fuels: hydrogen, two synthesis gases and natural gas. Measurements of the brake thermal efficiency, the combustion variability, the engine out emissions and the indicated, pumping and friction mean effective pressures are first presented, with particular interest placed on the lean burn performance. Combustion analysis is then undertaken, with the crank angle resolved in-cylinder turbulence and the flame propagation plotted on the so-called ‘Bradley diagram’ for turbulent premixed combustion. The loci of the combustion events on the Bradley diagram are then used to explain the observed, relative performance of the engine running on these four fuels.
Journal Article

A Comparison Between External and Internal Resonators Employment to Reduce the Gas-Dynamic Noise of a SI Engine

This paper reports 1D and 3D CFD analyses aiming to improve the gas-dynamic noise emission of a downsized turbocharged VVA engine through the re-design of the intake air-box device, consisting in the introduction of external or internal resonators. Nowadays, modern spark-ignition (SI) engines show more and more complex architectures that, while improving the brake specific fuel consumption (BSFC), may be responsible for the increased noise radiation at the engine intake mouth. In particular VVA systems allow for the actuation of advanced valve strategies that provide a reduction in the BSFC at part load operations thanks to the intake line de-throttling. In these conditions, due to a less effective attenuation of the pressure waves that travel along the intake system, VVA engines produce higher gas-dynamic noise levels.
Technical Paper

A Comparison Between Two Phenomenological Combustion Models Applied to Different SI Engines

Nowadays, the development of a new engine is becoming more and more complex due to conflicting factors regarding technical, environmental and economic issues. The experimental activity has to comply with the above complexities, resulting in increasing cost and duration of engine development. For this reason, the simulation is becoming even more prominent, thanks to its lower financial burden, together with the need of an improved predictive capability. Among the other numerical approaches, the 1D models represent a proper compromise between reliability and computational effort, especially if the engine behavior has to be investigated over a number of operating conditions. The combustion model has a key role in this contest and the research of consistent approaches is still on going. In this paper, two well-assessed combustion models for Spark Ignition (SI) engines are described and compared: the eddy burn-up theory and the fractal approach.
Technical Paper

A Comparison Study on Saving Fuel by Idle-Stop System in Bangkok Traffic Condition

This paper presents an investigation on fuel consumption in Bangkok traffic condition with an application of idle stop system. Collected data is evaluated by cutoff the fuel usage while the vehicle is in stationary condition. The vehicles in this study are ordinary vehicle which is not the vehicle with idle-stop system. The study includes four levels of congestion and three road side conditions. With idle stop system, for spark ignition engine 40% of fuel consumption rate could be improved in severe condition and 10% improvement in free flow traffic. In addition, the fuel consumption can be improved by 30% for compression ignition engine. Furthermore, the idle stop system improves fuel efficiency in severe congestion to the same level as the free flow traffic
Technical Paper

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

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

A Comparison of Burn Characteristics and Exhaust Emissions from Off-Highway Engines Fueled by E0 and E85

Ethanol fuel has received renewed attention in recent years because of its oxygenate content and its potential to reduce greenhouse gas emissions from spark ignition engines. The economic impact on farm industry has been one of the drivers for its use in engines in the U.S. Although ethanol, in various blends, has been used in automotive engines for almost a decade the fuel has seldom been utilized in off-highway engines where the fuel systems are not well controlled. This investigation was conducted to evaluate exhaust emissions and combustion characteristics of E85 fuel in an off-highway engine used in farm equipment. A single-cylinder, four-stroke, spark ignition engine equipped with a carburetor was used to investigate combustion and exhaust emissions produced by gasoline and blends of gasoline and ethanol fuels. The engine fuel system was modified to handle flow rates required by the engine. A variable size-metering orifice was used to control air-to-fuel ratios.
Technical Paper

A Comparison of Combustion Temperature Models for Ionization Current Modeling in an SI Engine

Combustion temperature models for spark ignited engines are investigated in this work. The temperature models are evaluated as sub-models of a model for the thermal part of ionization current. Three different combustion temperature models were investigated; a single-zone model, a mixed two-zone model and an unmixed two-zone called a kernel-zone model. The combustion temperature is derived from cylinder pressure. The ionization current model structure also contain sub-models for formation of nitric oxide (NO) and its thermal ionization. The model output is compared to the measured ionization currents with respect to peak amplitude and position. Also, two models for NO formation are evaluated. The first is a fixed NO molar fraction model and the second is a reaction rate controlled NO formation model based on the extended Zeldovich reaction scheme.
Technical Paper

A Comparison of EGR Condensate Composition between EGR and Dedicated-EGR Combustion Strategies

Water injection is an effective method for knock control in spark-ignition engines. However, the requirement of a separate water source and the cost and complexity associated with a fully integrated system creates a limitation of this method to be used in volume production engines. The engine exhaust typically contains 10-15% water vapor by volume which could be condensed and potentially stored for future use. In this study, the exhaust condensate composition was assessed for its use as an effective replacement for distilled water. Specifically, condensate samples were collected pre and post-three-way catalyst (TWC) and analyzed for acidity and composition. The composition of the pre and post-TWC condensates was found to be similar however, the pre-TWC condensate was mildly acidic. The mild acidity has the potential to corrode certain components in the intake air circuit.
Journal Article

A Comparison of EGR Correction Factor Models Based on SI Engine Data

Abstract The article compares the accuracy of different exhaust gas recirculation (EGR) correction factor models under engine conditions. The effect of EGR on the laminar burning velocity of a EURO VI E10 specification gasoline (10% Ethanol content by volume) has been back calculated from engine pressure trace data, using the Leeds University Spark Ignition Engine Data Analysis (LUSIEDA) reverse thermodynamic code. The engine pressure data ranges from 5% to 25% EGR (by mass) with the running conditions, such as spark advance and pressure at intake valve closure, changed to maintain a constant engine load of 0.79 MPa gross mean effective pressure (GMEP). Based on the experimental data, a correlation is suggested on how the laminar burning velocity reduces with increasing EGR mass fraction.
Technical Paper

A Comparison of Four Methods for Determining the Octane Index and K on a Modern Engine with Upstream, Port or Direct Injection

Combustion in modern spark-ignition (SI) engines is increasingly knock-limited with the wide adoption of downsizing and turbocharging technologies. Fuel autoignition conditions are different in these engines compared to the standard Research Octane Number (RON) and Motor Octane Numbers (MON) tests. The Octane Index, OI = RON - K(RON-MON), has been proposed as a means to characterize the actual fuel anti-knock performance in modern engines. The K-factor, by definition equal to 0 and 1 for the RON and MON tests respectively, is intended to characterize the deviation of modern engine operation from these standard octane tests. Accurate knowledge of K is of central importance to the OI model; however, a single method for determining K has not been well accepted in the literature.
Technical Paper

A Comparison of Fuel Distribution and Combustion During Engine Cold Start for Direct and Port Fuel Injection Systems

Experiments have been conducted in a firing single-cylinder spark-ignition engine employing a Ford Zetec cylinder head that has been modified to operate with either standard port-fuel-injection, air-forced port-fuel-injection or direct-injection. The engine utilizes a fused silica cylinder and therefore provides extensive optical access to the combustion chamber. Tests were conducted using a constant speed simulated cold start procedure, which is composed of an initial start-up transient and a quasi-steady-state idle period. In this procedure, the engine is briefly motored at 889 rpm and then combustion commences shortly after the start of fuel injection. Measurements which were performed include in-cylinder pressure as well as intake valve, exhaust valve, piston, cylinder, head, and intake air temperature throughout each cycle of the test period. The engine-out total hydrocarbon emissions were also measured.
Technical Paper

A Comparison of Hydrocarbon Emissions from Different Piston Designs in an SI Engine

The total hydrocarbon emissions and the distribution of hydrocarbon species from the emissions of two different piston and cylinder liner designs; 1 reduced top land height, 2 smoother cylinder bore, were compared with a standard production Rover K16 spark ignited engine. Reductions in total HC emissions were achieved for both designs. The variations between the relative quantities of a selection of the most significant species were investigated for each design, considerable differences were observed between these design changes.
Technical Paper

A Comparison of Ion Current Based Algorithms for Peak Pressure Position Control

Combustion timing control of SI engines can be improved by feedback of the peak pressure position (PPP). However, pressure sensors are costly, and therefore, nonintrusive and cheap ion-current ‘soft sensors’ have been suggested. Three different algorithms have been proposed that extract information about PPP from the ion current signal. In this paper, these approaches are compared with respect to accuracy, operational range, implementation aspects, as well as sensitivity to engine load and inlet air humidity.
Technical Paper

A Comparison of Methanol, Methane and Hydrogen Fuels for SI Engines: Performance and Pollutant Emissions

The urban mobility electrification has been proposed as the main solution to the vehicle emission issues in the next years. However, internal combustion engines have still great potential to decarbonize the transport sector through the use of low/zero-carbon fuels. Alcohols such us methanol, have long been considered attractive alternative fuels for spark ignition engines. They have properties similar to those of gasoline, are easy to transport and store. Recently, great attention has been devoted to gaseous fuels that can be used in existing engine after minor modification allowing to drastically reduce the pollutant emissions. In this regard, this study tries to provide an overview on the use of alternative fuels, both liquid and gaseous in spark ignition engines, highlighting the benefits as well as the criticalities. The investigation was carried out on a small displacement spark ignition engine capable to operate both in port fuel and direct injection mode.
Journal Article

A Comparison of Spray-Guided Stratified-Charge Combustion Performance with Outwardly-Opening Piezo and Multi-Hole Solenoid Injectors

This investigation was aimed at measuring the relative performance of two spray-guided, single-cylinder, spark-ignited direct-injected (SIDI) engine combustion system designs. The first utilizes an outwardly-opening poppet, piezo-actuated injector, and the second a conventional, solenoid operated, inwardly-opening multi-hole injector. The single-cylinder engine tests were limited to steady state, warmed-up conditions. The comparison showed that these two spray-guided combustion systems with two very different sprays had surprisingly close results and only differed in some details. Combustion stability and smoke emissions of the systems are comparable to each other over most of the load range. Over a simulated Federal Test Procedure (FTP) cycle, the multi-hole system had 15% lower hydrocarbon and 18% lower carbon monoxide emissions.