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Journal Article

1D Numerical and Experimental Investigations of an Ultralean Pre-Chamber Engine

Abstract In recent years, lean-burn gasoline Spark-Ignition (SI) engines have been a major subject of investigations. With this solution, in fact, it is possible to simultaneously reduce NOx raw emissions and fuel consumption due to decreased heat losses, higher thermodynamic efficiency, and enhanced knock resistance. However, the real applicability of this technique is strongly limited by the increase in cyclic variation and the occurrence of misfire, which are typical for the combustion of homogeneous lean air/fuel mixtures. The employment of a Pre-Chamber (PC), in which the combustion begins before proceeding in the main combustion chamber, has already shown the capability of significantly extending the lean-burn limit. In this work, the potential of an ultralean PC SI engine for a decisive improvement of the thermal efficiency is presented by means of numerical and experimental analyses.
Technical Paper

1D and 3D CFD Investigation of Burning Process and Knock Occurrence in a Gasoline or CNG fuelled Two-Stroke SI Engine

The paper presents a combined experimental and numerical investigation of a small unit displacement two-stroke SI engine operated with gasoline and Natural Gas (CNG). A detailed multi-cycle 3D-CFD analysis of the scavenging process is at first performed in order to accurately characterize the engine behavior in terms of scavenging patterns and efficiency. Detailed CFD analyses are used to accurately model the complex set of physical and chemical processes and to properly estimate the fluid-dynamic behavior of the engine, where boundary conditions are provided by a in-house developed 1D model of the whole engine. It is in fact widely recognized that for two-stroke crankcase scavenged, carbureted engines the scavenging patterns (fuel short-circuiting, residual gas distribution, pointwise lambda field, etc.) plays a fundamental role on both of engine performance and tailpipe emissions.
Journal Article

4 L Light Duty LPG Engine Evaluated for Heavy Duty Application

Many applications of liquefied petroleum gas (LPG) to commercial vehicles have used their corresponding diesel engine counterparts for their basic architecture. Here a review is made of the application to commercial vehicle operation of a robust 4 L, light-duty, 6-cylinder in-line engine produced by Ford Australia on a unique long-term production line. Since 2000 it has had a dedicated LPG pick-up truck and cab-chassis variant. A sequence of research programs has focused on optimizing this engine for low carbon dioxide (CO₂) emissions. Best results (from steady state engine maps) suggest reductions in CO₂ emissions of over 30% are possible in New European Drive Cycle (NEDC) light-duty tests compared with the base gasoline engine counterpart. This has been achieved through increasing compression ratio to 12, running lean burn (to λ = 1.6) and careful study (through CFD and bench tests) of the injected LPG-air mixing system.
Technical Paper

A 3D-Simulation with Detailed Chemical Kinetics of Combustion and Quenching in an HCCI Engine

A 3D-CFD model with detailed chemical kinetics was developed to investigate the combustion characteristics of HCCI engines, especially those fueled with hydrogen and n-heptane. The effects of changes in some of the key important variables that included compression ratio and chamber surface temperature on the combustion processes were investigated. Particular attention was given, while using a finer 3-D mesh, to the development of combustion within the chamber crevices between the piston top-land and cylinder wall. It is shown that changes in the combustion chamber wall surface temperature values influence greatly the autoignition timing and location of its first occurrence within the chamber. With high chamber wall temperatures, autoignition takes place first at regions near the cylinder wall while with low surface temperatures; autoignition takes place closer to the central region of the mixture charge.
Technical Paper

A CNG Specific Fuel Injector Using Latching Solenoid Technology

An advanced fuel injector designed specifically for low energy density gaseous fuels has been developed which demonstrates compelling performance advantages over fuel injectors utilizing conventional solenoid technology. The injector incorporates design features that are necessary to optimize the performance for fuels such as CNG, LNG, and propane. This paper provides a background of magnetic latching technology and addresses the application of the technology to an advanced, pressure balanced, gaseous fuel injector. Performance of the injector will be discussed in detail as will features of the injector specifically adapted for gaseous applications. The ability of the injector to solve fuel metering problems facing the industry, such as turn down ratio limitations, accuracy, durability, and compatibility with existing engine electronics, are addressed.
Journal Article

A Carbon Intensity Analysis of Hydrogen Fuel Cell Pathways

A hydrogen economy is an increasingly popular solution to lower global carbon dioxide emissions. Previous research has been focused on the economic conditions necessary for hydrogen to be cost competitive, which tends to neglect the effectiveness of greenhouse gas mitigation for the very solutions proposed. The holistic carbon footprint assessment of hydrogen production, distribution, and utilization methods, otherwise known as “well-to-wheels” carbon intensity, is critical to ensure the new hydrogen strategies proposed are effective in reducing global carbon emissions. When looking at these total carbon intensities, however, there is no single clear consensus regarding the pathway forward. When comparing the two fundamental technologies of steam methane reforming and electrolysis, there are different scenarios where either technology has a “greener” outcome.
Technical Paper

A Combustion Model with Reduced Kinetic Schemes for S.I. Engines Fuelled with Compressed Natural Gas

The paper describes the development of a reduced kinetic scheme for the evaluation of the main chemical species (particularly NO and CO) in premixed turbulent flame and its application to a quasi-dimensional combustion model for spark ignition engines. The proposed mechanism is based on the kinetic solution of three transport equations for NO, CO and H, coupled with the partial equilibrium of the so-called water-shuffle equations to derive the OH, O and H2 concentrations. The remaining species are computed applying the element conservation, while the required prompt levels were determined by a separate chemical 1D code for laminar combustion. The proposed chemical scheme was locally validated, considering a turbulent flame inside a premixed flow of air and methane, ignited by a parallel flow of hot gases, by means of a CFD simulation. Successively, it was embedded into a quasi-D thermodynamic combustion model developed by the authors for the simulation of S.I. and C.I. engines.
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 Performance and Emission Characteristics of CNG and Gasoline on a Single Cylinder S. I. Engine

In this study some experiments were carried out to evaluate fuel consumption and exhaust emissions of carbon monoxide (CO), oxides of nitrogen (NOx)) and hydrocarbons (HC) with compressed natural gas (CNG) and gasoline in a single cylinder engine. Compressed natural gas showed 3 to 5 percent higher thermal efficiency and 15 percent lower specific fuel consumption as compared to gasoline. Also CO emissions were lower by 30-80 percent in rich zone and NOx by about 12 percent at an equivalence of 1.0. At wide open throttle CNG operation resulted in 10 to 12 percent lower power output. However, thermal efficiency and brake specific fuel consumption (bsfc) was better with CNG as compared to gasoline. Dual spark plug operation increased power output by 3 to 5 percent.
Technical Paper

A Comparison Between the Combustion of Isooctane, Methanol, and Methane in Pulse Flame Combustors with Closed Loop A/F Control

CO/H2 (ratios i.e. water gas shift equilibria) in exhaust gases produced from the combustion of pure isooctane, methanol, and methane in a pulse flame combustor were measured. Measured CO/H2 ratios were directionally consistent with C/H ratios of the respective fuels. The average CO/H2 ratios in combusted isooctane, methanol, and methane were found to be 3.8, 1.25, and 2.0, respectively. The effect of these differences on feedback A/F control with a HEGO (heated exhaust gas oxygen) sensor were also examined. Feedback control of isooctane combustion produced operation very near to stoichiometry. On the other hand, the combustion of methanol under feedback control resulted in steady state lean operation while feedback control of methane combustion produced rich operation. For all three fuels, operation shifted in the lean direction as combustion efficiency was degraded.
Journal Article

A Comparison of Ammonia Emission Factors from Light-Duty Vehicles Operating on Gasoline, Liquefied Petroleum Gas (LPG) and Compressed Natural Gas (CNG)

Vehicular ammonia emissions are currently unregulated, even though ammonia is harmful for a variety of reasons, and the gas is classed as toxic. Ammonia emissions represent a serious threat to air quality, particularly in urban settings; an ammonia emissions limit may be introduced in future legislation. Production of ammonia within the cylinder has long been known to be very limited. However, having reached its light-off temperature, a three-way catalyst can produce substantial quantities of ammonia through various reaction pathways. Production of ammonia is symptomatic of overly reducing conditions within the three-way catalyst (TWC), and depends somewhat upon the particular precious metals used. Emission is markedly higher during periods where demand for engine power is higher, when the engine will be operating under open-loop conditions.
Technical Paper

A Comparison of the Emissions from Gasoline vs. Compressed Natural Gas for an Electronic Fuel Injected Two Cylinder, Four-Stroke Engine

Natural gas is a viable alternative to gasoline and diesel fuel because it is a clean burning fuel that is available from a large domestic reserve through a mature infrastructure. The heavy dependence of the small engine sector on oil, much of which is imported from foreign countries and the small engine sector's negative impact on the air quality in urban areas are two pervasive problems that can be helped by using Compressed Natural Gas (CNG) as a small engine fuel. In addition, CNG is typically over 80% methane, which is produced by the decay of organic material, so while natural gas is not renewable its use enables much of the infrastructure required for a methane-based renewable energy system. In order to determine the emissions benefit of using CNG as compared to gasoline in a small engine, a 750 cc 90 degree V Twin port-fuel-injected production engine rated at 29 horsepower (HP), designed and built by Kohler Inc.
Technical Paper

A Comprehensive Chemical Kinetic Investigation of the Combustion Processes of Lean Mixtures of Methane and Air

The combustion processes of of lean mixtures of methane in air is examined by employing a detailed chemical kinetic scheme consisting of 178 elementary reaction steps with 41 species. The changes with time in the concentrations of the major relevant reactive species are determined from the preignition reactions to the time near equilibrium conditions. The results of such an approach to the combustion process are considered over a wide range of initial temperatures (1000 K - 1600 K) and equivalence ratios (0.2 - 1.2) while the pressure was kept at atmospheric. Calculated results obtained while using this model tend to be in good agreement with the corresponding experimental values of ignition delay. The ignition delay of methane-air mixture correlated by the following empirical expression in which constants A and B are function of the equivalence ratio while Ti is the initial mixture temperature in °K.
Technical Paper

A Compressed Natural Gas Mass Flow Driven Heavy Duty Electronic Engine Management System

This paper describes the conversion of a stationary spark ignition engine to a heavy duty (HD) natural gas engine suitable for transportation applications, in response to the new urban truck and bus legislation of 1994 and 1998. The approach to the fuel and ignition control system is to use a microprocessor controlled engine management system based on inputs from combustion air and natural gas mass flow sensors. As the emission control system is also based on stoichiometric three way catalyst technology, it is felt that the control approach is very robust. The engine and control system were first mounted on a HD dynamometer for the development work where engine control parameters were calibrated. In addition steady state emission data were collected and estimates of the HD transient emission levels were obtained.
Technical Paper

A Computational Investigation of the Effect of Exhaust Gas Recirculation on the Performance of a Dual Fuel Engine

It is well known the dual fuel operation at lower loads suffers from lower thermal efficiency and higher unburned percentages of fuel. The present work includes a computational investigation to predict the effects of Exhaust gas recirculation (EGR) on the operation of an indirect-injection dual fuel (Ricardo-E6) engine by using a detailed chemical kinetic scheme and a quasi-two zone analytical model. The comprehensive chemical kinetic scheme for methane oxidation consisting of 178 elementary reaction steps with 41 species. A quasi-two zone analytical model is based on the effective energy releases of the pilot diesel fuel while using the detailed chemical reaction kinetic scheme for the oxidation of methane. Through the results, it was shown that, the active species such as H, O and OH produced in the high temperature combustion process and found in the exhaust gases are play a significant role in the preignition reactions.
Technical Paper

A Controller for a Spark Ignition Engine with Bi-Fuel Capability

A bi-fuel engine with the ability to run optimally on both compressed natural gas (CNG) and gasoline is being developed. Such bi-fuel automotive engines are necessary to bridge the gap between gasoline and natural gas as an alternative fuel while natural gas fueling stations are not yet common enough to make a dedicated natural gas vehicle practical. As an example of modern progressive engine design, a Saturn 1.9 liter 4-cylinder dual overhead cam (DOHC) engine has been selected as a base powerplant for this development. Many previous natural gas conversions have made compromises in engine control strategies, including mapped open-loop methods, or resorting to translating the signals to or from the original controller. The engine control system described here, however, employs adaptive closed-loop control, optimizing fuel delivery and spark timing for both fuels.
Technical Paper

A Current Look at the Natural Gas Fueling Infrastructure in the United States

The natural gas utility industry has led the development of the natural gas fueling infrastructure in the United States. Focusing primarily on compressed natural gas (CNG), the utility industry has built fueling stations to serve their own fleets and those of targeted customers. In addition, gas utility companies have formed partnerships with traditional fuel retailers to offer natural gas to a broader range of customers. This paper will: Document the history of natural gas fueling infrastructure development from the early 1980's. It will provide statistics on the current status of the fueling infrastructure, including the numbers of private and public access stations and will forecast the number of stations required to serve projected natural gas vehicles (NGVs) through the year 2010. Examine the various types of CNG fueling technologies currently being used, and will discuss the major components of fueling systems.