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Technical Paper

Environmental, Thermodynamic and Chemical Factor Effects on Heptane- and CNG-fuelled HCCI Combustion with Various Mixture Compositions

2008-04-14
2008-01-0038
At certain operating conditions, Homogeneous Charge Compression Ignition (HCCI) can provide ultra-low NOx emissions with good combustion efficiency. However, using HCCI operating modes in a SI-based engine still requires some means to control HCCI ignition over a range of operating conditions. Amongst various possible control techniques, altering fuel ignition quality by blending a reformer gas mixture with base fuel is attractive, primarily because of the capability to alter fuel injection ratios on a cycle-by-cycle basis. As well as fuel blending, the mixture composition is defined by equivalence ratio (ϕ) and exhaust gas recirculation (EGR) ratio. The effects of changing such parameters have been widely studied both experimentally and with models. However, adjusting any variable has multiple effects on the mixture's thermodynamic and chemical properties so a detailed understanding of how these variables affect combustion is generally difficult to achieve.
Technical Paper

Study of Reformer Gas Effects on n-Heptane HCCI Combustion Using a Chemical Kinetic Mechanism Optimized by Genetic Algorithm

2008-04-14
2008-01-0039
Because of the potential for low NOx emissions with high efficiency, HCCI engines could develop a significant niche in the engine world. However, HCCI engines suffer from a narrow operating range between knock and misfire boundaries because the ignition timing is only controlled by mixture chemistry and compression conditions. Varying combinations of operating parameters are required to obtain good combustion under different conditions and chemical kinetic models are widely used as an engine research tool. The performance of such models depends critically on the accuracy of the chemical mechanisms which are still under development and require some optimization, particularly for larger hydrocarbon molecules. This study starts with a Chalmers University mechanism [1] which is well-proven for pure n-heptane but works less well for mixtures blended with significant amounts of reformer gas containing high fractions of H2 and CO [2].
Technical Paper

Reformer Gas Composition Effect on HCCI Combustion of n-Heptane, iso-Octane, and Natural Gas

2008-04-14
2008-01-0049
Although HCCI engines promise low NOx emissions with high efficiency, they suffer from a narrow operating range between knock and misfire because they lack a direct means of controlling combustion timing. A series of previous studies showed that reformer gas, (RG, defined as a mixture of light gases dominated by hydrogen and carbon monoxide), can be used to control combustion timing without changing mixture dilution, (λ or EGR) which control engine load. The effect of RG blending on combustion timing was found to be mainly related to the difference in auto-ignition characteristics between the RG and base fuel. The practical effectiveness of RG depends on local production using a fuel processor that consumes the same base fuel as the engine and efficiently produces high-hydrogen RG as a blending additive.
Technical Paper

Effect of Reformer Gas on HCCI Combustion - Part I:High Octane Fuels

2007-04-16
2007-01-0208
Homogeneous Charge Compression Ignition (HCCI) engines offer high fuel efficiency and some emissions benefits. However, it is difficult to control and stabilize combustion over a sufficient operating range because the critical compression ratio and intake temperature at which HCCI combustion can be achieved varies with operating conditions such as speed and load as well as with fuel octane number. Replacing part of the base fuel with reformer gas, (which can be produced from the base hydrocarbon fuel), alters HCCI combustion characteristics in varying ways depending on the replacement fraction and the base fuel auto-ignition characteristics. Injecting a blend of reformer gas and base fuel offers a potential HCCI combustion control mechanism because fuel injection quantities and ratios can be altered on a cycle-by-cycle basis.
Technical Paper

Effect of Reformer Gas on HCCI Combustion - Part II: Low Octane Fuels

2007-04-16
2007-01-0206
Homogeneous Charge Compression Ignition (HCCI) combustion offers high fuel efficiency and some emissions benefits. However, it is difficult to control and stabilize combustion over a significant operating range because the critical compression ratio and intake temperature at which HCCI combustion can be achieved vary with operating conditions such as speed and load as well as with fuel octane number. Replacing part of the base fuel with reformer gas, (which can be produced from the base hydrocarbon fuel), alters HCCI combustion characteristics in varying ways depending on the replacement fraction and the base fuel auto-ignition characteristics. Because fuel injection quantities and ratios can be altered on a cycle-by-cycle basis during operation, injecting a variable blend of reformer gas and base fuel offers a potential HCCI combustion control mechanism.
Technical Paper

Novel Method of Setting Initial Conditions for Multi-Zone HCCI Combustion Modeling

2007-04-16
2007-01-0674
Combustion in Homogeneous Charge Compression Ignition (HCCI) engines is the subject of intensive combustion modeling efforts because, while they have potential for low fuel consumption and emissions, they also suffer from problems of combustion control. Modeling studies are being used to predict the effects of changing controllable parameters and to ‘measure’ important combustion-related phenomena which can not be observed directly. A significant limitation of most current combustion models is that they still rely on arbitrarily adjusting initial conditions, (especially temperature) in order to match experimental results. This limits the confidence with which models can be used to predict HCCI combustion behavior over any range of conditions wider than available experimental data. This paper describes a new method to solve the initial condition problems for HCCI combustion modeling based on simulated heat transfer between intake and residual components.
Technical Paper

Emission Factors Analysis for Multiple Vehicles Using an On-Board, In-Use Emissions Measurement System

2007-04-16
2007-01-1327
Despite progressive implementation of stringent emission regulations, vehicle tailpipe emissions remain the major source of air pollution problems in most urban areas. To control and reduce tailpipe pollutants, it is critical to understand in-use emissions as a basis for any future emission controls. At present, emission factors are mainly studied by chassis dynamometer methods. However, concerns have been raised about the extent to which emissions produced by on-road vehicles can be predicted using emission factors developed based on standardized dynamometer test procedures. This paper describes an on-board, in-use vehicle emissions measurement system which measures tailpipe emission rates while the vehicle is in real service experiencing complex traffic conditions, driver behavior and weather.
Technical Paper

Experimental Measurement of On-Road CO2 Emission and Fuel Consumption Functions

2007-04-16
2007-01-1610
Motorized transport has become an essential part of our world economic system with an ever-increasing number of vehicles on the road. However, considering the depletion of energy resources and the aggravation of greenhouse gas issues, it is critical to improve vehicle fuel consumption. These demands are moving us toward advanced engine and powertrain technologies. However, understanding our progress also requires improvements in the way we measure and certify vehicle emissions and fuel economy performance. This paper describes the use of an on-board fuel consumption and emissions measurement system to develop on-road fuel consumption functions that can be used to quantify the fuel economy impact of vehicle, road and traffic control changes. The system uses an ECM OBD-II scanner, a Mass Air Flow meter and an emissions analyzer to monitor fuel consumption and exhaust CO2 emission rates (in g/s) as well as vehicle speed and other parameters.
Technical Paper

Using Reformer Gas to Enhance HCCI Combustion of CNG in a CFR Engine

2006-10-16
2006-01-3247
This paper describes use of reformer gas (RG) to alter and control combustion in a CNG-fueled HCCI engine. Experimental work used a mixture of simulated RG (75% H2 and 25% CO) to supplement base CNG fueling in a CFR engine upgraded to achieve high compression ratios. RG was used to improve the engine's operating performance and to control combustion onset in experiments conducted at three different compression ratios. A combination of high compression ratio (18.5) and high intake temperature (140°C) was observed to be appropriate to run the CNG-fueled CFR engine in HCCI mode. RG replacement of CNG altered combustion characteristics and expanded the operating range on the lean side. Use of RG decreased knock severity and reduced NOx emission. At constant relative air/fuel ratio (λ) it advanced combustion timing, moving the maximum cylinder pressure earlier in the cycle and increasing maximum pressure.
Technical Paper

The Effects of Temperature and Pressure on Stretched, Freely Propagating, Premixed, Laminar Methane-Air Flame

2006-04-03
2006-01-0494
Flame stretch arises due to strain and change in flame curvature and is extremely important in spark ignition (SI) engine combustion. It can significantly alter the flame speed and hence, the burning duration. This, in turn, can have serious influence on engine performance and exhaust emission. A good understanding of stretch effect can thus lead to improved fuel efficiency, reduced cyclic variations, and better emission control for SI engines. In this study, we analyzed initial temperature and pressure effects on the stretched flame speed of a laminar, premixed, freely propagating, spherical methane-air flame in accordance with the Markstein theory, which postulates a linear relationship between stretched and unstretched flame speed. The unstretched flame speed was computed using CHEMKIN GUI 4.0.1 with GRI Mech 3.0 reaction mechanism. Analytical expressions relating stretched and unstretched flame speed were employed to derive the stretched flame speed.
Technical Paper

A Fuel Quality Sensor for Fuel Cell Vehicles, Natural Gas Vehicles, and Variable Gaseous Fuel Vehicles

2005-10-24
2005-01-3770
There are many possible applications for the discrete acoustic wave and phase detection (DAWPD) sound speed sensor. The DAWPD sensor is a compact sensor that measures the sound speed of gases. The sound speed of gaseous fuels can be related to various properties of a fuel including composition. A sound speed sensor can be used as a fuel quality sensor in natural gas vehicles (NGVs), variable gaseous fuel (VGF) vehicles (a VGF vehicle uses a mixture of hydrogen and natural gas fuel), and proton exchange membrane (PEM) fuel cell vehicles (FCVs). In a NGV the DAWPD sensor can be used to measure the methane number, Wobbe number, and hydrogen-to-carbon ratio of the natural gas. The DAWPD sensor can also be used to find the composition of the fuel used in VGF vehicles. In PEM fuel cell vehicles small amounts of CO (>25 ppm) can poison the fuel cell. The DAWPD sensor can measure the amount of CO in the hydrogen fuel in order to control the fuel reforming process.
Technical Paper

Time Resolution Effects on Accuracy of Real-Time NOx Emissions Measurements

2005-04-11
2005-01-0674
The advanced development of a previous in-use emissions measurement system developed at the University of Alberta, has been used to illustrate the challenges in accurately measuring real-time mass emissions of NOx, with specific attention given to the issue of sensor time resolution. An analysis of the alignment of vehicle and emissions data has shown constant value time shifting of remote emissions sensor data, to match vehicle data, as the most accurate method for synchronization. Although variable time shifting routines theoretically determine alignment time more accurately, the variable shifting of slow response sensor data has shown an added smearing effect to time shifted remote analyzer data. The effect of sensor response time on accuracy of mass emission rates, has shown that slow response remote emissions sensors are under predicting the total emissions produced by vehicles.
Technical Paper

A Numerical Study on the Burning Velocity of a Spherical, Premixed Methane-Air Flame

2005-04-11
2005-01-1124
As a first step toward better understanding of the effects of flame stretch on combustion rate in SI engines, the burning velocity of a premixed, spherical, laminar methane-air flame propagating freely at standard temperature and pressure was investigated. The underlying un-stretched burning velocity was computed using CHEMKIN 3.7 with GRI mechanism, while the Lewis number and subsequently the Markstein length were deduced theoretically. The burning velocity of the freely growing flame ball was calculated from the un-stretched burning velocity with curvature and stretch effects accounted via the theoretically deduced Markstein length. For the positive Markstein length methane-air flame, flame stretching reduces the burning velocity. Therefore, the burning velocity of a spark-ignited flame starts with a value lower than, and increases asymptotically to, the underlying un-stretched burning velocity as the flame grows.
Technical Paper

Life Cycle Analysis of Biomass Transportation: Trains vs. Trucks

2005-04-11
2005-01-1551
Biomass is regarded as a renewable resource for upgrading to solid or liquid fuels or for electricity generation. Because its energy density is very low compared to petroleum or coal, the cost of transporting biomass is a significant part of the total biomass cost. For this reason it is usually regarded as a local resource. However, appropriate logistic systems may allow collection of biomass over a large geographical area, thus making it possible to consider efficient, large scale energy conversion systems. For areas without significant water transportation, the basic choices are between truck-based, train-based and pipeline transportation. Previous work has shown that pipeline transport is not effective for biomass delivery due to uptake of carrier fluid (water or oil) by the biomass. Hence, the choice becomes one between train and truck transport.
Technical Paper

Ammonia as a Fuel for SI Engine

2003-10-27
2003-01-3095
Ammonia is a potential alternative fuel that was indeed put into use in Belgium in World War II due to the extreme shortage of diesel. It has a high heating value per unit volume (1.16 × 107 kJ/m3) and its combustion products can be as or more environment-friendly compared to conventional hydrocarbon fuels. This study examined the combustion characteristics of premixed ammonia-air mixtures at atmospheric and elevated conditions which are encountered in SI engine operation. The laminar burning velocity, flame temperature and species distribution were determined using the Lindstedt mechanism in CHEMKIN. A freely propagating flame was assumed to facilitate the investigation. The predicted laminar burning velocity and the flammability limits were compared with experimental values.
Technical Paper

Quantifying Vehicle Emission Factors for Various Ambient Conditions using an On-Road, Real-Time Emissions System

2003-03-03
2003-01-0301
This paper demonstrates vehicle emission factor measurement using an on-board, on-road system and examines the effects of ambient temperature on those emission factors. Vehicle operating parameters, fuel consumption and emissions were measured on-road using a portable measurement system designed for ease of use with a range of vehicles, drivers and driving situations. The results reported here come from repeated trips over a 17.4 km urban / suburban route with a particular driver and vehicle. As such, the emission factors developed here do not represent the current on-road fleet. However, they show the strong influence of actual operating conditions (particularly ambient temperature) and of the vehicle control system's response to non-standard conditions. This leads to an appreciation for on-road testing as a means to illustrate vehicle emission behavior in real conditions and to highlight conditions which may require more detailed study.
Technical Paper

Real-Time, On-Road Measurement of Driving Behavior, Engine Parameters and Exhaust Emissions

2002-05-06
2002-01-1714
Automotive tailpipe emissions are a significant contribution to urban air quality problems.(1) However, it is difficult to quantify the extent of that contribution and to quantify any progress in solving the problem. Emissions inventories are commonly based on vehicle registrations, assumed mileage and a set of emission factors. The emission factors are based on dynamometer testing of selected vehicles undertightly controlled conditions. Actual vehicle operation in any urban area encompasses a wider range of vehicles, operating conditions and ambient conditions. Given the highly tuned nature of current engine management systems, the actual in-use emissions levels can be highly sensitive to non-standard ambient and operating situations.(2,3,4,5) This paper describes an on-board system used to record ambient conditions, driving behavior, vehicle operating parameters, fuel consumption and exhaust emissions.
Technical Paper

A Case Study for Life Cycle Assessment (LCA) as an Energy Decision Making Tool: The Production of Fuel Ethanol from Various Feedstocks

1998-11-30
982205
Life Cycle Analysis (LCA) considers the key environmental impacts for the entire life cycle of alternative products or processes in order to select the best alternative. An ideal LCA would be an expensive and time consuming process because any product or process typically involves many interacting systems and a considerable amount of data must be analysed for each system. Practical LCA methods approximate the results of an ideal analysis by setting limited analysis boundaries and by accepting some uncertainty in the data values for the systems considered. However, there is no consensus in the LCA field on the correct method of selecting boundaries or on the treatment of data set uncertainty. This paper demonstrates a new method of selecting system boundaries for LCA studies and presents a brief discussion on applying Monte Carlo Analysis to treat the uncertainty questions in LCA.
Technical Paper

Uncertainty, Sensitivity and Data Quality Assessment for Life Cycle Value Assessment (LCVA)

1998-02-23
980479
Life Cycle Value Assessment (LCVA) is a decision making tool which considers environmental, economic and/or social aspects for the entire life cycle of a product or process from “cradle-to-grave”. LCVA can be used for a wide range of public policy and business decisions with the analysis being performed at various levels of rigour. By its nature, LCVA utilizes data sets of varying qualities drawn from a wide range of sources. The uncertainties in the input data obviously lead to uncertainties in the results of the LCVA analysis. To establish confidence in an LCVA's recommendations, it is important to consider these uncertainties and incorporate an assessment of uncertainty into the LCVA process. However, the diverse nature of the data sets being used makes it difficult to rigorously establish data uncertainty levels. In addition, the complexity of most life cycle models makes it difficult to trace uncertainty through the analysis process.
Technical Paper

Life Cycle Value Assessment (LCVA) Comparison of Conventional Gasoline and Reformulated Gasoline

1998-02-23
980468
Fuel choices are being made today by consumers, industry and government. One such choice is whether to use reformulated gasoline to replace regular unleaded gasoline. A second choice involves the source of crude oil, with synthetic crude oil from tar sands currently expanding its share of the Canadian supply. Decision makers usually work with the direct economic consequences of their fuel choice. However, they generally lack the knowledge to measure environmental aspects of different fuel systems. This paper uses Life Cycle Value Assessment (LCVA) to demonstrate how the life cycle environmental aspects can be compared for alternative fuel choices. LCVA is an engineering decision making tool which provides a framework for the decision maker to consider the key economic and environmental impacts for the entire life cycle of alternative products or process systems.
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