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Technical Paper

A Phenomenological Model for Soot Formation and Oxidation in Direct-Injection Diesel Engines

The concentration of carbonaceous particulate matter in the exhaust of diesel engines depends on the rates of formation and oxidation of soot in the combustion chamber. Soot forms early in the combustion process when local fuel-rich areas exist, whereas soot oxidation occurs later when more air is entrained into the fuel spray. Based on this understanding, a phenomenological combustion model is established. In the model, the cylinder volume is divided into four zones: a rich fuel spray core, a premixed-burning/burned gas zone, a mixing controlled burning zone and a lean air zone. Soot formation takes place in the mixing controlled burning zone where the local C/O ratio is above the critical value. Soot oxidation occurs in the premixed-burning/burned gas zone as air is entrained. By using a quasi-global chemical reaction scheme, the oxidation of soot particles by different species can be investigated.
Technical Paper

In-Cylinder Measurement of Temperature and Soot Concentration Using the Two-Color Method

Optical fiber probes were used to measure the soot temperature and estimate the soot concentration inside the cylinder of a DI diesel engine. The probes were mounted at various locations on the head of the test engine, and the measurements were performed under different load levels. Using the two-color method, the variations in temperature and soot mass concentration during the combustion process were examined with temporal and spatial resolution. It was observed that soot formation is rapid and is associated with heterogeneity in the early stage of combustion. Moreover, the soot formation mechanism seems to be independent of the engine load. In contrast, soot oxidation is relatively slow. Data obtained at several different load levels are presented, and the effects of various error sources on the accuracy of the measurement technique are also investigated.
Technical Paper

Evaluation of the Hydrogen-Fueled Rotary Engine for Hybrid Vehicle Applications

The hydrogen-fueled engine has been identified as a viable power unit for ultra-low emission senes-hybrid vehicles The absence of carbon in hydrogen fuel eliminates exhaust emissions of CO, CO2, and hydrocarbons, with the exception of small contributions from the combustion of lubricating oil Thus, the only regulated emission of a hydrogen-fueled engine is NOx, and the engine may be optimized to minimize NOx since the usual constraint of the NOx -hydrocarbon trade-off is not applicable Hydrogen-fueled homogeneous charge piston engines have, however, generally suffered from a variety of combustion difficulties, most notably a proclivity to ignition on hot surfaces such as exhaust valves, spark plug electrodes and deposits on combustion chamber walls The Wankel engine is particularly well suited to the use of hydrogen fuel, since its design minimizes most of the combustion difficulties In order to evaluate the possibilities offered by the hydrogen fueled rotary engine, dynamometer tests were conducted with a small (2 2kW) Wankel engine fueled with hydrogen Preliminary results show an absence of the combustion difficulties present with hydrogen-fueled homogenous charge piston engines The engine was operated unthrottled and power output was controlled by quality governing, i.e. by varying the fuel-air equivalence ratio on the lean side of stoichiometric The ability to operate with quality governing is made possible by the wide flammability limits of hydrogen-air mixtures NOx emissions are on the order of 5 ppm for power outputs up to 70% of the maximum attainable on hydrogen fuel Thus, by operating with very lean mixtures, which effectively derates the engine, very low NOx emissions can be achieved Since the rotary engine has a characteristically high power to weight ratio and a small volume per unit power compared to the piston engine, operating a rotary engine on hydrogen and derating the power output could yield an engine with extremely low emissions which still has weight and volume characteristics comparable to a gasoline-fueled piston engine Finally, since engine weight and volume affect vehicle design, and consequently in-use vehicle power requirements, those factors, as well as engine efficiency, must be taken into account in evaluating overall hybnd vehicle efficiency
Technical Paper

Validation Tests for a Fast Response Flame Ionisation Detector for In-Cylinder Sampling Near the Spark Plug

The air/fuel ratio (AFR) is a key contributor to both the performance and emissions of an automotive engine. Its variation between cylinders - and between engine cycles - is of particular importance, especially during throttle transients. This paper explores the use of a fast flame ionisation detector (FFID) to quantify these rapid changes of in-cylinder composition in the vicinity of the spark gap. While this instrument actually measures fuel concentration, its results can be indicative of the AFR behaviour. Others have used the FFID for this purpose, but the planned test conditions placed special demands on the instrument. These made it prudent to explore the limits of its operating envelope and to validate the experimental technique. For in-cylinder sampling, the instrument must always be insensitive to the large pressure changes over the engine cycle. With the wide range of engine loads of interest here, this constraint becomes even more crucial.
Technical Paper

Effect of Engine Operating Variables and Piston and Ring Parameters on Crevice Hydrocarbon Emissions

A study was performed to determine the effects of engine operating variables and piston and ring parameters on the crevice hydrocarbon emissions from a spark-ignition engine. Natural gas was used as the test fuel in an effort to isolate crevice mechanisms as the only major source of unburned hydrocarbons in the test engine's exhaust. The largest of the in-cylinder crevices, the piston ring pack crevices, were modified, both in size and accessibility, by altering the piston top land height and the number of piston rings and their end gaps. Each piston and ring configuration was subjected to a series of test sweeps of engine operating variables known to affect exhaust hydrocarbon emissions. None of the physical crevice modifications had any significant effect on the level of the exhaust hydrocarbon emissions, although the cycle-to-cycle repeatability of these emissions, measured with a fast hydrocarbon analyzer, was found to vary between the different configurations.
Technical Paper

Operating Parameter Effects on the Speciated Hydrocarbon Emissions from a Natural Gas Fueled Engine

The effects of engine operating parameters on the speciated engine-out hydrocarbon emissions from a natural gas fueled spark ignition 16 valve four-cylinder engine were examined. Total hydrocarbon emissions were dominated by methane, the main component of natural gas. The non-methane hydrocarbons consisted primarily of ethane, ethene, and acetylene. Except for changes in the fuel-air equivalence ratio rich of the stoichiometric condition, emissions of unsaturated species were found to be less sensitive to engine operating parameters than were the fuel components. A single species, ethene, dominated the engine-out hydrocarbon reactivity, accounting for over 80% of the NMHC reactivity.
Technical Paper

Examination of Charge Dilution with EGR to Reduce NOx Emissions from a Natural Gas-Fuelled 16 Valve DOHC Four-Cylinder Engine

Charge dilution is commonly used to reduce emissions of nitrogen oxides (NOx) from internal combustion engine exhaust gas. The question of whether to use air or exhaust gas recirculation (EGR) as a charge diluent for the natural gas-fuelled test engine is addressed first. The decision to use EGR is based on the potentially lower NOx and unburned hydrocarbon emissions that could be achieved if a three-way catalyst were applied to the engine. The effect of EGR on the spark advance for maximum brake torque (MBT), NOx, and unburned hydrocarbon emissions is then examined in detail. The effect on fuel efficiency is discussed briefly.
Technical Paper

Engine Operating Parameter Effects on the Speciated Aldehyde and Ketone Emissions from a Natural Gas Fuelled Engine

Measurements were taken of the speciated aldehyde and ketone exhaust emissions from a modern four-cylinder engine fuelled with natural gas. The effect on these emissions of varying the engine operating parameters spark timing, exhaust gas recirculation rate, engine speed, and fuel/air equivalence ratio was examined. The influence of these operating parameters on the complete reactivity-weighted emissions with natural gas fuelling is predicted. With stoichiometric fuel/air mixtures, both the total hydrocarbons and formaldehyde emissions declined with increasing exhaust gas temperature and increasing in-cylinder residence time, suggesting that formaldehyde burn-up in the exhaust process largely controls its emissions levels. Closer examination of the aldehyde emissions shows they follow trends more like those of the non-fuel, intermediate hydrocarbon species ethane and acetylene, than like the trends of the fuel components methane and ethane.
Technical Paper

Exhaust Emission and Energy Consumption Effects from Hydrogen Supplementation of Natural Gas

An experiment was conducted to evaluate the efficiency and emissions of an engine fuelled with a mixture of natural gas and approximately 15% hydrogen by volume. This mixture, called Hythane™, was compared with natural gas fuel using engine efficiency and engine-out emissions at various engine operating conditions as the basis of comparison. Throughout most of the experiment, fuel mixtures were slightly rich of stoichiometry. It was found that at low engine loads, using the same spark timing, engine efficiency increased under HythaneTM fuelling but at higher engine loads, natural gas and Hythane™ had the same efficiency. At low engine speed and load conditions with the same spark timing, engine-out total hydrocarbon (THC) emissions were lower for Hythane™ fuelling. When compared on a carbon specific basis, however, natural gas hydrocarbon emissions were lower. At some test conditions, engine-out carbon monoxide (CO) emissions were lower under Hythane™.
Technical Paper

Effect of Closed Loop Fuel Control System Characteristics on Emissions from a Natural Gas-Fueled Engine

Some current aftermarket natural gas closed loop carburetion systems use an integral control strategy to maintain a fuel-air equivalence ratio centered in the peak conversion window of a three-way catalytic converter. Fuel control system performance under steady-state engine operating conditions can be characterized by the time-averaged value of the fuel-air equivalence ratio, the rich and lean excursion limits, and a skewness parameter that represents the non-symmetry of the time varying fuel-air equivalence ratio about the control value (ϕaverage). Using a representative aftermarket feedback control system, the effect of these parameters on the exhaust emissions of a natural-gas fueled four-cylinder engine has been investigated. In addition, the effect of EGO sensor characteristics on control system performance has been examined.
Technical Paper

Effect of Increasing Compression Ratio in a Light-Duty Natural Gas-Fueled Engine on Efficiency and Emissions

As a result of CAFE (corporate average fuel economy) requirements, the trend in passenger car engine design is to smaller displacement engines of higher specific output which provide reductions in vehicle driving cycle fuel consumption without an accompanying decrease in maximum power output. Design features such as four valves per cylinder and compact combustion chambers give these engines significantly different combustion characteristics than traditional pushrod OHV (overhead valve) engines. In general, their combustion chambers are fast burning, enabling the use of higher compression ratios without knock on unleaded gasoline. Since fuel consumption decreases with increasing compression ratio, and since natural gas has a substantially higher octane rating than the best unleaded gasoline, it would appear to be desirable to operate with even higher compression ratios in a dedicated natural gas engine.
Technical Paper

Bluff-Body Stabilized Glow Plug Ignition of a Methanol-Fueled IDI Diesel Engine

Methanol, in common with other alternative fuels including natural gas and LPG, has autoignition characteristics which are poorly suited for use in compression ignition engines. Some sort of ignition assist has proven to be necessary. Considerable work has been carried out with hot surface (glow plug) ignition. The geometric relationship between the fuel injection nozzle and the glow plug is critical to achieving high efficiency and low emissions. Moreover, it is difficult to establish a single geometry which provides reliable ignition and stable operation over the entire range of engine speeds and loads. The work described in this paper investigated extending the range of operation of a particular glow plug/fuel injection nozzle geometry by placing the glow plug in the wake of a bluff body. Bluff-body flame stabilization is a well-known technique in continuous combustors. Experiments were carried out in a single-cylinder CFR cetane rating engine fueled with methanol.
Technical Paper

Impact of Powertrain Type on Potential Life Cycle Greenhouse Gas Emission Reductions from a Real World Lightweight Glider

This study investigates the life cycle greenhouse gas (GHG) emissions of a set of vehicles using two real-world gliders (vehicles without powertrains or batteries); a steel-intensive 2013 Ford Fusion glider and a multi material lightweight vehicle (MMLV) glider that utilizes significantly more aluminum and carbon fiber. These gliders are used to develop lightweight and conventional models of internal combustion engine vehicles (ICV), hybrid electric vehicles (HEV), and battery electric vehicles (BEV). Our results show that the MMLV glider can reduce life cycle GHG emissions despite its use of lightweight materials, which can be carbon intensive to produce, because the glider enables a decrease in fuel (production and use) cycle emissions. However, the fuel savings, and thus life cycle GHG emission reductions, differ substantially depending on powertrain type. Compared to ICVs, the high efficiency of HEVs decreases the potential fuel savings.
Technical Paper

Heavy Duty Diesel Engine Modeling with Layered Artificial Neural Network Structures

In order to meet emissions and power requirements, modern engine design has evolved in complexity and control. The cost and time restraints of calibration and testing of various control strategies have made virtual testing environments increasingly popular. Using Hardware-in-the-Loop (HiL), Volvo Penta has built a virtual test rig named VIRTEC for efficient engine testing, using a model simulating a fully instrumented engine. This paper presents an innovative Artificial Neural Network (ANN) based model for engine simulations in HiL environment. The engine model, herein called Artificial Neural Network Engine (ANN-E), was built for D8-600 hp Volvo Penta engine, and directly implemented in the VIRTEC system. ANN-E uses a combination of feedforward and recursive ANNs, processing 7 actuator signals from the engine management system (EMS) to provide 30 output signals.
Technical Paper

Emissions from Compression Ignition Engines with Animal-Fat-Derived Biodiesel Fuels

Biodiesel and other renewable fuels are of interest due to their impact on energy supplies as well as their potential for carbon emissions reductions. Waste animal fats from meat processing facilities, which would otherwise be sent to landfill, have been proposed as a feedstock for biodiesel production. Emissions from biodiesel fuels derived from vegetable oils have undergone intense study, but there remains a lack of data describing the emissions implications of using animal fats as a biodiesel feedstock. In this study, emissions of NOx, unburned hydrocarbons and particulate matter from a compression ignition engine were examined. The particulate matter emissions were characterized using gravimetric analysis, elemental carbon analysis and transmission electron microscopy. The emissions from an animal fat derived B20 blend were compared to those from petroleum diesel and a soy derived B20 blend.
Technical Paper

Modelling and Optimization of Plug Flow Mufflers in Emission Control Systems

Large-scale emergency or off-grid power generation is typically achieved through diesel or natural gas generators. To meet governmental emission requirements, emission control systems (ECS) are required. In operation, effective control over the generator’s acoustic emission is also necessary, and can be accomplished within the ECS system. Plug flow mufflers are commonly used, as they provide a sufficient level of noise attenuation in a compact structure. The key design parameter is the transmission loss of the muffler, as this dictates the level of attenuation at a given frequency. This work implements an analytically decoupled solution, using multiple perforate impedance models, through the transfer matrix method (TMM) to predict the transmission loss based on the muffler geometry. An equivalent finite element model is implemented for numerical simulation. The analytical results and numerical results are then evaluated against experimental data from literature.
Technical Paper

An Experimental Investigation into the Characteristics of a Fast-Response Flame Ionization Detector for In-Cylinder Sampling

The Cambustion fast-response flame ionization detector (FFID) has been successfully used for instantaneous exhaust port hydrocarbon (HC) concentration measurement in IC engines for a decade. Measurements of in-cylinder HC concentration have also been made, but these present greater challenge. As the sample transit time and the time constant of the system always change when the sampling pressure is changed, it is necessary to investigate the characteristics of the system before it was used for in-cylinder sampling. A unique method was designed to study the influence of the diameter and length of the transfer sample line and the operating parameters of the FFID on the transit time and time constant. A database of transit time and time constant was built up for different simulated in-cylinder pressures. The database can be used for correcting eventual in-cylinder HC concentration measurement.
Technical Paper

Application of Nonlinear Transformations to A/F Ratio and Speed Control in an IC Engine

This paper presents the first application of the global feedback linearization method to an internal combustion (IC) engine. Through the application of this nonlinear control technique, the nonlinear coupled dynamics of the IC engine are globally linearized and decoupled. This represents a significant advance over previously published control approaches which rely on locally linearized dynamic models. With the IC engine dynamics globally linearized and decoupled, outer-loop controllers can be readily designed using simple linear tracking controller design methods, leading to very good dynamic response of three key IC engine outputs, air/fuel ratio, engine speed and manifold air pressure. In this paper, a standard IC engine model from the literature is first transformed to a controllable canonical form, required for the application of the global feedback linearization methods.
Technical Paper

The Effect of Oxygenated Additives on Soot Precursor Formation in a Counterflow Diffusion Flame

A counter–flow propane/air diffusion flame (ϕ= 1.79) is used for a fundamental analysis of the effects of oxygenated additives on soot precursor formation. Experiments are conducted at atmospheric pressure using Gas Chromatography for gas sample analysis. The oxygenated additives dimethyl carbonate (DMC) and ethanol are added to the fuel keeping the total volumetric fuel flow rate constant. Results show 10 vol% DMC significantly reduces acetylene, benzene, and other flame pyrolysis products. Ethanol (10 vol%) shows, instead, more modest reductions. Peak acetylene and benzene levels decrease as the additive dosage increases for both DMC and ethanol. The additive's effect on the adiabatic flame temperature and the fuel stream carbon content does not correlate significantly with acetylene levels. However, there does appear to be a linear relationship between acetylene concentrations and both the additive's oxygen and C–C bond content.
Technical Paper

Instantaneous In-Cylinder Hydrocarbon Concentration Measurement during the Post-Flame Period in an SI Engine

Crevices in the combustion chamber are the main source of hydrocarbon (HC) emissions from spark ignition (SI) engines fuelled by natural gas (NG). Instantaneous in-cylinder and engine exhaust port HC concentrations were measured simultaneously using a Cambustion HFR400 fast response flame ionization detector (FRFID) concentrated on the post-flame period. The raw data was reconstructed to account for variation in the FFRID sample transit time and time constant due to fluctuating in-cylinder pressure. HC concentration development during the post-flame period is discussed. Comparison is made of the post-flame in-cylinder and exhaust port HC concentrations under different engine operating conditions, which gives a better understanding of the mechanism by which HC emissions form from crevices in SI engines.