Search Results

Five small two-stroke engine designs were tested at different air/fuel ratios, under steady state and transient cycles. The effects of combustion chamber design, carburetor design, lean burning, and fuel composition on performance, hydrocarbon and carbon monoxide emissions were studied. All tested engines had been designed to run richer than stoichiometric in order to obtain satisfactory cooling and higher power. While hydrocarbon and carbon monoxide emissions could be greatly reduced with lean burning, engine durability would be worsened. However, it was shown that the use of a catalytic converter with acceptably lean combustion was an effective method of reducing emissions. Replacing carburetion with in-cylinder fuel injection in one of the engines resulted in a significant reduction of hydrocarbon and carbon monoxide emissions.

Engine performance under transients is greatly affected by the fuel behavior in the induction systems. To better understand the fuel behavior, a computer model has been developed to study the one-dimensional coupled heat and mass transfer processes occurring during the transient evaporation of liquid fuel from a heated surface into stagnant air. The energy and mass diffusion equations are solved simultaneously to yield the transient temperatures and species concentrations using a modified finite difference technique. The numerical technique is capable of solving the coupled equations while simultaneously tracking the movement of the evaporation interface. Evaporation results are presented for various initial film thicknesses representing typical puddle thicknesses for multi-point fuel injection systems using heptane, octane, and nonane pure hydrocarbon fuels.

A group of GM C-2500 heavy-duty and GM C-1500 light-duty trucks were modified to bi-fuel compressed natural gas (CNG)/gasoline and liquefied petroleum gas (LPG)/gasoline vehicles. The fuel management systems used for different model year vehicles were introduced. The Alternative Fuel Technology (AFT) System used for 1997 GM C-2500 trucks is discussed in detail. AFT is an automatic switching bi-fuel system which is able to control fuel flow rate, spark timing, and EGR, and perform On-Board Diagnostics (OBD-II). The exhaust emissions of carbon monoxide (CO), total hydrocarbon (HC) and oxides of nitrogen (NOx) were measured using dilute sampling techniques. The vehicles tested were operated on a chassis dynamometer and run on the Federal Test Procedure (FTP) Urban Schedule.

Engine out (feedgas) emissions control during cold start operations has been a major technical challenge since mandated LEV/ULEV/SULEV/PZEV regulation compliance. Cold start emissions contribute to more than 85% of total emissions in a FTP test. Unburned Hydrocarbons are mostly generated during cold starts due to a rich Air/fuel ratio strategy. Cold intake and cylinder wall surfaces do not provide a quick vaporization bed for the rich fuel, therefore un-vaporized and unburned fuel result in excessive tailpipe emissions. Utilizing fuel vapor during cold starts reduces the Hydrocarbon (HC) emissions level and minimizes the transient fuel effect process. A vapor management system must function to control the Air-to-fuel ratio of the intake charge during “cold-starts”, idle, and drive-away, or until catalyst lights off to a desired level.

Despite remarkable progress made over the past 30 years, automobiles continue to be a major source of hydrocarbon emissions. The objective of this study is to evaluate whether variable exhaust valve opening (EVO) and exhaust valve closing (EVC) can be used to reduce hydrocarbon emissions. An automotive gasoline engine was tested with different EVO and EVC timings under steady-state and start-up conditions. The first strategy that was evaluated uses early EVO with standard EVC. Although exhaust gas temperature is increased and catalyst light-off time is reduced, the rapid drop in cylinder temperature increases cylinder-out hydrocarbons to such a degree that a net increase in hydrocarbon emissions results. The second strategy that was evaluated uses early EVO with early EVC. Early EVO reduces catalyst light-off time by increasing exhaust gas temperature and early EVC keeps the hydrocarbon-rich exhaust gas from the piston crevice from leaving the cylinder.

A FeCrAlloy mesh-type catalyst has been used to reduce hydrocarbons (HC) and carbon monoxide (CO) emissions from a 4-stroke HCCI engine. Significant for the HCCI engine is a high compression ratio and lean mixtures, which leads to a high efficiency, low combustion temperatures and thereby low NOx emissions, <5 pmm, but also low exhaust temperatures, around 300°C. It becomes critical to: 1. Ensure that the HCCI-combustion generates as low HC emissions as possible, this can be done by very precise control of engine inlet conditions and, if possible, compression ratio. 2. Ensure that the exhaust temperature is high enough, without loosing efficiency or producing NOx; in order to get an oxidizing catalyst to work. 3. Select proper catalyst material for the catalyst so that the exhaust temperature can be as low as possible.

An experimental and theoretical study of the effect of thermal barriers and catalytic coatings in a Homogeneous Charge Compression Ignition (HCCI) engine has been conducted. The main intent of the study was to investigate if a thermal barrier or catalytic coating of the wall would support the oxidation of the near-wall unburned hydrocarbons. In addition, the effect of these coatings on thermal efficiency due to changed heat transfer characteristics was investigated. The experimental setup was based on a partially coated combustion chamber. The upper part of the cylinder liner, the piston top including the top land, the valves and the cylinder head were all coated. As a thermal barrier, a coating based on plasma-sprayed Al2O3 was used. The catalytic coating was based on plasma-sprayed ZrO2 doped with Platinum. The two coatings tested were of varying thickness' of 0.15, 0.25 and 0.6 mm. The compression ratio was set to 16.75:1.

A key element to achieving vehicle emission certification for most light-duty vehicles using spark-ignition engine technology is prompt catalyst warming. Emission mitigation largely does not occur while the catalyst is below its “light-off temperature”, which takes a certain time to achieve when the engine starts from a cold condition. If the catalyst takes too long to light-off, the vehicle could fail its emission certification; it is necessary to minimize the catalyst warm up period to mitigate emissions as quickly as possible. One technique used to minimize catalyst warm up is to calibrate the engine in such a way that it delivers high temperature exhaust. At idle or low speed/low-load conditions, this can be done by retarding spark timing with a corresponding increase in fuel flow rate and / or leaning the mixture. Both approaches, however, encounter limits as combustion stability degrades and / or nitrogen oxide emissions rise excessively.

Gasoline fuels are complex mixtures which consist of more than 200 different hydrocarbon species. In order to decrease the chemical and physical complexity, oxygenated surrogate components were used to enhance the fundamental understanding of partially premixed combustion (PPC). The ignition quality of a fuel is measured by octane number. There are two methods to measure the octane number: research octane number (RON) and motor octane number (MON). In this paper, RON and MON were measured for a matrix of n-heptane, isooctane, toluene, and ethanol (TERF) blends spanning a wide range of octane number between 60.6 and 97. First, regression models were created to derive RON and MON for TERF blends. The models were validated using the standard octane test for 17 TERF blends. Second, three different TERF blends with an ignition delay (ID) of 8 degrees for a specific operating condition were determined using a regression model.

In the engine community, gasoline compression ignition (GCI) engines are at the forefront of research and efforts are being taken to commercialize an optimized GCI engine in the near future. GCI engines are operated typically at Partially Premixed Combustion (PPC) mode as it offers better control of combustion with improved combustion stability. While the transition in combustion homogeneity from convectional Compression Ignition (CI) to Homogenized Charge Compression Ignition (HCCI) combustion via PPC has been comprehensively investigated, the physical and chemical effects of fuel on GCI are rarely reported at different combustion modes. Therefore, in this study, the effect of physical and chemical properties of fuels on GCI is investigated. In-order to investigate the reported problem, low octane gasoline fuels with same RON = 70 but different physical properties and sensitivity (S) are chosen.

Global warming and the increasingly stringent emission regulations call for alternative combustion techniques to reduce CO2 emissions. Oxy-fuel combustion is one of those techniques since the combustion products are easily separated by condensing the water and storing CO2. A problem associated with the burning of fuel using pure oxygen as an oxidant is that it results in high adiabatic flame temperature. This high flame temperature is decreased by introducing a thermal buffer to the system. A thermal buffer in this context is any gas that does not participate in combustion but at the same time absorbs some of the released heat and thus decreases the temperature of the medium. Many experiments have been conducted to study oxy-fuel combustion in ICE using noble gases as thermal buffers. However, those experiments focused on using hydrogen as a fuel to avoid any build-up of CO2 in the system.

Exhaust gas recirculation (EGR) coolers are commonly used in diesel engines to reduce the temperature of recirculated exhaust gases in order to reduce NOX emissions. Engine coolant is used to cool EGR coolers. The presence of a cold surface in the cooler causes fouling due to particulate soot deposition, condensation of hydrocarbon, water and acid. Fouling experience results in cooler effectiveness loss and pressure drop. In this study, possible soot deposition mechanisms are discussed and their orders of magnitude are compared. Also, probable removal mechanisms of soot particles are studied by calculating the forces acting on a single particle attached to the wall or deposited layer. Our analysis shows that thermophoresis in the dominant mechanism for soot deposition in EGR coolers and high surface temperature and high kinetic energy of soot particles at the gas-deposit interface can be the critical factor in particles removal.

EGR coolers are mainly used on diesel engines to reduce intake charge temperature and thus reduce emissions of NOx and PM. Soot and hydrocarbon deposition in the EGR cooler reduces heat transfer efficiency of the cooler and increases emissions and pressure drop across the cooler. They may also be acidic and corrosive. Fouling has been always treated as an approximate factor in heat exchanger designs and it has not been modeled in detail. The aim of this paper is to look into fouling formation in an EGR cooler of a diesel engine. A 1-D model is developed to predict and calculate EGR cooler fouling amount and distribution across a concentric tube heat exchanger with a constant wall temperature. The model is compared to an experiment that is designed for correlation of the model. Effectiveness, mass deposition, and pressure drop are the parameters that have been compared. The results of the model are in a good agreement with the experimental data.