Source Of Hydrocarbon Emissions Research Articles

An Experimental and Computational Study on Triple Injection Strategies to Reduce Cold Start Diesel Engine Emissions

Abstract The effect of triple injection strategies in a diesel engine to reduce cold start emissions were experimentally and computationally investigated in this work. The experiments were performed using a 1.9 L four-cylinder, turbocharged compression ignition engine with diesel fuel. As a representative of the cold start condition in the diesel engine, a low load condition of 1500 rpm and 2 bar brake mean effective pressure (BMEP) was chosen as the fixed condition for this study. The injection strategy made use of a late post injection to reduce catalyst light-off time. The pilot and main injections are fixed and the post injection timing is swept later into the expansion stroke to increase exhaust enthalpy available to heat the aftertreatment system. To further understand the source of hydrocarbon (HC) emissions from late injections, equivalent experiments were conducted with a mixture of n-heptane and iso-octane that matched the reactivity of the diesel fuel. The mixture of primary reference fuels (i.e., PRF 34) obtained by matching the cetane number (CN) of diesel fuel, showed similar combustion characteristics of diesel, but is much more volatile due to lighter components in the PRF mixture. The increased volatility of PRF 34 suppressed liquid fuel impingement on the cylinder liner, which isolated liner impingement as a possible source of HC emissions. Simulations were also performed for the present engine configuration and operating conditions in a sector mesh using CONVERGE™. The physical properties of diesel fuel were modeled using a five-component surrogate. The chemical kinetics of the diesel fuel were modeled with a reduced n-heptane model. The simulations were able to capture the experimental trends of combustion characteristics and emissions. The HC emissions were observed to increase for both fuels with retarded post injection timings in engine experiments. PRF 34 had comparable HC emissions to diesel experiments, which indicated that the liner impingement is not the main source of the increase in HC emissions. Overmixing of the fuel and air was identified as the major cause of increase in HC emissions. Additionally, exhaust gas recirculation (EGR) also intensified the overmixing phenomenon and thereby increase in HC emissions.

Numerical investigation of natural gas-diesel dual-fuel engine with different piston geometries and radial clearances

Piston crevices are the major source of hydrocarbon emissions for spark ignition engine. It is similar for natural gas-diesel (NG-diesel) dual fuel engine, maybe even worse in high compression ratio and lean burn NG-diesel engine at low load. The aim of this paper is to numerically investigate combustion and methane emissions of YC-6K NG-diesel engine with different radial clearances. Four piston clearances (0.5 mm, 0.76 mm, 1.0 mm and 1.54 mm) and four different piston geometries were employed. Three diesel-spray-orientated (DSO) piston bowls were designed based on diesel injectors of YC-6K with the purpose of supplying more natural gas and air mixture to diesel spray jets, in addition, a protrusion-ring was designed at the bowl rim of DSO pistons to enhance methane flame propagation. The results showed that both in-cylinder pressure and heat release rate (HHR) of all three DSO pistons increased due to higher turbulence kinetic energy comparing to the original piston design (OPD). Methane emissions of pistons with radial clearance of 0.76 mm were lower than that of other radial clearances for DSO pistons.

Red Sea is potent source of hydrocarbon emissions

Red Sea is potent source of hydrocarbon emissions

Contribution Ratio Study of Fuel Alcohol and Gasoline on the Alcohol and Hydrocarbon Emissions of a Gasohol Engine

Methanol (CH3OH) and ethanol (C2H5OH) are generally called alcohol. They can be mixed with gasoline to fuel SI engine. The fuel blends of alcohol and gasoline are named gasohol. Alcohol emission characteristics and the contributions of fuel on hydrocarbon (HC) emission were experimentally investigated on a three-cylinder, electronic controlled, spark ignition JL368Q3 engine when it ran on 10 (v/v) %, 20 (v/v) %, and 85 (v/v) % methanol/gasoline and ethanol/gasoline fuel blends. Experimental results show that, the value of alcohol emission rates (g alcohol emission per kg alcohol fuel, g/kg.) is a decreasing exponential function of exhaust temperature with high correlation; regardless of the alcohol fraction in fuel blends, the CH3OH emission rate is no more than 8%, while that of C2H5OH no more than 35%. The emission rate of nonalcohol HC was one grade higher than the alcohol emission rate; the minimum HC emission rate occurs at middle and high engine loads, it is around 40% for methanol/gasoline blends and about 50% for ethanol/gasoline blends. Gasoline is the main source of HC emission of gasohol engine, methanol contributes no more than 8% while ethanol no more than 25% on HC emission.

Major sources of hydrocarbon emissions in a premixed charge compression ignition engine

Although premixed charge compression ignition (PCCI) combustion engines are praised for potentially high efficiency and clean exhaust, experimental engines built to date emit more hydrocarbons (HCs) and carbon monoxide (CO) than the conventional machines. These compounds are not only strictly controlled components of the exhaust gas of road vehicles but are also an energy loss indicator. The prime objective of this study was to investigate the major sources of the HCs formed in the combustion chamber of an experimental PCCI engine in order to suggest some effective technologies for HC reduction. In this study, to explore the dominant sources of HC emissions in both operation modes, a single cylinder engine was prepared such that it could operate using either conventional diesel combustion or PCCI combustion. Specifically, the contributions of the top-ring crevice volume in the combustion chamber and the bulk quenching of the lean mixture were investigated. To understand the influence of the shape and magnitude of the crevice on HC emissions, the engine was operated with 12 specially prepared pistons with different top-ring crevices installed one after another. The engine emitted proportionally more HCs as the depth of the crevice increased as long as the width remained narrower than the prevailing quench distance. The top-ring-crevice-originated exhaust HCs comprised approximately 31% of the total HC emissions in the baseline condition. In a series of tests to estimate the effects of bulk quench on exhaust HC emissions, intake air was heated from 300K to 400K in steps of 25K. With the intake air heated, HC and CO emissions decreased with a gradually diminishing rate to zero at 375K. In conclusion, the most dominant sources of HC emissions in PCCI engines were the crevice volumes in the combustion chamber and the bulk quenching of the lean mixtures. The key methods for reducing HC emissions in PCCI engines are minimizing crevice volume in the combustion chamber and maximizing intake air temperature allowed based on the permissible NOx level.

Sources of Hydrocarbon Emissions from Low-Temperature Premixed Compression Ignition Combustion from a Common Rail Direct Injection Diesel Engine

Low-temperature premixed compression ignition combustion (PCI) discussed in this study is achieved via late injection timing (close to top dead center) and heavy exhaust gas recirculation (EGR) using ultra low sulfur Swedish diesel fuel (sulfur content less than 15 ppm). PCI obtains a simultaneous decrease in particulate matter (PM) and oxides of nitrogen (NOx), as where injection timing is retarded, as opposed to conventional combustion, where a PM-NOx trade-off is observed. In PCI, hydrocarbon (HC) and carbon monoxide (CO) are increased, and must be removed using aftertreatment. In order to understand the sources of HC from the PCI regime, gas chromatography with a flame ionization detector is employed to perform exhaust HC speciation at three EGR rates and three injection timings. Volatile HC, semi-volatile HC, and CO increase as the injection timing is retarded or EGR is increased. Retarded injection timing or increased EGR reduces peak cylinder bulk temperature and thereby increases the yield of CO and volatile HC (mostly C1–C3). Retarded injection timing or increased EGR also increases ignition delay, which increases over-mixing and causes more mixture to become so lean that combustion ceases and the output of semi-volatile HC species (mostly unburned C10–C12 fuel) is increased. Volatile HC species are increased more than semi-volatile HC species, which results in a shift to a lighter exhaust HC mixture as injection timing is retarded or EGR is increased.

CFD for Simulation of Crosswind on the Efficiency of High Momentum Jet Turbulent Combustion Flames

Industrial flares have been identified as a potential major source of hydrocarbon emissions from chemical and petrochemical plants in the Gulf Coast area. Several studies have shown that crosswind may compromise the expected 98% efficiency level of these units. In order to understand the key variables in flare operation, a 3D simulation has been performed to predict the effect of crosswind on the efficiency of high momentum, turbulent combustion flames by using the commercial software Fluent 6.2. First, a CH4+ air flame was simulated for quiescent conditions and temperature and concentration profiles were compared to experimental data. Simulations were then performed to study how combustion efficiency may be affected by increasing the crosswind velocity. We have also analyzed the effect of crosswind at higher jet velocities. Our results show that high momentum flames are more sensitive to the crosswind problem as the jet velocity increases. The ultimate goal of this model is to obtain a quantitative understanding of how crosswind may affect the operation of industrial flares, a major source of highly reactive volatile organic compound emissions from chemical and petrochemical plants.

Liquid Fuel Impingement on In-Cylinder Surfaces as a Source of Hydrocarbon Emissions From Direct Injection Gasoline Engines

Hydrocarbon (HC) emissions from direct injection gasoline (DIG) engines are significantly higher than those from comparable port fuel injected engines, especially when “late” direct injection (injection during the compression stroke) is used to produce a fuel economy benefit via unthrottled lean operation. The sources of engine-out hydrocarbon emissions for late direct injection are bulk flame quench, low temperatures for post-combustion oxidation, and fuel impingement on in-cylinder walls. An experimental technique has been developed that isolates the wall impingement source from the other sources of HC emissions from DIG engines. A series of steady-state and transient experiments is reported for which the HC emissions due to operation with a premixed charge using a gaseous fuel are compared to those when a small amount of liquid fuel is injected onto an in-cylinder surface and the gaseous fuel flow rate is decreased correspondingly. The steady-state experiments show that wetting any in-cylinder surface dramatically increases HC emissions compared to homogeneous charge operation with a gaseous fuel. The results of the transient fuel injection interrupt tests indicate that liquid-phase gasoline can survive within the cylinder of a fully warmed-up firing engine and that liquid fuel vaporization is slower than current computational models predict. This work supports the argument that HC emissions from DIG engines can be decreased by reducing the amount of liquid fuel that impinges on the cylinder liner and piston, and by improving the vaporization rate of the fuel that is deposited on these surfaces.

Analysis and interpretation of the continuous hourly monitoring data for 26 C 2–C 8 hydrocarbons at 12 United Kingdom sites during 1996

A fully automatic network with 11 urban background and one rural site has been set up and operated successfully in the UK to measure, continuously, hourly concentrations of 26 C 2–C 8 hydrocarbons; the measurements collected form one of the largest data sets of urban hydrocarbon air quality data available anywhere in Europe. The hourly data have been analysed on a site-by-site and hydrocarbon-by-hydrocarbon basis by constructing scatter plots against benzene. From these scatter plots a number of important sources of hydrocarbon emissions have clearly been identified including: motor vehicle exhaust and evaporative emissions, natural gas leakage, petrol station forecourt evaporative emissions and industrial sources. Overall, urban background hydrocarbon air quality is heavily influenced by motor vehicles and the general pattern of relative concentrations has been accurately defined for the United Kingdom as ratios relative to benzene. Comparisons of these concentrations are made with data for other major cities and with European regional data.

Oil Layer as Source of Hydrocarbon Emissions in SI Engines

The role of lubrication oil film on the cylinder liner as a source of hydrocarbon emissions in spark-ignition engines is assessed. First, the “source strength” is examined via an analytical model of the gasoline vapor absorption/desorption process. The solution shows that depending on engine operating conditions, there are three regimes. The process could be (1) limited by the gas side diffusion process, (2) limited by the liquid phase diffusion process, with the absorbed fuel fully penetrating the oil layer thickness (thin oil film regime), and (3) again limited by the liquid phase diffusion process, but with the absorbed fuel penetration depth small compared to the oil layer thickness (thick oil film regime). In regime (1), the source strength (the integrated absorption or desorption flux over one cycle) is proportional to the inverse of the square root of the rpm, but independent of oil layer parameters. In regimes (2), the strength is proportional to the oil film thickness divided by the Henry’s constant. In regime (3), the strength is independent of the oil film thickness, but is proportional to the fuel penetration depth divided by the Henry’s constant. Then, the oxidation of the desorbed fuel (using iso-octane as fuel) is examined with a one-dimensional reaction/diffusion model. The novel feature of the model is that the desorbed fuel is being exposed to the piston crevice hydrocarbon, which is laid along the liner as the piston descends. At stoichiometric conditions, the oxidation of the crevice HC is reduced by the presence of the desorbed HC from the oil layer.

Behavior of a fuel oil during the combustion cycle of a direct injection diesel engine

In-cylinder sampling and analysis of particulate (soot and condensed hydrocarbon species), light hydrocarbons, and gaseous inorganic species has been performed at two positions of a single cylinder direct injection diesel engine by means of a fast sampling valve, in order to follow the behavior of a diesel oil during the engine cycle. It has been shown that the combustion process in a diesel engine proceeds through a preignition phase of heating and vaporization of the injected fuel, which causes the transformation of the fuel components in light gaseous products and oxygenated compounds that rapidly disappear at the ignition. After ignition, the formation of soot has been found, particularly in the high-temperature position, but the formation of soot precursors, i.e., acetylene and combustion-formed polycyclic aromatic hydrocarbons (PAHs), was not in evidence. In whichever phase of the combustion cycle the PAHs are composed of unburned fuel PAHs but in the low-temperature position the PAH percentage increases, as opposed to the high-temperature position, and this can be due to the high resistance of the fuel PAHs to complete oxidation in this temperature condition. At the same time the appearance of high-molecular-weight material of oxygenated character has been found at the low-temperature position. This could derive from the oxidation, perhaps in liquid phase, of the heavy aromatic compounds of the fuel. The chemical analysis of the hydrocarbons collected in the oxidation phase and in the exhaust revealed that unburned fuel, reentraining the sampling zones from wall quenching and ring crevices, is the main source of hydrocarbon emission from the engine.

Measurement of Quenching Layer Thickness by a Thermocouple

Unburned hydrocarbons remaining in a wall quenching layer have been proposed as a major source of hydrocarbon emissions in spark-ignited internal combustion engines. Although quenching layer thickness can be measured by an optical method, this method cannot usually apply to the combustion chambers of spark-ignited engines where flame propagation is very complex. Therefore quenching layer thickness have been often calculated by the data of quenching distances measured by quenching disks or residual gas analysis.In this paper, the direct measurement system of quenching layer thickness by a thermocouple is described. In consequence, it is found that this method is valid to measure directly quenching layer thickness, because the tendency of the data in this experiment agrees well with that of the quenching distances. A quenching layer is separated into two parts. One is a perfect unreaction layer and the other is a partial reaction layer. The perfect unreaction layer thickness which dominates hydrocarbon emissions is about one-fifth of the quenching layer thickness. Hydrocarbon emissions in spark-ignited internal combustion engines can be estimated by this measurement system.

Quench Layer Contribution to Exhaust Hydrocarbons from a Spark-Ignited Engine

INTRODUCTION Hydrocarbons remaining in a wall quench layer have been proposed as a major source of hydrocarbon emissions in spark-ignited internal combustion engines (Daniel and Wentworth, 1962). Additional experiments using wall mounted sampling valves were subsequently carried out by Daniel (1967), Muller and von Watzdorf (1968), Weiss et al. (1979), and Henningsen and Qvale (1980). Our paper presents the results of an experimental study of the quench layer also using a wall mounted sampling valve. The valve was electrohydraulically actuated and had uniquely small leakage and crevice characteristics. Our results do not support the contention that the wall quench layer is a major source of exhaust emissions. Hydrocarbons from other sources, as yet not quantified, such as those emitted from ring crevices, deposits or oil films appear to be likely contributors to exhaust hydrocarbons (Wentworth, 1971; Haskell and Legate, 1972; and Kaiser et al., 1980).

AComparisonof VariousSourcesof AutomotiveEmissions

All normal sources of hydrocarbon emissions from automobiles were investigated. Special emphasis was placed on crankcase fumes and carburetor evaporation losses since much less information is available concerning these emissions. Exhaust emissions were also measured in order to provide a basis for comparison. Consideration was also given to evaporation losses from the fuel tank of an automobile since this factor also has not been investigated in any detail. 4 references, 5 figure, 9 tables.