Cold Start Period Research Articles

Study of spark ignition engine fueled with methanol/gasoline fuel blends

A 3-cylinder port fuel injection engine was adopted to study engine power, torque, fuel economy, emissions including regulated and non-regulated pollutants and cold start performance with the fuel of low fraction methanol in gasoline. Without any retrofit of the engine, experiments show that the engine power and torque will decrease with the increase fraction of methanol in the fuel blends under wide open throttle (WOT) conditions. However, if spark ignition timing is advanced, the engine power and torque can be improved under WOT operating conditions. Engine thermal efficiency is thus improved in almost all operating conditions. Engine combustion analyses show that the fast burning phase becomes shorter, however, the flame development phase is a little delay. When methanol/gasoline fuel blends being used, the engine emissions of carbon monoxide (CO) and hydrocarbon (HC) decrease, nitrogen oxides (NO x ) changes little prior to three-way catalytic converter (TWC). After TWC, the conversion efficiencies of HC, CO and NO x are better. The non-regulated emissions, unburned methanol and formaldehyde, increase with the fraction of methanol, engine speed and load, and generally the maximum concentrations are less than 200 ppm. Experimental tests further prove that methanol and formaldehyde can be oxidized effectively by TWC. During the cold start and warming-up process at 5 °C, with methanol addition into gasoline, HC and CO emissions decrease obviously. HC emission reduces more than 50% in the first few seconds (cold start period) and nearly 30% in the following warming-up period, CO reduces nearly 25% when the engine is fueled with M30. Meanwhile, the temperature of exhaust increases, which is good to activate TWC.

MIMO CONTROL FOR AUTOMOTIVE COLDSTART

The problem of controlling spark ignition engine emissions during the coldstart period is addressed by designing a model-based MIMO sliding mode controller. The task of the controller is to track a given set of desired profiles of engine-out hydrocarbon (HC) emissions and catalyst temperature using spark timing and fuel injection rate as the inputs. The throttle is not used as a control input. The models used for control design are presented in another paper submitted to the same conference. Different profiles of desired engine-out raw HC and catalyst temperatures are used to analyze the coldstart control problem. Simulation results illustrate the trade-off between low raw HC and fast catalyst ligh-off. It was found that the controller tracks the desired profiles as long as the inputs were not saturated. The controller presented here could be used as a tool to investigate the optimal input profiles. Experiments are being carried out to validate the simulations. Submitted to Fifth IFAC Symposium on Advances in Automotive Control

Control of hydrocarbon cold-start emissions: A search for potential adsorbents

A principle of single-file diffusion has been successfully employed to control automotive hydrocarbon (HC) emissions particularly during the cold-start period. Temperature programmed desorption technique of toluene and ethylene, as probe sorbates, was employed to screen a series of as synthesized one-dimensional molecular sieves as potential HC traps. Ethylene was found to be trapped to varying degrees by the larger toluene molecules within the 1-D pores of the synthesized samples. In particular, ZSM-12 and SAPO-5 showed superior trapping performance for both sorbates. ZSM-12 was selected as a better candidate because of its higher temperature of desorption maximum for ethylene (150 °C), which is comparable to the light-off temperature of automotive catalytic converter. It was also found that this adsorbent was stable up to the desired temperature of operation i.e., 800 °C, however with some reduction in ethylene trapping capacity.

CFD simulation of the effect of upstream flow distribution on the light-off performance of a catalytic converter

This paper describes the evolutions of the distributions of temperature and concentration in the monolith during the cold-start period and the effects of the flow distributions in the monolith on the performance of a catalytic converter using numerical simulation. The effects of the flow distributions on the light-off, warm-up performance and the temporal variation of the solid temperature were studied through numerical simulation. The following conclusions were obtained from the predicted light-off curves and the steady conversion efficiency: (1) The light-off time increases and the total outlet conversion efficiency reduces as the flow uniformity index decreases, which is in good agreement with experimental results. (2) The conversion efficiency decreases due to the reduction of residence time caused by the increase of the velocity as the radius is reduced. The analyses on the distribution of temperature in the monolith show that the temperatures of the solid in the area near the front face of the substrate rise as the radius increases, and the radial gradient of the temperature of the solid becomes greater as the flow uniformity index decreases. An experiment on the flow distribution in a catalytic converter with a honeycomb spherical arc was conducted. Experimental results show that the flow distribution in the monolith can be improved greatly by installing the honeycomb spherical arc in the tapered inlet header with a penalty of a relatively small increase of pressure drop.

DYNAMIC SURFACE CONTROL OF ENGINE EXHAUST HYDROCARBONS AND CATALYST TEMPERATURE FOR REDUCED COLDSTART EMISSIONS

Almost three quarters of the hydrocarbon (HC) emissions emitted by an automobile in a typical drive-cycle are produced during the first three minutes of its operation called the coldstart period. In this paper, we propose a way to decrease cold start emissions. A Model-Based paradigm is used to aid the generation of an efficient controller. The controller is built around a mean value engine model and a simplified catalyst model characterized by thermal dynamics, oxygen storage and static efficiency curves. It is shown that the control of engine-out exhaust gas temperature for faster catalyst light-off could be detrimental to the catalyst. A control scheme comprising engine-out hydrocarbon emissions control and catalyst temperature control through dynamic surface control is developed to reduce the tailpipe emissions. It is shown that reduced tailpipe emissions can be achieved without the risk of damaging the catalyst.

A SIMPLIFIED COLDSTART CATALYST THERMAL MODEL TO REDUCE HYDROCARBON EMISSIONS

It is a well-known phenomenon that the bulk of hydrocarbon emissions emitted from internal combustion engines occurs during the coldstart period, thus necessitating new control strategies to reduce hydrocarbon emissions. A simplified thermal model of the catalytic converter during coldstart is developed, employing thermal dynamics, oxygen storage and static conversion curves. It is subsequently shown that oxygen storage does not play a significant role during coldstart. An empirical parametrization of the catalyst efficiency using Wiebe profiles is proposed to capture general conversion trends of the catalyst. Finally it is shown that the ability of the catalyst to reduce hydrocarbon emissions during coldstart is dominated by its thermal behavior and ability to rapidly achieve lightoff. Model predictions are compared to experimental results for catalyst warmup with good agreement.

Adsorption characteristics of HCA(Hydrocarbon Adsorber) catalysts for hydrocarbon and NOx, removals under cold-start engine conditions

To meet the SULEV (Super Ultra Low Emission Vehicle) regulations, we have focused on the utilization of HCA (Hydrocarbon Adsorber) in order to adsorb the excess hydrocarbons emitted during a period of engine cold-start. As main recipes of HCA materials, many types of zeolite as well as a combination of alumina and precious metals were used. Representative physico-chemical factors of zeolite such as acidic and hydrophobic properties have been characterized and tried to find the optimum recipe of HCA materials. Among the acid properties of zeolites, the Si/ Al ratio has been found to be the most important factor to achieve higher hydrocarbon adsorption capacity.

Acetylene and carbon monoxide oxidation over a Pt/Rh/CeO 2/ γ-Al 2O 3 automotive exhaust gas catalyst: kinetic modelling of transient experiments

The transient kinetics of acetylene (C 2H 2) conversion by oxygen over a commercial Pt/Rh/CeO 2/ γ-Al 2O 3 three-way catalyst have been modelled. Experiments to validate the model were carried out in a fixed-bed reactor with two separate inlets, enabling alternate feeding of acetylene and oxygen. Frequencies of feed composition cycling up to 1/6 Hz were applied. The experimental conditions resemble the cold-start period of an Otto engine. Two types of adsorbed acetylene species seem to exist. A selective catalyst deactivation for oxygen adsorption, due to deposition of carbonaceous deposits, was found. Ceria proved to have a significant influence on the acetylene oxidation. A kinetic model was developed for the conversion of acetylene to carbon monoxide, based on elementary reaction steps. This model was combined with the published kinetics for transient carbon monoxide oxidation to carbon dioxide over the same catalyst (Nibbelke, R. H., Chapman, M. A. J., Hoebink, J. H. B. J., & Marin, G. B. (1997). Kinetic study of the CO oxidation over Pt/V-Al 2O 3 and Pt/Rh/ CeO 2/ γ−Al 2O 3 in the presence of H 2O and CO 2. Journal of Catalysis, 171, 358–373.), in order to describe the total oxidation of acetylene quantitatively. The combined model is able to describe the results of the transient experiments on simultaneous acetylene and carbon monoxide oxidation. During a transient, both acetylene and carbon monoxide react mainly in a front moving through the reactor, carbon monoxide hardly influencing the acetylene oxidation.

Transient Kinetic Modeling of the Ethylene and Carbon Monoxide Oxidation over a Commercial Automotive Exhaust Gas Catalyst

The transient kinetics of ethylene oxidation by oxygen over a commercial Pt/Rh/CeO2/γ-Al2O3 three-way catalyst were modeled. Experiments were carried out in a fixed-bed microreactor with two separate inlets, enabling alternate feeding of ethylene and oxygen with frequencies up to 1/4 Hz. The experimental conditions resemble the cold-start period of an Otto engine in a car. Two types of adsorbed ethylene species seem to exist. A selective catalyst deactivation for oxygen adsorption, due to deposition of carbonaceous species, was found. A kinetic model was developed, based on elementary reaction steps, that allows one to describe the experiments quantitatively. Furthermore, this model was combined with the published model for transient carbon monoxide oxidation over the same catalyst,1 which enables one to predict the results of simultaneous ethylene and carbon monoxide oxidation. Both components react in rather distinct zones, with ethylene being converted only when carbon monoxide oxidation is almost comp...

A Fuel-Based Approach to Estimating Motor Vehicle Cold-Start Emissions

ABSTRACT The temporary ineffectiveness of motor vehicle emission controls at startup causes emission rates to be much higher for a short period after starting than during fully warmed, or stabilized, vehicle operation. Official motor vehicle emission inventories estimate that excess emissions during cold-start operation contribute a significant fraction of all hydrocarbon, carbon monoxide (CO), and nitrogen oxide (NOx) emissions from California vehicles. In an effort to verify these estimates under real-world conditions, vehicle emissions were measured in an underground parking garage in Oakland, CA, during March 1997. Hot stabilized emissions were measured as vehicles arrived at the garage in the morning, and cold-start emissions were measured as vehicles exited in the afternoon; the incremental, or excess, emissions associated with vehicle starting were calculated by difference. Composite emissions from ~135 vehicles were sampled during each of six morning and six afternoon periods. Measured stabilized exhaust emissions were 19 ± 2 g nonmethane hydrocarbons (NMHC), 223 ± 17 g CO, and 8.6 ± 1.3 g NOx per gal of gasoline consumed. Cold-start emissions of 69 ± 2 g NMHC/gal, 660 ± 15 g CO/gal, and 27.8 ± 1.2 g NOx/gal were measured for vehicles spending an average of ~60 sec in the garage after starting in the afternoon. Using second-by-second emissions data from California's light-duty vehicle surveillance program, average fuel use during cold start was estimated to be ~0.07 gal, and the cold-start period was estimated to last for ~200 sec. When cold-start emission factors measured in the garage were scaled to represent the full 200-sec cold-start period, incremental start emission factors of 2.1 g NMHC, 16 g CO, and 2.1 g NOx per vehicle start were calculated. These emission factors are lower than those used by California's motor vehicle emission inventory model (MVEI 7G) by 45% for NMHC, 65% for CO, and 12% for NOx. This suggests that the importance of cold-start emissions may be overstated in current emission inventories. Overall, the composition of volatile organic compound (VOC) emissions measured during cold start was similar to that of hot stabilized VOC emissions. However, the weight fractions of unburned fuel and acetylene were higher during cold start than during hot stabilized driving.

5357908 Fuel modification method and apparatus for reduction of pollutants emitted from internal combustion engines

A method for controlling exhaust gas emissions from an engine (16) includes extracting a light distillate fuel (Fd) from conventional gasoline or other liquid hydrocarbon fuel and supplying the engine with the light distillate fuel during an initial operation period of the engine. This reduces the oxidizable pollutants in the engine exhaust during a cold-start period before a catalytic converter (22) used to abate pollutants in the engine exhaust gases has not yet attained its operating temperature. After the catalytic converter (22) has been sufficiently heated, the fuel supply to the engine (16) is switched to gasoline or other liquid hydrocarbon fuel. Both the distillate fuel (Fd) and the liquid hydrocarbon fuel may be passed through a heated cracking catalyst bed (30) to crack the fuel fed to the engine.

Preparation, activity and durability of promoted platinum catalysts for automotive exhaust control

The effects of the addition of calcia, ceria and lanthana to alumina-supported platinum catalysts on the simultaneous control of hydrocarbon, carbon monoxide and nitrogen oxide automobile emissions (three-way catalyst behaviour) were analyzed. The activity of the prepared samples was determined with steady-state, reducing and oxidizing, simulated feedstreams as well as with a cycled oxidizing-reducing feedstream averaged at the stoichiometric conditions which resembled the exhaust air/fuel fluctuations in a closed-loop emission control system. Activity of the catalysts was also analyzed after conducting accelerated thermal and chemical ageing in order to test their durability. Under normal operating conditions of the automobile engine, Pt/Al 2O 3 catalysts promoted by rare-earth oxides are able to achieve high HC, CO and NO conversions. The behaviour of the catalysts in the cold start period was determined by analysis of light-off temperatures and a comparison was made with those corresponding to some commercial samples and others reported in the literature. The catalysts prepared in this work showed lower light-off temperatures than those of commercial and reported Pt/Al 2O 3 catalysts but these temperatures were not so low as with PtRh/Al 2O 3. In all cases, the prepared catalysts resulted in a better resistance to accelerated ageing. Samples with ceria showed the best resistance to accelerated ageing.

Ambient temperature effect on urban CO air quality

Changes in the ambient temperature cause changes in vehicle emissions mainly during the cold-start period of operation. The influence that this effect has on the seasonal variation of urban CO concentrations is examined by means of a simple air quality model. For fixed meteorological conditions, the model predicts that the atmospheric CO concentrations at a center city measuring location will increase by 5–15% for a decrease in temperature from 75° to 25°F when none of the vehicles in that vicinity are in the cold-start mode and will increase by 55–75% when all of the nearby vehicles are in the cold-start mode. An inverse variation of CO concentration with change in temperature is derived from a statistical analysis of CO data reported both for midtown Manhattan (1975–1977) and for downtown Los Angeles (1970–1975). The magnitude of the derived variation is small for both cities and corresponds to the case where none of the vehicles in the vicinity of the measuring site are in the cold-start mode. It therefore follows that the variation of CO vehicle emissions with temperature does not have an important effect on CO air quality at these two urban centers. The highest CO concentrations are observed during the colder months in most American cities and the differences in meteorological conditions between winter and summer that might contribute to this are considered. Some significant factors are that, in the winter, multiday episodes of slowest dilution occur as well as nocturnal inversions of greater stability. From these considerations it is concluded that the meteorological factors play a significant role in the observation of high CO concentrations in urban areas during the colder months.