Browse Topic: Evaporative emissions control systems (EVAP)
Due to the vibration of the vehicle, the performance of the vehicle carbon canisters will be changed, which will affect its control effect on the fuel evaporation emission. In this study, a vibration test platform capable of simulating vehicle vibration characteristics was used to simulate the possible vibration effects of the vehicle carbon canisters, and to analyze the absorption and desorption performance of the carbon canisters before and after long-term operation and its influence on vehicle evaporation emissions. The results show that the carbon canisters will precipitate the carbon powder after the continuous action of the forward and backward vibration of the vehicle. As a result, the ultimate adsorption and desorption amount of fuel vapor decreased, and the adsorption amount decreased more obviously. In the 48-hour Diurnal Breathing Loss (DBL) test, fuel vapor diffusion is more difficult due to the increased flow resistance of the carbon canisters after vibration, and fuel loss is reduced under unsaturated conditions, resulting in lower actual evaporative emissions. In evaporative emission control, it is necessary to adjust the control strategy reasonably according to the change of the working state of the carbon canisters.
Under contract to the EPA, Eastern Research Group analyzed light-duty vehicle OBD monitor readiness and diagnostic trouble codes (DTCs) using inspection and maintenance (I/M) data from four states. Results from roadside pullover emissions and OBD tests were also compared with same-vehicle I/M OBD results from one of the states. Analysis focused on the evaporative emissions control (evap) system, the catalytic converter (catalyst), the exhaust gas recirculation (EGR) system and the oxygen sensor and oxygen sensor heater (O2 system). Evap and catalyst monitors had similar overall readiness rates (90% to 95%), while the EGR and O2 systems had higher readiness rates (95% to 98%). Approximately 0.7% to 2.5% of inspection cycles with a “ready” evap monitor had at least one stored evap DTC, but DTC rates were under 1% for the catalyst and EGR systems, and under 1.1% for the O2 system, in the states with enforced OBD programs. Monitor readiness decreased, and DTC rates increased, as vehicles aged. DTCs were typically limited to a small subset of all possible DTCs for any particular system. For the on-road versus I/M analysis, lower overall readiness rates and higher overall DTC rates occurred during the roadside test than during the I/M test, and the prevalence of roadside DTCs was shown to decrease around the time of the vehicle’s I/M test, possibly indicating some positive I/M influence of reducing on-road DTCs. Roadside Acceleration Simulation Mode (ASM) fail rates also decreased around the time of the I/M test, suggesting a positive influence of I/M programs on reducing vehicle emissions.
In gasoline Powertrain systems, the evaporative emission control (EVAP) system canister purge valve (CPV) can be actuated by pulse-width modulated (PWM) signals. The CPV is an electronically actuated solenoid. The PWM controlled CPV, when actuated, creates pressure pulsations in the system. This pulsation is sent back to the rest of the EVAP system. Given the right conditions, the fill limit vent valve (FLVV) inside the fuel tank can be excited. The FLVV internal components can be excited and produce noise. This noise can be objectionable to the occupants. Additional components within the EVAP system may also be excited in a similar way. This paper presents a bench test method using parts from vehicle’s EVAP system and other key fuel system components. The test method achieves the following objectives: first, re-create the conditions that result in excitation; second, establish a controlled environment that provides insight into the noise phenomenon; and finally, set the ground work for further studies which may lead to further noise mitigation methods. The key system parameters controlled in this method are: frequency and duty cycle of the PWM signal, liquid level inside the fuel tank and tank grade/orientation. The output data includes: EVAP system purge flow rate, pressure signal inside the EVAP system (one near the CPV and one near the FLVV) and acceleration in Z (vertical) direction on the top tank surface near the FLVV mounting location.
In order to meet more stringent evaporative emissions requirements, multiple advancements in vehicle fuel system and carbon canister technologies have been made. Regardless of technological advancements, the vapor pressure of the fuel remains a vital property in controlling evaporative emissions. A series of tests were performed to explore the effects of vapor pressure on multiday diurnal evaporative emissions for 9 and 10 psi Reid Vapor Pressure (RVP) 10% ethanol (E10) gasoline-blend fuels, followed by tests with 7 psi RVP E10 gasoline on a subset of the same vehicles. A test procedure was developed to monitor evaporative emissions, canister loading profiles and breakthrough emissions for each of the fuels. A total of five vehicles were tested on all 3 fuels, blended to represent 7, 9, and 10 psi at sea level. Tests were run over 14 days using the United States (U.S.) Federal Diurnal Cycle (72°F to 96°F) in a Sealed Housing for Evaporative Determination (SHED) at a test facility in Colorado. Two of the five vehicles had evaporative emissions systems that met the California Air Resources Board (CARB) requirements for a Partial Zero Emission Vehicle (PZEV), while the other three vehicles were certified to U.S. Tier 2 evaporative emissions standards. The data collected throughout the testing provide a correlation between the hydrocarbon slip from the vehicle canister and the fuel vapor pressure. The data indicate that achieving lower evaporative emissions can be accomplished through the use of decreased vapor pressure fuels.
This SAE Recommended Practice applies to nomenclature of emissions and emissions reduction apparatus as applied to various engines and vehicles. Modifying adjectives are omitted in some cases for the sake of simplicity. However, it is considered good practice to use such adjectives when they add to clarity and understanding.
Exhaust and evaporative emissions systems have been developed to match the characteristics and usage of the Toyota THS II plug-in hybrid electric vehicle (PHEV). Based on the commercially available Prius, the Toyota PHEV features an additional external charging function, which allows it to be driven as an electric vehicle (EV) in urban areas, and as an hybrid electric vehicle (HEV) in high-speed/high-load and long-distance driving situations. To reduce exhaust emissions, the conventional catalyst warm up control has been enhanced to achieve emissions performance that satisfies California's Super Ultra Low Emissions Vehicle (SULEV) standards in every state of battery charge. In addition, a heat insulating fuel vapor containment system (FVS) has been developed using a plastic fuel tank based on the assumption that such a system can reduce the diffusion of vapor inside the fuel tank and the release of fuel vapor in to the atmosphere to the maximum possible extent. As a result, these measures have enabled the mass-production of the world's first PHEV that satisfies California's SULEV and zero evaporative emissions standards.
In order to correspond to the exhaust emissions regulations that become severe every year, more advanced engine control becomes necessary. Engine engineers are concerned about the Hydrocarbons (HCs) that flow through the air-intake ports and that are difficult to precisely control. The main sources of the HCs are, the canister purge, PCV, back-flow gas through the intake valves, and Air / Fuel ratio (A/F) may be aggravated when they flow into the combustion chambers. The influences HCs give on the A/F may also grow even greater, which is due to the increasingly stringent EVAP emission regulations, by more effective ventilation in the crankcase, and also by the growth of the VVT-operated angle and timing, respectively. In order to control the A/F more correctly, it is important to estimate the amount of HCs that are difficult to manage, and seek for suitable controls over fuel injection and so on. Therefore, the authors have developed a HC concentration measuring technology for the air-intake system using FID of which gas sampling performance has been remarkably improved. The characteristics of the system are as follows; 1. Applicable to each point of the intake system 2. Applicable to all engine operating conditions including the transition stage 3. Small influences on the A/F control by gas sampling 4. High accuracy; 1%F.S. This report presents the results gained from the several tests carried out on EVAP purging, PCV gas supplying, and VVT system operation, as well as on the process of measuring technology development.
This paper discusses an approach to detecting small leaks in an automobile's evaporative emissions systems that is a technique based upon ideal gas laws. It does this by monitoring pressure in the system while the vehicle's engine is off. This low cost solution can be easily implemented on General Motors vehicles using existing components. The topics covered in this paper include details on the background of the problem and the technique, the underlying thermodynamics of the technique, a description of the algorithm, testing and data collection considerations.
Recently, the California Air Resources Board (CARB) has proposed a new set of evaporative emissions and “Useful Life” standards, called LEVII EVAP regulations, which are more stringent than those of the enhanced EVAP emissions regulations. If the new regulations are enforced, it will become increasingly important for the carbon canister to reduce Diurnal Breathing Loss (DBL) and to prevent deterioration of the canister. Therefore, careful studies have been made on the techniques to meet these regulations by clarifying the working capacity deterioration mechanism and the phenomenon of DBL in a carbon canister. It has been found that the deterioration of working capacity would occur if high boiling hydrocarbons, which are difficult to purge, fill up the micropores of the activated carbon, and Useful Life could be estimated more accurately according to the saturated adsorption mass of the activated carbon and the canister purge volume. As a result, it is presumed that a more adaptable, longer Useful Life can be realized by providing a sufficient purge. It has been also found that the butane diffusion in a carbon canister during vehicle parking which is loaded to the canister during the DBL test, is the main cause of evaporative emissions from the canister. To prevent such diffusion, it is effective to divide the carbon bed into separated segments and insert some “labyrinth” between such carbon beds. Compared with the conventional canister, the improved canister was able to reduce DBL by half._Furthermore it became clear that DBL is reduced to approximately 1/3 when the gasoline fuel vapor is loaded to the canister instead of butane, which is the main cause of DBL. It was also concluded that the evaluation method should be reconsidered to account for real world conditions.
This recommended practice applies to nomenclature of emissions and emissions reduction apparatus as applied to various engines and vehicles. Modifying adjectives are omitted in some cases for the sake of simplicity. However, it is considered good practice to use such adjectives when they add to clarity and understanding.
This recommended practice applies to nomenclature of emissions and emissions reduction apparatus as applied to various engines and vehicles. Modifying adjectives are omitted in some cases for the sake of simplicity. However, it is considered good practice to use such adjectives when they add to clarity and understanding.
The effect of fuel composition on automotive evaporative emissions has been studied using five cars, not equipped with evaporative emission controls, and a total of 31 fuels. The amount of evaporative emissions increased with increasing fuel volatility. Also, the evaporative emission photochemical reactivity per gram increased with increasing C4 and C5 olefins in the fuel and decreased with increasing C4 and C5 paraffins. For an assessment of the smog potential of evaporative emissions, the amount and reactivity per gram should not be considered independently, since they both are simultaneously dependent on fuel composition. The product of amount and reactivity per gram (the Evaporative Reactive Index) is a good measure of the contribution of evaporative emissions to photochemical air pollution. An empirical equation for predicting the Evaporative Reactive Index from fuel properties has been derived. First, the two-part equation predicts the emission amount from the percent fuel evaporated in an ASTM distillation at 160 F and the fuel’s Reid vapor pressure. Second, the reactivity per gram of the evaporative emissions can be determined from the percent C4 and C5 olefins and the percent C4 and C5 paraffins in the fuel. Utilization of the Evaporative Reactive Index (ERI) may be illustrated by the following examples. Removal of 65% of the butane from the typical Los Angeles gasoline would reduce the fuel evaporated at 160 F from 29 - 23% and lower Reid vapor pressure from 9.5 - 7 psi. The ERI equation would predict a decrease in evaporative emission amount from 110 - 68 gm/day and an increase in reactivity per gram (based on the NO2 formation rate scale) from 0.049 – 0.055. The ERI (NO2) would decrease from 5.4 - 3.7 (31%). On the other hand, replacement of the C4 and C5 olefins in the same fuel with C4 and C5 paraffins would not affect the percent evaporated at 160 F, Reid vapor pressure, or emission amount; but the equation would predict a decrease in reactivity per gram (NO2) from 0.049 - 0.028 and a decrease in the ERI (NO2) from 5.4 - 3.1 (43%).
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