Search Results

New regulations require small gasoline engine evaporative diurnal emission control. In the past, it was not possible to design a proper evaporative emission control system (it was mostly trial and error design). In this study, a mathematical model was developed for estimating activated carbon canister size and nomographs were developed for estimating canister purge air requirements and diurnal bleed emissions. The model and the nomographs can be used to design an evaporative emission control system for any SI engine fuel system.

Diurnal evaporative emissions from a vehicle's gasoline (petrol) tank are due to the increase in gasoline vapor pressure with ambient temperature over the course of a 24-hour period. Graphical illustrations are used to explain both the mechanism of these emissions and various control methods. The diurnal emissions can be controlled either by using either an activated carbon canister or a sealed/pressurized fuel tank. Mathematical models were developed for estimating tank vapor generation and activated carbon canister volume for storing the tank vapor. Nomographs were developed for estimating the canister purge air requirements and canister bleed emissions. The models and the nomographs can be used for designing an evaporative emission control system for a given vehicle fuel system. Another mathematical model was developed for estimating the sealed/pressurized fuel tank pressure as a function of fuel RVP (Reid Vapor Pressure) and temperature.

Mathematical models were developed for estimating refueling vapor generation as a function of tank fuel and dispensed fuel Reid vapor pressures and temperatures, and fill type (bottom fill vs. top fill). Since refueling vapor generation is a strong function of fill type (bottom fill vs. top fill), simple illustrative diagrams are presented to explain the mechanism of higher vapor generation from bottom fill type fuel tanks. The models are useful for estimating refueling vapor generation in any real world ambient conditions and with any fuel. The models have been verified with published experimental data.

Hydrocarbon permeation is one of the remaining main sources of vehicle evaporative hydrocarbon emission. However, very little information exists on the role of fuel properties on permeation losses. Therefore, experimental and modeling studies were conducted to determine the relationships between hydrocarbon permeation through HDPE (high density polyethylene) and fuel properties. Half-gallon HDPE bottles without EVOH were used in this study, because they were easily available and because steady state permeation can be measured in a matter of few days instead of several months in the case of HDPE/EVOH bottles. A permeation equation was developed using both theory and experimental data, which shows that permeation increases exponentially with fuel aromatic content, increases linearly with fuel RVP, and increases exponentially with temperature. The equation is useful for predicting how fuel and ambient temperature affect hydrocarbon permeation through vehicle fuel system.

Commingling of fuels containing various concentrations of ethanol can occur in a vehicle fuel tank. It was not possible to estimate the RVPs of commingled ethanol containing fuels because they form complex non-ideal solutions. A nomograph and an equation were developed using the theory and experimental data for estimating the RVP of a commingled ethanol fuel blend from the RVPs of two base fuels containing any amounts of ethanol. The model is also useful for general purpose estimation of vapor pressures of ethanol/gasoline blends such as seasonal blending of E85 fuels with the right vapor pressure gasoline and the right amount of ethanol to meet the seasonal fuel vapor pressure requirement.