Development of approaches to form algorithms to control processes in a closed fuel vapor recovery system of vehicles with hybrid powertrains

Introduction (problem statement and relevance). Besides the toxic substances generated during fuel combustion in an internal combustion engine (ICE), a vehicle generates a significant amount of hydrocarbons in the form of fuel vapors emerging as a result of evaporation from the fuel tank and fuel system components. At the moment, combined or hybrid powertrains are becoming more and more common and widespread, primarily in plug-in hybrid electric vehicles (PHEVs), series production of which has been organized by the majority of modern automobile manufacturers. A fundamental difference between a PHEV and a conventional hybrid vehicle is availability of an increased capacity battery that allows long-time pure electric driving with the ICE off. At the same time, no canister purging is performed. Therefore, research into vapor generation processes and finding solutions to minimize them are relevant.

The purpose of the study is to develop approaches to forming of an optimum strategy and algorithms of step-by-step determination of fuel tank isolation valve (FTIV) functioning with definition of the optimum beginning and number of steps of opening.

Methodology and research methods. The study used a combination of analytical methods of classical thermodynamics.

Scientific novelty and results. It has been found that transition from loading the canister with an open vapor space to evaporation in a constant-volume space allows significant reduction in the amount of hydrocarbons delivered to the canister. It is shown that to optimize the functioning process of the fuel vapor recovery system it is necessary to provide achievement of the maximum pressure of the mixture at the highest possible temperature. Upon that, the initial loading of the canister will be delayed, and the maximum amount of hydrocarbons will be accumulated in the tank in the gas or vapor phase.

Practical significance. The dependences obtained allow forming optimum algorithms to control the canister loading by varying the pressure release depth depending on fuel properties and vapor space volume in successive steps of canister loading and temperature intervals between them. It is shown that preventive release of pressure of the fuel-air mixture with its deaeration, resulting in a part of air mass being removed from the vapor space, allows considerable extension (by a quarter) of the functioning temperature range without opening the vapor space.

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