The fuel molar weight impact on filling, and indicator indices of a piston combustion engine

Аuthors

Matiukhin L. M.

Moscow Automobile and Road Construction State Technical University (MADI), MADI, 64, Leningradsky Prospect, Moscow, 125319, Russia

e-mail: panam1@mail.ru

Abstract

The problems arising while improvement of any type of the internal combustion engine (ICE), such as reciprocating, rotary-piston, gas turbine or jet engines, are common for all of them.

The notions of the volumetric efficiency (n_v) and residual gases (γ_r) traditionally used in the theory of piston internal-combustion engines do not allow characterize the air-fuel mixture composition, which defines the all power, economic and ecological indices of the engines. All the above-mentioned coefficients are applied only while the reciprocating ICE design. With this, the main indicator of pistons filling, namely volumetric efficiency, characterizes not so much the cylinders’ filling as its downgrade due to the presence of hydraulic resistances and incoming charge warming up. The essential drawback of all known equations for the volumetric efficiency determination is ignoring the impact of the fuel type, excess-air coefficient and recirculation’s degree on the cylinders filling. The general-technical concepts of (volume) fractions are far more informative. The aggregate of air-fuel mixture fractions determines its composition and thermodynamic characteristics values. The incoming charge (air) fraction allows unambiguous judgment on the degree of filling the whole cylinder volume, i.e. on the existing reserves of filling. Using the air or mixture volumetric fraction as the main filling indicator while piston ICE cycle computing allows accounting for the fuel molar weight and recirculation impact on the engine indices. As the result of the analysis, in order to account for the fuel impact on the filling the so-called “displacement coefficient” was proposed. Power and economic indices of the engine depend on this coefficient value. The value of this coefficient determines the degree of qualitative power regulation efficiency. Together with the recirculation degree, this coefficient determines the value of stoichiometric relationships and, thus, affects the indicator and effective indices of the engine.

As the sum of the fractions equals to the one, there is no necessity with the suggested approach in separate determining the fraction of the residue gases, since this fraction is equal to the difference between the one and the incoming charge fraction. The suggested approach is of prime importance while analyzing operating cycles of the engines operating on gaseous fuels, and on hydrogen in particular. As a result, the structure of the main calculation dependencies is simplified, and their analysis becomes more clearly evident and easy- to-understand. The possibility of the computing results visualization facilitates their analysis and is a great advantage of the suggested approach in terms of didactics.

Employing the ICE computation as a base of the air-fuel mixture fractions in modern applied programs might have led to the labor intensity reduction and execution time cutting due to the number of variables reduction.

Keywords:

piston internal combustion engine, gas exchange, filling, volumetric efficiency, volumetric fractions of air-fuel-residual mixture, molar weight, gaseous fuels, stoichiometric relationships, hydrogen

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