Evaluation of Various Dynamic Issues During Transient Operation of Turbocharged Diesel Engine with Special Reference to Friction Development

Abstract

The modeling of transient turbocharged diesel engine operation appeared in the early seventies and continues to be in the focal point of research, due to the importance of transient response in the everyday operating conditions of engines. The majority of research has focused so far on issues concerning thermodynamic modeling, as these directly affect heat release predictions and consequently performance and pollutants emissions. On the other hand, issues concerning the dynamics of transient operation are often disregarded or over-simplified, possibly for the sake of speeding up program execution time. In the present work, an experimentally validated transient diesel engine simulation code is used to study and evaluate the importance of such dynamic issues. First of all, the development of various forces (piston, connecting rod, crank and main crankshaft bearings) is computed and illustrated in order to evaluate the importance of abrupt load increases on the bearings durability. The usual approximation of the connecting rod being considered as equivalent to two masses (one reciprocating with the piston and the other rotating with the crank) is put into test. The same holds true for another usual assumption, i.e. the crankshaft being considered as sufficiently rigid. In this work, the engine crankshaft is analyzed in detail with the instantaneous torsional angle between engine and load taken into account. Thus, details are provided concerning the development of crankshaft torsional deformation during transients. The main part of the paper focuses on the development and contribution of various friction components during turbocharged diesel engine transients. This is accomplished via the use of a recently proposed detailed friction model. Mean fmep (friction mean effective pressure) modeling is found to considerably underestimate actual friction around firing TDC, leading to lower speed droops for abrupt load increases. The piston rings assembly contribution is dominant for the particular engine, due to its high number of piston rings and its relatively low crankshaft speed. The model can be used to investigate such interesting cases as the effect of engine oil temperature on engine transient response, or the variation of oil film thickness during a cycle or a transient event.

Instantaneous crankshaft torsional deformation during turbocharged diesel engine operation

“…The latter will be used in the next section for the computation of the engine-indicated torque. However, according to the previous research by the same group (Rakopoulos et al, 2007), inclusion of the connecting rod true motion only marginally affects the obtained results.…”

“…However, it induces errors in the slider-crank mechanism dynamics (of the order of a few percentage points) by miscalculating the actual rod's moment of inertia and the various forces of the kinematic mechanism. For a more accurate computation of engine (inertia) torque, the present research group has developed a detailed model of the connecting rod based on rigid body dynamics (Rakopoulos et al, 2007). Here, we analyse the complex, elliptical movement of the rod's Centre of Gravity (CG) that is produced by its reciprocating and rotating motion providing a 3 by 3 system of algebraic equations that can be solved for the unknown forces F thr , F 3 and F 4 ( Figure 1).…”

Exhaust emissions estimation during transient turbocharged diesel engine operation using a two-zone combustion model

“…where p g ( ) is the instantaneous cylinder pressure and R 1 ( ) = u pist /r , with u pist the instantaneous piston velocity. For the calculation of inertia force F Tin , a detailed model is applied treating the connecting rod as a rigid body experiencing reciprocating and rotating movement at the same time (Rakopoulos, Giakoumis and Dimaratos, 2007). Also, fr ( , ) stands for the friction torque during transient operation and is modelled as analysed in the previous sub-section.…”

“…During the last decades, diesel engine modelling has intensively supported the study of engine operation under transient conditions with simulations of various levels of complexity. Extensive studies have been conducted for a variety of purposes, such as investigation of the effect of various parameters on engine transient response (Watson and Janota, 1982;Winterbone, 1986;Benajes, Luján and Serrano, 2000;Rakopoulos et al, 2004a;Rakopoulos and Giakoumis, 2006b), ways of improving response (Watson, 1984;Rakopoulos and Giakoumis, 2006a), compressor surging (Rakopoulos, Michos and Giakoumis, 2005), second-law balance (Rakopoulos and Giakoumis, 2004) and issues concerning engine dynamics (Rakopoulos, Giakoumis and Dimaratos, 2007).…”

Study of crankshaft torsional deformation under steady-state and transient operation of turbocharged diesel engines

“…The elastic crankshaft rotary motion is excited by the gas and inertia torque fluctuation. The following two, non-linear differential equations apply [7,13,26]…”