The Effect of Various Dynamic, Thermodynamic and Design Parameters on the Performance of a Turbocharged Diesel Engine Operating under Transient Load Conditions

Abstract

Thermodynamic, dynamic and design parameters have a significant and often conflicting impact on the transient response of a compression ignition engine. Knowing the contribution of each parameter on transient operation could direct the designer to the appropriate measures for better engine performance. To this aim an explicit simulation program developed is used to study the performance of a turbocharged diesel engine operating under transient load conditions. The simulation developed, based on the filling and emptying approach, provides various innovations as follows: Detailed analysis of thermodynamic and dynamic differential equations, on a degree crank angle basis, accounting for the continuously changing nature of transient operation, analysis of transient mechanical friction, and also a detailed mathematical simulation of the fuel pump. Each equation in the model is solved separately for every cylinder of the 6-cylinder diesel engine considered. The model is validated against experimental data for various load changes.The effect of several dynamic, thermodynamic and design parameters is studied, i.e. load schedule (type, and duration of load applied), turbocharger mass moment of inertia, exhaust manifold volume and configuration, cylinder wall temperature, aftercooler effectiveness as well as an interesting case of a malfunctioning fuel pump.Explicit diagrams are given to show how, after an increase in load, each parameter examined affects the engine speed response, as well as other properties of the engine and turbocharger such as fuel pump rack position, boost pressure and turbocharger speed.It is shown that certain parameters, such as the type of connected loading, the turbocharger inertia, a damaged fuel pump and the exhaust manifold volume, can have a significant effect on the engine and turbocharger transient performance. However others, such as the cylinder wall temperature, the aftercooler effectiveness and the exhaust manifold configuration have a less important effect as regards transient response and final equilibrium conditions.

Review of Thermodynamic Diesel Engine Simulations under Transient Operating Conditions

“…At a particular step in the cycle simulation, the tables or polynomials are interpolated in a two dimensional fashion to calculate two unknown map variables from two known variables. Rakopoulos and Giakoumis [40] reported that no difference in the predictions from a single-zone model was observed, if this computational step was less than 20 o CA.…”

“…With the notable exceptions from only five research groups [29,30,[39][40][41]44,45,69,88,146], friction modeling in transient simulation codes has always, in the past, been used in the form of 'mean fmep' relations, remaining constant for every degree crank angle in each cycle in the model simulation. This may be attributed to the fact that friction does not affect the heat release rate (and thus the interior engine 'indicating' properties and exhaust emissions) but only the crankshaft energy balance; the latter one being, nonetheless, essential for correct transient predictions.…”

“…To this aim, the model is a true multi-cylinder one, solving separately and sequentially the algebraic and differential equations for each cylinder; friction is modelled with detailed per degree equations, whereas a fuel injection sub-model is incorporated in order to consider the transient fuel pump operation. The model has been used for an extensive parametric study [40] and sensitivity analysis [41,42], covering, among many other things, various governor configurations [36], while it was also extended to second-law analysis [43][44][45][46] and investigation of compressor surging [47] (the latter on a quasi-linear basis).…”

“…This approach was adopted, for example, by Rakopoulos and Giakoumis [40] during transient calculations, using an SMD correlation proposed by Hiroyasu et al [139], accounting for variations in fueling, and compression and injection pressures.…”

“…Rakopoulos and Giakoumis [39,40] incorporated the Rezeka-Henein model in a transient simulation code, and compared the results with the usual fmep approach. They showed that mean fmep modeling could underestimate engine speed response by up to 12% for a turbocharged, heavy-duty diesel engine.…”