A complex multidisciplinary optimization task – Selection of the Firing Order in FEV Virtual Engine

9. May 2016 | Software & Testing Solutions

The continuously increasing mechanical and thermal load of modern engines calls for design optimizations over a wide range of aspects. The development process of many engine components supported by various computer simulations is currently advanced and well-defined, leading to the creation of highly optimized products. However, the optimization of design variables such as the firing order, which influences engine operation with respect to several disciplines, is still challenging. To bridge this gap, the Firing Order Investigation Tool under implementation for the commercial simulation software FEV Virtual Engine can play a central role in the realization of this comprehensive task.

Firing order optimization problem

The selection of a firing order for engines with only a few cylinders is a rather simple task, as the alternatives are limited. However, the number of possible firing sequences rises sharply with the number of cylinders, and in engines such as the V16 or V20 it reaches hundreds or thousands of possibilities.

The firing order influences crank train vibration (torsional or axial), overall vibration of the engine structure including NVH behavior, performance of hydrodynamic bearings, and gas dynamics at the intake and exhaust ducts, thus making selection of the firing order a comprehensive multidisciplinary optimization problem.


New Virtual Engine tool supporting firing order selection process

The key functionality of the FEV Virtual Engine’s Firing Order Investigation Tool is the so-called crankshaft-based firing order definition procedure, which automatically generates a list of all alternative firing orders for a defined crankshaft design,preserving the desired engine balancing concept and significantly reducing the number of firing order alternatives to only the technically feasible ones.

By using the fast solver of FEV Virtual Engine’s Crank Concept Analysis (CCA) tool, which couples torsional vibration simulation in the frequency domain with quasi-static bending analysis, the full factorial investigation of the firing order influence can be executed very efficiently.

The Firing Order Investigation Tool is additionally equipped with a unique evaluator, where not only CCA results but also results derived from external software and detailed design simulations can be considered.

Firing order

Number of firing orders for selected engine configurations with typical crankshaft layouts

Virtual Engine_Diagramm

Exemplary torsional vibratory stress amplitudes of V16 engine for alternative firing orders realized by one crankshaft design