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Technical Paper

Determination of the Gas-Pressure Torque of a Multicylinder Engine from Measurements of the Crankshaft's Speed Variation

The local variation of the crankshaft's speed in a multicylinder engine is determined by the resultant gas-pressure torque and the torsional deformation of the crankshaft. Under steady-state operation, the crankshaft's speed has a quasi-periodic variation and its harmonic components may be obtained by a Discrete Fourier Transform (DFT). Based on a lumped-mass model of the shafting, correlations are established between the harmonic components of the speed variation and the corresponding components of the engine torque. These correlations are used to calculate the gas-pressure torque or the indicated mean effective pressure (IMEP) from measurements of the crankshaft's speed.
Technical Paper

Diesel Engine Diagnosis Based on Analysis of the Crankshaft's Speed Variation

The variation of the crankshaft's speed is influenced by the action of the cylinders and shall reflect the contribution of each cylinder to the total engine output. At the same time, the speed variation is influenced by the torsional stiffness of the cranks, the mass moments of inertia of the reciprocating mechanisms and the average speed and load of the engine. As the result, the variation of angular motion of the crankshaft is complex, each particular influence changing its importance as speed and load are modified. The diagnostic method presented in the paper is based on the analysis of the amplitudes and phases of the lowest harmonic orders of the measured speed and is capable to determine the average Indicated Mean Effective Pressure (IMEP), to detect nonuniformities in cylinder operation and to identify the faulty cylinder(s).
Technical Paper

Estimation of Main Combustion Parameters from the Measured Instantaneous Crankshaft Speed

The increased interest for using alternative fuels in modern diesel engines requires better combustion control to achieve safe and efficient operation with fuels characterized by different physical and chemical properties. Knowing the ignition delay and the cylinder peak pressure will allow adapting the injection strategy, mainly injection timing to maintain good engine efficiency when operating with different alternative fuels. The use of the measured instantaneous crankshaft speed to estimate peak cylinder pressure and ignition delay is very attractive because speed is already a parameter in the ECU of the engine. Based on models using powertrain dynamics, the paper presents the development of several techniques using the measured speed to estimate the main combustion parameters for single cylinder and four cylinder diesel engines.
Technical Paper

Quantifying Relationships Between the Crankshaft's Speed Variation and the Gas Pressure Torque

The non-uniform character of the torque produced by a reciprocating I.C. engine is reflected in the cyclic variation of the crankshaft's speed. Because the crankshaft is an elastic structure, its response to the different harmonic components of the torque is different and changes with engine speed. The lowest harmonic components of the engine torque do not excite torsional vibrations and correlate fairly well with the corresponding harmonic orders of the crankshaft's speed. Based on a random vector model of the harmonic components of the gas-pressure torque, a statistical correlation is obtained between amplitudes and phases of the same harmonic component of the gas-pressure torque and of the crankshaft's speed. The lowest major harmonic order determines the average IMEP of the engine and the half-order detects if a cylinder is a lesser contributor to the total engine output and identifies the deficient cylinder.