The soot emissions from diesel engines have serious health implications and have also been seen to influence the air quality and climate and, as such, must be reduced. To aid in the optimal operation of modern diesel engines, a mean value soot model (MVSM) was developed and validated for the rapid calculation of the engine soot emissions from diesel engines, operating under steady state and transient conditions. In addition, experimental investigations were carried out using exhaust stream and in-cylinder instrumentation to elucidate the influences of transient engine operation and fuel composition on the soot emissions.

The MVSM was developed through the reduction of an existing crank angle resolved soot model, based on the consideration of representative mixture states for combustion, soot formation, and soot oxidation. While the crank resolved model required the temporally resolved cylinder pressure, heat release rate, and fuel injection rate histories, the developed MVSM required only parameters available from the engine control unit. Because of this significant restriction in available information, the MVSM uses 16 model parameters to describe the combustion and soot formation and oxidation processes, which were determined for each engine and fuel combination using evolutionary algorithms. The parameterized MVSM was capable of calculating the engine out soot emissions in 10 ms per operating point, compared to 5 s required by the crank angle resolved model.

The MVSM was validated against steady-state exhaust stream soot measurements from two different engines operating with three different fuels, as well as for transient operation on one engine. It was found that the MVSM was capable of reproducing the qualitative and quantitative soot emission trends for the considered fuels and engines over a wide range of engine operating points. From the steady-state validation and sensitivity analyses, it was found that an accurate estimate of the EGR rate and intake charge temperature are required to ensure acceptable performance from the MVSM. Given that these inputs were available with sufficient temporal resolution, the MVSM was capable of reproducing the qualitative and in part quantitative soot emissions tendencies during tip-in (load changes) and acceleration (engine speed changes) transients. The MVSM had difficulty consistently reproducing the magnitude of the soot emissions "spike", but it was capable of reproducing a short term reduction observed immediately after the transient. The strong dependance of the calculated soot emission on the temperature was attributed to the use of a equivalence ratio - temperature map to describe the soot formation process. In general, the MVSM was found to consider the formation processes almost exclusively while changes in oxidation relevant parameters had a relatively small influence on the calculated soot emissions.

The MVSM has shown itself to be capable of predicting the soot emissions during steady state operation over a wide range of operating conditions on different engines, with different fuels. It does however require further development in order to more accurately calculate the soot emissions during transient engine operation. To this end, the insensitivity of the MVSM to oxidation parameters must be explored and remedied. Additionally, the influences of transient operation on the soot emissions could be further investigated and used for the further development of the MVSM with particular regard to transient operation.

In addition to serving as a basis for the validation of the MVSM, the steady state and transient measurements were used to gain insight as to the underlying mechanisms of soot formation and oxidation. To validate the use of in-cylinder pyrometry to describe soot emissions tendencies noted in the exhaust stream, the in-cylinder particle concentrations at the end of oxidation were compared with the exhaust stream soot measurements. The correlation coefficient between the two methods was found to range from R2 = 0:​42 to R2 = 0:​87, depending on the cylinder under consideration and the sensor being used. During steady state measurements with a reference fuel and a second fuel with a lower aromatic content and evaporation temperature, the soot emissions were seen to be lower with the second fuel. Through the use of in-cylinder pyrometry measurements, the lower engine out emissions were attributed to reduced in cylinder soot formation, caused by the lower aromatic content.

From the exhaust stream soot measurements during the tip-in and acceleration transients, an increase in the soot emissions compared to steady-state operation was seen for the tip-in transients, though the acceleration transients were not seen to have a considerable influence on the soot emissions. The increase in the soot emissions during the tip-in transients, particularly those of short duration at low engine speeds, was attributed a short-term oxygen deficit as quantified by the global relative oxygen-fuel ratio. This hypothesis was validated by the in-cylinder measurements which indicated that the soot emission increase corresponds with an unchanged soot formation process (compared to steady-state operation) coupled with a slow and incomplete oxidation.