The accumulation of particulate matter in lubricant oil can become an important issue in Diesel engines where large amounts of Exhaust Gas Recirculation (EGR) are used at medium to high load operating conditions. Indeed, the transport and subsequent accumulation of particulate matter in the engine oil can negatively impact the oil lubricant properties which is critical to ensure mechanical durability and limit the vehicle Total Cost of Ownership (TCO) by reducing the servicing intervals. The objective of this investigation was to gain an improved understanding of the underlying mechanisms that are responsible for the accumulation of particulate matter in the lubricating oil, and ultimately provide design guidelines to help limit this phenomenon.The present study presents the development and validation of experimental and numerical tools used to investigate this phenomenon. Several advanced diagnostic techniques were developed and applied on an optically-accessible single cylinder Diesel engine to detect the presence of particulates and quantify their concentration in two particular zones: (1) in the upper part of the cylinder liner where particulate matter is believed to be absorbed into the oil film and (2) in the engine blow-by gases where particulates can be transported via the piston ring-pack to the oil sump reservoir. The accumulation of soot particulates on the surface of the upper part of the cylinder liner was characterized using a modified Laser Extinction Method (LEM), while the concentration of particulates in the engine blow-by gases was measured using a DMS500 soot sensor. In parallel to the experimental study, 3D numerical computations were performed and provided additional information to the experimental results. In the present paper, the various experimental and numerical methods are presented and first validation results are discussed.

The last generation of turbocharged HSDI engines with high pressure injection systems has greatly contributed to meet the current demanding automotive emission standards. The very stringent EURO 4 emission regulation requires new efforts in engine research in order to further reduce emissions by 2005. Optimizing the shape of the combustion chamber and its geometrical details to improve the combustion process is a fundamental issue to achieve this goal. Such an optimization requires a better understanding of the combustion phenomena. CFD calculations can contribute to provide this knowledge. The present paper describes a recent work on Direct Injection Diesel engine combustion, with test-bench results and CFD calculations. The influence of valve pockets on the combustion process was investigated. Two versions of a 1.9 liter, 4 cylinder, 16 valve engine were tested on test-bench. One version showed higher soot emissions and less torque output than the other one. These versions had the same piston cavity but they were different in their valve inclination and their valve pockets configuration. The latter item was then investigated by CFD calculations using the KIVA-2-Renault code. This study demonstrated that deep valve pockets at the top of the piston induced more combustion in the squish area at the beginning of the expansion phase. The intersection between the spray cone and the top of the piston is indeed increased by the valve pockets. A more important part of the fuel is therefore injected directly into the squish area while the piston is still close to the cylinder head. The combustion in the squish area is subsequently confined in a reduced space and oxygen in this area is rapidly consumed, which induces higher soot emissions, a less dynamic combustion, and hence a lower IMEP. As a conclusion, these results show that CFD is an efficient tool for combustion chamber development and that the effect of the valve pockets at the top of the piston has to be further investigated.

This experimental work is linked to the recent development of Gasoline Direct Injection engines and is dedicated to the study of the airflow entrained by the hollow cone spray issued from an injector for Gasoline Direct Injection engines. This spray is a dense unstationary two-phase flow that interacts with the surrounding air. The mechanism of air entrainment, due to the momentum exchange between the spray drops and the gaseous phase is an important phenomenon responsible for droplets vaporisation and mixture formation. The latter are directly linked to the reduction of fuel consumption and pollutant emissions. By application of the PIV technique, measurements of air velocity near the spray edge have been performed and used to compute the mixing rate q in the spray, by mass conservation through a cylindrical control surface (q is defined as the ratio between the mass flow rate of entrained air and the liquid mass flow rate injected). The influence of two parameters on q is studied. The first one is the injection pressure (P i ) effect, P i varying from 30 to 90 bars at ambient pressure. The second one is the effect of the chamber back pressure (P c ) Three values of P c are investigated: 1, 5 and 8 bars for P i = 80 bars. Thanks to these results, air entrainment mechanisms in Gasoline Direct Injection spray have been discussed.

The simultaneous use of experimental and computational techniques allows us to achieve both a good understanding of the physical phenomena as well as quicker, safer and cheaper engine developments.