Search Results

Two-stroke S.I. engine survival is submitted to direct fuel injection and charge stratification. An exhaustive activity concerning a 50 cm3 two-stroke S.I. engine with liquid direct injection and charge stratification has given really satisfactory results as regards engine aptitude to operate unthrottled at every speed and load. However, unthrottled operation does not necessarily lead to the best overall result. By CFD investigation and experimental tests, this paper proves that some throttling reduces HC and NOx emissions as well as pumping loss and increases exhaust gas temperature at light loads, with evident advantage for catalytic converter efficiency.

A low-pressure hydrogen direct-injection solution is presented that allows some typical benefits of direct injection, such as high specific power and backfire prevention, plus low residual storage pressure, that improves vehicle range and is a typical advantage of external mixture formation. Since the injection must end early enough to allow good charge homogeneity and, in any case, before in-cylinder pressure rise constraints hydrogen admission, especially at heavy loads hydrogen flow to the cylinder is higher than present electro-injectors allow. The injection is realised in two steps: hydrogen flow rate is simply controlled by a conventional CNG electro-injector that feeds a small intermediate chamber. From this chamber hydrogen next enters the cylinder in a short crank angle period by means of a mechanically-actuated valve that opens at the intake valve closure to avoid backfire.

This paper concerns a study of an innovative concept to control HCCI combustion in diesel-fueled engines. The concept consists in forming a pre-compressed homogeneous charge outside the cylinder and in gradually admitting it into the cylinder during the combustion process. This new combustion concept has been called Homogeneous Charge Progressive Combustion (HCPC). CFD analysis was conducted to understand the feasibility of the HCPC concept and to identify the parameters that control and influence this novel HCCI combustion. A CFD code with detailed kinetic chemistry (AVL FIRE) was used in the study. Results in terms of pressure, heat release rate, temperature, and emissions production are presented that demonstrate the validity of the HCPC combustion concept.

This paper concerns an innovative concept to control HCCI combustion in diesel-fuelled engines. It was named Homogenous Charge Progressive Combustion (HCPC) and operates on the split-cycle principle. In previous papers the feasibility of this combustion concept was shown for light-duty diesel engines. This paper illustrates a CFD study concerning a heavy-duty version of the HCPC engine. The engine displaces 13 liters and develops 700 kW indicated power at 2200 rpm with 49% maximum indicated efficiency and clean combustion.

High-pressure liquid fuel injection is a suitable means to get either stratified charge or homogeneous charge for two-stroke engines. This paper shows the development of this solution for a small 50 cm3 engine for light motorcycles. By means of computational fluid dynamics, a combustion chamber suitable for proper fuel distribution in every engine operating condition has been designed. It has been realized, and experimental results confirm its fairly satisfactory behaviour, with good fuel economy, low exhaust emissions and small cycle-to-cycle variation even at light loads. Recent CFD studies indicate how to improve engine geometry to achieve a better stratification stability at partial loads independently on engine speed.

A study was performed that takes into account both turbulence and chemical kinetic effects in the numerical simulation of diesel engine combustion in order to better understand the importance of their respective roles at changing operating conditions. An approach was developed which combines the simplicity and low computational and storage requests of the laminar-and-turbulent characteristic-time model with a detailed combustion chemistry model based on well-known simplified mechanisms. Assuming appropriate simplifications such as steady state or equilibrium for most of the radicals and intermediate species, the kinetics of hydrocarbons can be described by means of three overall steps. This approach was integrated in the KIVA-II code. The concept was validated and applied to a single-cylinder, heavy-duty engine. The simulation covers a wide range of operating conditions.