Search Results

New devices and control techniques have been adopted to take advantage of variable valve timing properties to improve engine performance or load control. This paper presents a study focused on engine load control strategies associated with early intake valve closing or late intake valve closing. It can be shown that these load control modes can improve the indicated thermal efficiency of the engine as compared with the conventional throttle control. These strategies are sometime called Miller cycle or Atkinson cycle, since the real compression ratio becomes smaller than the expansion ratio. A thermodynamic spark-ignition engine simulation model was employed. The advantage of a simulation model is to conduct parametric studies without the need of complex experimental apparatus. In this way, a deep understanding of the physical phenomena can be achieved and the sole effect of the desired parameter can be shown.

The controlled emissions limits defined to passenger cars are becoming very stringent. Therefore, the first minutes of the emissions test cycles gained importance. This work deals with a strategy to reduce the emissions of NMHC, CO and NOx in the cold phase of the test cycle, while the engine and catalyst are cold. Leaving the engine, the exhaust gases pass through a three- way catalyst to reduce controlled pollutant gases, but the catalyst is effective only above 300°C (the so-called light-off temperature). When the catalyst is not hot enough, the gases pass through the catalyst without any beneficial effect. In modern engines, most of the NMHC emissions occur in the cold phase; then, reducing this pollutant in the cold phase is the main objective of the adopted strategy. Besides, significant amounts of CO and NOx are formed during this phase and this must also be considered.

Engine efficiency is directly related with CO2 emissions (GHG) and is increasing nowadays. This growing concern with environment and efficient use of fuels induces the automotive industry to seek the increase the efficiency of all engine systems. Recently, Brazilian Government instituted new Automotive rules (the so-called Inovar Auto), which will also demand increased engine efficiency. Valve timing system is directly linked to all principal performance parameters, like power, torque and fuel consumption and its study can bring benefits to overall engine performance. The use of a thermodynamic simulation model enables exploratory studies to be conducted with low cost and time, with the identification of interesting valve timing strategies. This can direct efforts and reduce experimental work needs and costs. This work presents the study of the effects of some valve timing parameters on engine performance, seeking the best timings for full load engine operation conditions.

This paper describes the development of a computational simulation model for internal combustion engines, with spark ignition, powered by ethanol fuel which include the combustion with finite duration, the instantaneous heat transfer and the intake and exhaust processes. The simulation model calculates the thermodynamic properties of each element involved in the process at every discretized instant of the motor cycle using as input the data related to the engine and to its desired operating regime. The simulation model has as a result the temperature and the instantaneous pressure profiles inside of the combustion chamber as a function of the crankshaft angle in the range of one cycle. Besides that, the algorithm includes a variation range of certain parameters of the engine project to evaluate the influence of each one of these parameters in its performance.

The optimization of valve train actuation for internal combustion engines through the fixed geometry camshaft is a compromise between the required torque, the fuel consumption, idle characteristics and exhaust emissions. Some automobile manufacturers, however, have already incorporated in some models the variable valve actuation; in these systems, the duration of intake process, valve overlapping or both can be modified by the engine operation condition. Although experimental tests are the decisive ones, their costs can be minimized if it is possible to adopt some mathematical modeling of the engine physical phenomena in order to obtain qualitative tendencies. The analysis of the engine performance modifications associated with a variable camshaft actuation can be obtained - at least as a first approximation - through thermodynamic simulation models. Then the number of necessary experimental work can be reduced.

This work is based upon a simulation model for spark-ignition engines that considers the instantaneous heat transfer, the combustion process occurring at a finite rate as well as intake and exhaust processes. The model calculates the thermodynamic properties - including exergy - of each gas mixture composition of the working fluid. Besides the common features of thermodynamic simulation models, the determination of instantaneous irreversibilities, exergetic efficiencies of each process and an overall cycle exergetic analysis are also included. Based upon the simulation model, first and second law analysis are applied to a parametric study with emphasis in the combustion process and the valve timing effects. Exergy destructions taking place during the combustion of an ethanol fueled engine and a gasoline version of the same engine are compared.