Michał Gęca

Indicated Mean Effective Pressure Oscillations in a Natural Gas Combustion Engine

Fluctuations in a combustion process of natural gas in the internal spark ignition engine have been investigated. We measured pressure of the cyclic combustion and expressed its cyclic oscillations in terms of indicated mean effective pressure per cycle. By applying the statistical and multifractal analysis to the corresponding time series we show the considerable changes in engine dynamics for a different equivalence ratio decreases from 0.781 to very lean conditions.

Transient combustion timing management in controlled auto-ignition engine based on ion current signal

This study investigates the effects of mixture stratification on ion current signal from combustion chamber of controlled auto-ignition (CAI) engine fueled with gasoline. The CAI combustion mode was achieved by application of exhaust gas retention obtained via negative valve overlap. Split direct fuel injection technique was applied to achieve different degrees of fuel stratification, maintaining constant global mixture composition. As expected, mixture distribution within combustion chamber had strong effect on levels of recorded ion current. The aim of the study was verification of possibilities of using ion current measurements for transient control of combustion timing. It was yielded by analysis of characteristic phases of heat release rate and ion current signal. Correlations of combustion timing derived from in-cylinder pressure analysis and ion-current proved applicability of this measurement technique for CAI combustion control.

Determination of common rail injector flow characteristics with the use of diesel and biodiesel fuels

One of the most important requirements in the design of diesel combustion systems is to reduce emissions of harmful chemical compounds contained in exhaust gases. Solution to this problem is sought by the use of advanced engine injection systems and accurate control of mixture formation inside a cylinder via split fuel injection. The differences in physical characteristics between traditional and alternative fuels can affect fuel metering, especially at short injection durations. Thus, the aim of the current study was to identify dynamic flow parameters of the Common Rail injector with the use of different fuels. The study involved Diesel available in retail and biodiesel fuel obtained by methyl esterification of fatty acids. Measurements were performed on a test stand designed for determination of injectors and injection pumps characteristics. Studies were carried out changing the following parameters: injection pressure in the range of 30-180 MPa, injection time in the range of 200-1600 microseconds. Each fuel was tested at temperature 40 and 60°C. The obtained test results showed that injection of different fuels provided variable amounts of fuel injected at short injection durations, which can affect mixture formation process as well as combustion. Effect of the dose of the injected fuel has a viscosity of used fuel.

Increase of high load limit in a gasoline HCCI engine

Engine operation in HCCI mode allows for improvement of thermal efficiency and substantial reduction NOX emission. The most production feasible solution for gasoline HCCI engine is application of exhaust gas trapping using a negative valve overlap. This technique increases thermal energy of a mixture, thus allowing for auto-ignition at moderate compression ratios. However, high exhaust gas re-circulation rate decreases volumetric efficiency. As a result, achievable engine loads are also reduced. Supercharging can be applied in order to improve volumetric efficiency and extend high load limit. However, increase of amount of intake air can lead to reduction of start of compression temperature via decrease of residuals in a mixture. In order achieve HCCI mode of combustion, temperature of start of compression must be kept within narrow limits. In this study experimental and modeling investigations were presented. Experiments were carried out using single cylinder research engine. The engine was equipped with fully variable valvetrain and direct gasoline injection. Application of mechanical boosting allowed for widening achievable load range in HCCI mode of operation. Numerical calculations allowed for determination of admissible valvetrain settings and intake pressure, which guarantee proper temperature of start of compression.