Jacek Hunicz

Investigation of combustion in a gasoline engine using spectrophotometric methods

Spectrophotometric methods provide many new possibilities of investigation of combustion process in the automotive engine with spark ignition. Emission spectrum of the flames from the combustion chamber provides valuable information, which is difficult or even not accessible with the aid of other measurement methods. Spectral analysis allows to evaluate concentration of active compounds present in flames, which do not constitute final products of combustion. Concentration of radicals depends on some combustion parameters such as air-fuel ratio. The paper describes an engine test stand equipped with fiber-optic measurement system. The measurement system consists of an optical sensor mounted in the engine head, fiber-optic bundle for signal transmission, grating monochromator and photodetector. Voltage signal from the photodetector is recorded by the PC- based data acquisition system. The main aim of research was to verify usability of the designed fiber-optic measurement system in combustion diagnosis and to develop a method of evaluation of the air-fuel ratio on the base of simplified spectral analysis of the emission during combustion process in an automotive gasoline engine.

An experimental study into the chemical effects of direct gasoline injection into retained residuals in a homogeneous charge compression ignition engine

Fuel injection into retained residuals and the resulting exhaust-fuel reactions appear to be an effective method for enhancing mixture reactivity in residual effected homogeneous charge compression ignition engines. Varying the extent of reactions preceding the main combustion event enables the control of auto-ignition timing and heat release. Although fuel injection during the negative valve overlap period is widely utilised, there is still insufficient amount of data on its chemical effects. This study experimentally explores the species formation as a result of negative valve overlap exhaust-fuel reactions. To collect experimental data, a single-cylinder engine with negative valve overlap and direct gasoline injection was utilised. Valving strategy of the engine was strategically set to achieve a high rate of backflows at the end of the intake process. Negative valve overlap gas, diluted by intake air, was sampled from the intake runner and passed to a Fourier transform infrared analytical system. A dedicated procedure was applied to compute degrees of fuel conversion into species from the diluted samples. The experiments were designed to acquire comprehensive data on the effects of different fuel injection timings on species formation during negative valve overlap. The results showed that exhaust-fuel reactions could produce high quantities of methane and light unsaturated hydrocarbons. At early negative valve overlap fuel injection, up to 25% of fuel was converted into species, whereas chemical changes were negligible for late fuel injection. Additionally, the effects of excess air and amounts of fuel injected during negative valve overlap were investigated.

Effects of Direct Fuel Injection Strategies on Cycle-by-Cycle Variability in a Gasoline Homogeneous Charge Compression Ignition Engine: Sample Entropy Analysis

In this study we summarize and analyze experimental observations of cyclic variability in homogeneous charge compression ignition (HCCI) combustion in a single-cylinder gasoline engine. The engine was configured with negative valve overlap (NVO) to trap residual gases from prior cycles and thus enable auto-ignition in successive cycles. Correlations were developed between different fuel injection strategies and cycle average combustion and work output profiles. Hypothesized physical mechanisms based on these correlations were then compared with trends in cycle-by-cycle predictability as revealed by sample entropy. The results of these comparisons help to clarify how fuel injection strategy can interact with prior cycle effects to affect combustion stability and so contribute to design control methods for HCCI engines.

Diagnostics of abnormal combustion in a SI automotive engine using in-cylinder optical combustion sensor

The paper presents development of a research project oriented towards application of optical sensors and optical wave-guides for the investigation and diagnostics of the combustion process in the internal-combustion automotive engine. Applied measurement method assumes usage of photometric techniques, and in particular spectrophotometry of the flames existing in the combustion chamber. Emission signal during combustion is picked up by an optical sensor with direct access to the combustion chamber, then transmitted using two parallel fiber-optic bundles. The signal can be filtered with set of interference filters and finally it is converted using grating monochromator or photodetector. The main goal of the project is to develop a laboratory diagnostic system enabling on-line identification of the abnormal combustion phenomena like knocking or misfires (lack of combustion). Extracted synthetic quality indexes will be used in the improvement of combustion process and as a feedback signals in the engine control algorithms. The paper is illustrated with some results obtained during previous experiments.

Cycle-by-cycle variations in autonomous and spark assisted homogeneous charge compression ignition combustion of stoichiometric air–fuel mixture

This study investigates cycle-by-cycle variations in a gasoline fuelled, homogeneous charge compression ignition (HCCI) engine with internal exhaust gas recirculation. In order to study the effects of exhaust-fuel reactions occurring prior to the main combustion event fuel was injected directly into the cylinder at two selected timings during the negative valve overlap period. The engine was operated as both autonomous HCCI and spark assisted HCCI (SA-HCCI). The primary interest in this work was the operating region where the engine is switched between HCCI and spark ignition modes, thus operation with stoichiometric air–fuel mixture, which is typical for this region, was considered. Cycle-by-cycle variations in both combustion timing and indicated mean effective pressure (IMEP) were investigated. It was found that long-period oscillations of the IMEP occur when fuel injection is started at early stages of the negative valve overlap period, and that these can be suppressed by delaying the start of injection. This behaviour remained even when fuel injection was split into early and late-negative valve overlap injections. Spark assisted operation allowed eliminating late combustion cycles, thus improving thermal efficiency. However, characteristic patterns of IMEP variations were found to be the same for both HCCI and SA-HCCI operations, irrespective of the adopted negative valve overlap fuel injection strategy, as evidenced by using symbol-sequence statistics.

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.

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.

Laboratory Method of Accelerated Evaluation of Fatigue of Conservatively Treated Teeth

Abstract This paper presents a method of forecasting durability of dental fillings according to the criterion of fatigue expansion of the marginal gap between the filling and the hard tissue of the tooth. The marginal fissure is initiated by the polymer shrinkage of the filling. Development of the marginal fissure results from a number of wear phenomena. The aim of the study was to evaluate the influence of impact mechanical loads (IC) and impact thermal loads (TC) on tightness degradation of dental filling as well as to provide evidence for the necessity of including this type of forces in accelerated laboratory tests of dental filling durability. It has been demonstrated that cyclic thermal shocks and impact mechanical loadings play a crucial role in degradation of the filling. In authors’ opinion, this type of forces should be taken into consideration while performing n vitro tests. Accurate evaluation of the teething conditions, based on quantitative assessment should include the measurements of untightness in all contact zones between the filling and the tooth tissues, and not only by the mastication surface.