Combustion control in gasoline HCCI engine with direct fuel injection and exhaust gas trapping

Homogeneous charge compression ignition (HCCI) seems to be the most promising solution for gasoline engines in the light of future emissions regulations. This novel combustion technique allows for significant reduction of fuel consumption and engine-out NOX emissions at low and medium engine load/speed conditions. High heat release rate enables realization of the Otto cycle close to ideal, increasing thermal efficiency. Among different approaches to invoke an auto-ignition of air-fuel mixture, exhaust gas trapping with the use of a negative valve overlap is under intensive investigations. The paper presents research results ofcontrolling an auto-ignition and combustion phasing in a single cylinder gasoline engine with direct fuel injection operated in the negative valve overlap mode. The experiments were performed at variable valvetrain settings, providing a control of EGR rate and volumetric efficiency. Additionally, the combustion process was investigated at variable air-fuel ratio. It was found that volumetric efficiency and EGR ratę are mainly dependent on exhaust valve timing, while a timing of intake valve determined combustion on-set and its duration. The effects of EGR rate and air-fuel ratio on combustion timing and exhaust gas emissions were isolated. The direct fuel injection showed its benefits versus mixture formation outside the cylinder. The application of variable injection timing provided additional possibility to control the combustion timing and exhaust emissions. However, it was found that the fuel injection strategy should be related to the engine load conditions

Zmienność cykliczna procesu roboczego silnika CAI z wewnętrzną recyrkulacją spalin i bezpośrednim wtryskiem benzyny

Cycle-by-cycle variability in CAI gasoline engine was studied in terms of indicated mean effective pressure and combustion timing variations. Cyclic variability was analyzed for two different engine loads and different injection timings, applied during negative valve overlap. It was found that fluctuations of combustion course and produced indicated work reveal deterministic oscillations, where engine was operated in close to misfire regime. Moreover, kind of correlation between consecutive cycles was found to be affected by fuel injection strategyW pracy przedstawiono analizę zmienności cyklicznej procesu roboczego benzynowego silnika CAI (controlled auto-ignition) przeprowadzoną na podstawie średniego ciśnienia indykowanego oraz przebiegu spalania. badania przeprowadzono dla dwóch wartości obciążenia silnika oraz różnych kątów początku wtrysku paliwa w czasie ujemnego współotwarcia zaworów. Uzyskane wyniki wykazały występowanie zdeterminowanych oscylacji przebiegu kątowego spalania oraz ilości pacy generowanej w cyklu roboczym w warunkach pracy silnika w pobliżu granicy wypadania zapłonów. Ponadto zaobserwowano, że rodzaj korelacji pomiędzy kolejnymi cyklami zależny jest od strategii wtrysku

Application of Ion Current Measurement to Identification of Combustion Parameters in a Homogeneous Charge Compression Ignition Engine

This study examines the application of ion current measurements to the identification of heat release parameters inside the combustion chamber of a homogeneous charge compression ignition (HCCI) engine fuelled with gasoline. HCCI combustion was achieved with the use of exhaust gas trapping. Combustion parameters derived from the in-cylinder pressure and ion current measurements were compared and analysed. Ion current measurements were accomplished using the existing spark plug and a dedicated electronic circuit. The experiments were performed at a variable excess air ratio and a variable amount of trapped residuals. The results showed a good correlation between peak values of the ion current and heat release rate, except for the cases where a fuel-rich mixture was burnt. The computed ion current integral over the volume of the combustion chamber showed a good agreement with the heat released in the combustion chamber, however this parameter was found to be affected by the amount of trapped residuals. Combustion timing characteristic values computed using heat release and ion current were found to be correlated, however the relationship was not linear

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

Detekcja spalania stukowego w silniku o zapłonie iskrowym za pomocą sygnału optycznego z komory spalania

The aim of the presented research was to investigate spectral properties of the combustion flame with special regard to the detection and estimation of intensity of knocking combustion. Research was made using modified single cylinder test engine with spark ignition (SI) equipped with an optical sensor having direct access to the combustion chamber. Measurements were based on wideband intensity of optical radiation and chemiluminescence phenomena occurring in the combustion flame under the influence of high temperature and pressure. Spectral recordings were done for wavelengths typical for emission of intermediate products, covering the range from 250 nm to 625 nm, including typically investigated radicals like C2, CH, CN, OH. Obtained results confirmed, that occurrence and intensity of knock can be determined on the basis of further signal analysis. Comparison with in parallel recorded indicated pressure have shown that characteristics of emitted spectra is more sensitive to the changing of engine operating conditions.Celem prezentowanych badań było zbadanie widmowych własności płomienia w komorze spalania ze specjalnym uwzględnieniem możliwości detekcji i oceny intensywnosci spalania stukowego. Badania zostały wykonane na zmodyfikowanym jednocylindrowym silniku o zapłonie iskrowym (ZI), wyposażonym w optyczny czujnik z bezpośrednim dostępem do komory spalania. W pomiarach wykorzystano zjawiska szerokopasmowej emisji optycznej oraz chemiluminescencji towarzyszące spalaniu mieszanki paliwowopowietrznej. Sygnał optyczny poddawano filtracji, wyodrębniając długości fal typowe dla emsji produktów przejściowych, w zakresie od 250 do 625 nm, obejmującym typowe rodniki takie jak C2, CH, CN oraz OH. Uzyskane rezultaty potwierdziły, że pojawienie się i intensywność spalania stukowego mogą zostać ocenione na podstawie dalszej analizy sygnału zarejestrowanego zarówno w szerokim paśmie promieniowania jak i dla widma chemiluminescencji poszczególnych rodników. Porównanie z rejestrowanym równocześnie przebiegiem ciśnienia pokazało, że emitowane widmo jest bardziej wrażliwe na zmiany warunków pracy silnika

Stanowisko do badań uszczelniającego działania układu tłok–pierścienie–cylinder silnika spalinowego

The paper discusses research assumptions and describes a test stand for the investigations of the sealing properties of the piston rings. The research stand includes an engine brake together with a control system, a research engine and a lubrication and engine thermal state stabilization systems. The engine was fitted with a research piston containing a measuring device enabling the recording of fast varying quantities such as the pressures in the space between the rings, axial displacements of the oil sealing rings in the piston grooves and the temperatures of the gas blown through the seal.W artykule omówiono założenia oraz opisano zbudowane stanowisko do badania zjawisk związanych z uszczelniającym działaniem pakietu pierścieni tłokowych. Stanowisko składa się z hamulca silnikowego wraz z układem sterowania, silnika badawczego oraz układu smarowania i stabilizacji jego stanu cieplnego. Silnik wyposażony jest w tłok badawczy zawierający układ pomiarowy, umożliwiający pomiar i rejestrację szybkozmiennych wielkości, m.in. ciśnień w przestrzeniach międzypierścieniowych, osiowych przemieszczeń pierścieni uszczelniających w rowkach pierścieniowych tłoka oraz temperatur gazu przepływającego przez uszczelnienie

Comperative analysis of emision from engine fuelled with diesel and bio-diesel

The paper presents comparative analysis of operational parameters, smoke emission and toxic components contents in exhaust gases of a compression ignition engine fuelled with fossil diesel, commercial bio-diesel (fatty acid methyl ester) and their blend. Measurements were conducted on an older generation diesel engine equipped with in-line injection pump. Engine was operated in conditions of full load rotational speed characteristic and also ESC steady-state test cycle. Fourier Transform Infrared (FTIR) analytical system provided contents of 23 exhaust gas components. In particular chosen parameters of investigated fuels (on the base of quality reports), performance and fuel consumption characteristic versus rotational speed, smoke emission (D) and content of carbon monoxide (CO), unburned hydrocarbons (THC) and nitrogen oxides (NOx), sulphur dioxide (S02) and carbon dioxide (CO2) in exhaust gas of the engine fuelled with investigated fuels, emission of specific hydrocarbons of the engine fuelled with investigated fuels, of non-regulated compounds measured during the research, molar mass of analyzed exhaust compounds are presented in the paper

Reduction of pressure rise rates in boosted HCCI engine using advanced valve actuation strategies

Homogeneous Charge Compression Ignition (HCCI) is a promising low temperature combustion technology which offers high fuel efficiency and extremely low exhaust emissions. However, there are still some pending issues to be resolved before the technology will achieve mass production level. Namely, combustion controllability should be improved and HCCI operating range should be widen. The latter is constrained by excessive combustion rates under high loads. In this study, advanced variable valve actuation strategies were applied to control auto-ignition timings and combustion rates. The examinations were conducted using single-cylinder research engine fuelled with directly injected gasoline. The HCCI combustion was achieved using negative valve overlap technique. The engine was run under boosted conditions, in an operation regime where acceptable pressure rise rate (PRR) level is usually exceeded. Selected valve timing sweeps were carried out within a scope of the experiments to evaluate PRR reduction potential. The obtained results manifested superior combustion controllability. Late exhaust valve closing enabled reduction of the amount of internally re-circulated exhaust, which propagated to the main event combustion. From the intake side, two effects were observed, i.e. variability of the intake air aspiration and variability of the apparent compression ratio. Both phenomena were found to affect combustion timings and rates

Numerical investigation into the effect of direct fuel injection on thermal stratification in HCCI engine

Despite the fact that HCCI engines are distinguished by mixture homogeneity, some degree of stratification always appears inside a combustion chamber. It is especially applied to residual effect engines utilizing negative valve overlap. Mixture stratification is a result of the imperfect mixing of fresh air with trapped residuals. Direct fuel injection introduces stratification as well, due to fuel vaporization. As a consequence, the temperature within the combustion chamber is uneven. Thermal stratification affects auto-ignition timing and combustion evolution in a high extent. The purpose of this study was to evaluate a degree of thermal stratification in HCCI engine utilizing negative valve overlap. Investigations were performed using three-dimensional CFD model of the combustion system, made by using AVL FIRE software. Simulations were realized for various timings of fuel injection into the cylinder. It was found that fuel injection timing had a significant effect on the thermal stratification and resulting auto-ignition timing