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Technical Paper

Investigation of CAI Combustion with Positive Valve Overlap and Enlargement of CAI Operating Range

2009-04-20
2009-01-1104
Controlled Auto-Ignition (CAI) combustion was investigated in a Ricardo E6 single cylinder, four-stroke gasoline engine. CAI combustion was achieved by employing positive valve overlap in combination with variable compression ratios and intake air temperatures. The combustion characteristics and emissions were studied in order to understand the major advantages and drawbacks of CAI combustion with positive valve overlap. The enlargement of the CAI operational region was obtained by boosting intake air and adding external EGR. The lean-boosted operation elevated the range of CAI combustion to the higher load region, whilst the use of external EGR allowed the engine to operate with CAI combustion in the region between boosted and N/A CAI operational ranges. The results were analyzed to investigate combustion characteristics, performance and emissions of the boosted CAI operations.
Technical Paper

In-Cylinder Studies of CAI Combustion with Negative Valve Overlap and Simultaneous Chemiluminescence Analysis

2009-04-20
2009-01-1103
The negative valve overlap has been shown as one of the most effective means to achieve controlled autoignition combustion in a four-stroke gasoline engine. A number of researches have been carried out on the performance and emission characteristics of CAI engines but there are still some fundamental questions that are yet to be addressed such as in-cylinder process. In the present study, a Ricardo Hydra single cylinder, four stroke optical gasoline engine was instrumented to investigate CAI combustion through negative valve overlap configuration. The effects of direct fuel injection timings and direct air injection at lambda 1 were studied by means of simultaneous in-cylinder heat release study and high speed images of complete chemiluminescence emission, OH and CHO radicals. In particular, the minor combustion process during the NVO period with various air injection quantities was studied with both heat release analysis and chemiluminescence results.
Technical Paper

Continuous Load Adjustment Strategy of a Gasoline HCCI-SI Engine Fully Controlled by Exhaust Gas

2011-04-12
2011-01-1408
Homogeneous charge compression ignition (HCCI) technology is promising to reduce engine exhaust emissions and fuel consumption. However, it is still confronted with the problem of its narrow operation range that covers only the light and medium loads. Therefore, to expand the operation range of HCCI, mode switching between HCCI combustion and transition SI combustion is necessary, which may bring additional problems to be resolved, including load fluctuation and increasing the complexity of control strategy, etc. In this paper, a continuously adjustable load strategy is proposed for gasoline engines. With the application of the strategy, engine load can be adjusted continuously by the in-cylinder residual gas fraction in the whole operation range. In this research, hybrid combustion is employed to bridge the gaps between HCCI and traditional SI and thus realize smooth transition between different load points.
Technical Paper

Evaluations of Scavenge Port Designs for a Boosted Uniflow Scavenged Direct Injection Gasoline (BUSDIG) Engine by 3D CFD Simulations

2016-04-05
2016-01-1049
The 2-stroke engine has great potential for aggressive engine downsizing due to its double firing frequency which allows lower indicated mean effective pressure (IMEP) and peak in-cylinder pressure with the same output toque compared to the 4-stroke engine. With the aid of new engine technologies, e.g. direct injection, boost and variable valve trains, the drawbacks of traditional 2-stroke engine, e.g. low durability and high emissions, can be resolved in a Boosted Uniflow Scavenged Direct Injection Gasoline (BUSDIG) engine. Compared to the loop-flow or cross-flow engines, the BUSDIG engine, where intake ports are integrated to the cylinder liner and controlled by the movement of piston top while exhaust valves are placed in the cylinder head, can achieve excellent scavenging performance and be operated with high boost.
Technical Paper

Experimental Comparison between Stratified Flame Ignition and Micro Flame Ignition in a Gasoline SI-CAI Hybrid Combustion Engine

2017-03-28
2017-01-0737
Controlled Auto-Ignition (CAI), also known as Homogeneous charge compression ignition (HCCI), has been the subject of extensive research because of their ability to providing simultaneous reduction in fuel consumption and NOx emissions in a gasoline engine. However, due to its limited operation range, combustion mode switching between CAI and spark ignition (SI) combustion is essential to cover the overall operational range of a gasoline engine for passenger car applications. Previous research has shown that the SI-CAI hybrid combustion has the potential to control the ignition timing and heat release process during both steady state and transient operations. However, it was found that the SI-CAI hybrid combustion process is often characterized with large cycle-to-cycle variations, due to the flame instability at high dilution conditions.
Technical Paper

Study of Flame Speed and Knocking Combustion of Gasoline, Ethanol and Hydrous Ethanol (10% Water) at Different Air/Fuel Ratios with Port-Fuel Injection

2018-04-03
2018-01-0655
In this paper, an experimental study was performed to investigate characteristics of flame propagation and knocking combustion of hydrous (10% water content) and anhydrous ethanol at different air/fuel ratios in comparison to RON95 gasoline. Experiments were conducted in a full bore overhead optical access single cylinder port-fuel injection spark-ignition engine. High speed images of total chemiluminescence and OH* emission was recorded together with the in-cylinder pressure, from which the heat release data were derived. The results show that under the stoichiometric condition anhydrous ethanol and wet ethanol with 10% water (E90W10) generated higher IMEP with at an ignition timing slightly retarded from MBT than the gasoline fuel for a fixed throttle position. Under rich and stoichiometric conditions, the knock limited spark timing occurred at 35 CA BTDC whereas both ethanol and E90W10 were free from knocking combustion at the same operating condition.
Technical Paper

Experimental Investigation of Combustion and Emission Characteristics of Stoichiometric Stratified Flame Ignited (SFI) Hybrid Combustion in a 4-Stroke PFI/DI Gasoline Engine

2019-04-02
2019-01-0960
Controlled Auto-Ignition (CAI), also known as Homogeneous Charge Compression Ignition (HCCI), can improve the fuel economy of gasoline engines and simultaneously achieve ultra-low NOx emissions. However, the difficulty in combustion phasing control and violent combustion at high loads limit the commercial application of CAI combustion. To overcome these problems, stratified mixture, which is rich around the central spark plug and lean around the cylinder wall, is formed through port fuel injection and direct injection of gasoline. In this condition, rich mixture is consumed by flame propagation after spark ignition, while the unburned lean mixture auto-ignites due to the increased in-cylinder temperature during flame propagation, i.e., stratified flame ignited (SFI) hybrid combustion.
Technical Paper

Dilution Boundary Expansion Mechanism of SI-CAI Hybrid Combustion Based on Micro Flame Ignition Strategy

2019-04-02
2019-01-0954
In decade years, Spark Ignition-Controlled Auto Ignition (SI-CAI) hybrid combustion, also called Spark Assisted Compression Ignition (SACI) has shown its high-efficiency and low emissions advantages. However, high dilution causes the problem of unstable initial ignition and flame propagation, which leads to high cyclic variation of heat release and IMEP. The instability of SI-CAI hybrid combustion limits its dilution degree and its ability to improve the thermal efficiency. In order to solve instability problems and expand the dilution boundary of hybrid combustion, micro flame ignition (MFI) strategy is applied in gasoline hybrid combustion engines. Small amount of Dimethyl Ether (DME) chosen as the ignition fuel is injected into cylinder to form micro flame kernel, which can stabilize the ignition combustion process.
Technical Paper

The Application of Controlled Auto-Ignition Gasoline Engines -The Challenges and Solutions

2019-04-02
2019-01-0949
Controlled Auto-Ignition (CAI) combustion, also known as Homogeneous Charge Compression Ignition (HCCI), has the potential to simultaneously reduce the fuel consumption and nitrogen oxides emissions of gasoline engines. However, narrow operating region in loads and speeds is one of the challenges for the commercial application of CAI combustion to gasoline engines. Therefore, the extension of loads and speeds is an important prerequisite for the commercial application of CAI combustion. The effect of intake charge boosting, charge stratification and spark-assisted ignition on the operating range in CAI mode was reviewed. Stratified flame ignited (SFI) hybrid combustion is one form to achieve CAI combustion under the conditions of highly diluted mixture caused by the flame in the stratified mixture with the help of spark plug.
Technical Paper

Study of Polycyclic Aromatic Hydrocarbons Evolution Processing in GDI Engines Using TRF-PAH Chemical Kinetic Mechanism

2016-04-05
2016-01-0690
In the present study, we developed a reduced TRF-PAH chemical reaction mechanism consisted of iso-octane, n-heptane and toluene as gasoline surrogate fuels for GDI (gasoline direct injection) spark ignition engine combustion simulation. The reduced mechanism consists of 85 species and 232 reactions including 17 species and 40 reactions related to the PAHs (polycyclic aromatic hydrocarbons) formation. The present mechanism was validated for extensive validations with experimental ignition delay times in shock tubes and laminar flame speeds in flat flame adiabatic burner for gasoline/air and TRF/air mixtures under various pressures, temperatures and equivalence ratios related to engine conditions. Good agreement was achieved for most of the measurement. Mole fraction profiles of PAHs for n-heptane flame were also simulated and the experimental trends were reproduced well. The vapor-phase and particulate-bound PAHs existed in GDI engine exhaust were sampled and analyzed by GC-MS.
Technical Paper

Computational Study of the Effects of the Re-entrant Lip Shape and Toroidal Radii of Piston Bowl on a HSDI Diesel Engine's Performance and Emissions

2004-03-08
2004-01-0118
The piston bowl design is one of the most important factors that affect the air/fuel mixing and the subsequent combustion and pollutant formation processes in a direct injection diesel engine. The bowl geometry and dimensions, such as pip region, bowl lip area, and torus radius are all known to have an effect on the in-cylinder mixing and combustion process. In order to understand better the effect of torus radius, three piston bowls with different torus radius and lip shapes designs but with the same lip area and pip inclination were investigated using Computational Fluid Dynamics (CFD) engine modelling. KIVA3V with improved sub-models was used to model the in-cylinder flows and combustion process, and it was validated on a High-Speed Direct Injection (HSDI) engine with a 2nd generation common rail fuel injection system.
Technical Paper

An Experimental Study on HCCI Combustion in a Four-Stroke Gasoline Engine with Reduced Valve Lift Operations

2005-10-24
2005-01-3736
To achieve homogeneous charge compression ignition (HCCI) combustion in the range of low speeds and loads, special camshafts with low intake/exhaust cam lift and short intake/exhaust cam duration were designed. The camshafts were mounted in a Ricardo Hydra four-stroke single cylinder port fuel injection gasoline engine. HCCI combustion was achieved by controlling the amount of trapped residuals from previous cycle through negative valve overlap. The results show that indicated mean effective pressure (IMEP) depends on valve timings, engine speeds and lambda. Early exhaust valve closing (EVC) timings result in high residual fractions in the cylinder and low air mass sucked into the cylinder. As a result, combustion duration increases, IMEP and peak pressure decrease. However, pumping losses decrease. High engine speed has the similar effect on HCCI combustion characteristics as early EVC timings do. But inlet valve opening timings have slight effect on IMEP compared to EVC timings.
Technical Paper

Parametric Study on CAI Combustion in a GDI Engine with an Air-Assisted Injector

2007-04-16
2007-01-0196
Controlled auto-ignition (CAI) combustion and engine performance and emission characteristics have been intensively investigated in a single-cylinder gasoline direct injection (GDI) engine with an air-assisted injector. The CAI combustion was obtained by residual gas trapping. This was achieved by using low-lift short-duration cams and early closing the exhaust valves. Effects of EVC (exhaust valve closure) and IVO (intake valve opening) timings, spark timing, injection timing, coolant temperature, compression ratio, valve lift and duration, on CAI combustion and emissions were investigated experimentally. The results show that the EVC timing, injection timing, compression ratio, valve lift and duration had significant influences on CAI combustion and emissions. Early EVC and injection timing, higher compression ratio and higher valve lift could enhance CAI combustion. IVO timing had minor effect on CAI combustion.
Technical Paper

Investigation into Controlled Auto-Ignition Combustion in a GDI Engine with Single and Split Fuel Injections

2007-04-16
2007-01-0211
A multi-cycle three-dimensional CFD engine simulation programme has been developed and applied to analyze the Controlled autoignition (CAI) combustion, also known as homogeneous charge compression ignition (HCCI), in a direct injection gasoline engine. CAI operation was achieved through the negative valve overlap method by means of a set of low lift camshafts. The effect of single injection timing on combustion phasing and underlying physical and chemical processes involved was examined through a series of analytical studies using the multi-cycle 3D engine simulation programme. The analyses showed that early injection into the trapped burned gases of a lean-burn mixture during the negative valve overlap period had a large effect on combustion phasing, due to localized heat release and the production of chemically reactive species. As the injection was retarded to the intake stroke, the charge cooling effect tended to slow down the autoignition process.
Technical Paper

Effect of Injection Timing on Mixture and CAI Combustion in a GDI Engine with an Air-Assisted Injector

2006-04-03
2006-01-0206
The application of controlled auto-ignition (CAI) combustion in gasoline direct injection (GDI) engines is becoming of more interest due to its great potential of reducing both NOx emissions and fuel consumption. Injection timing has been known as an important parameter to control CAI combustion process. In this paper, the effect of injection timing on mixture and CAI combustion is investigated in a single-cylinder GDI engine with an air-assisted injector. The liquid and vapour phases of fuel spray were measured using planar laser induced exciplex fluorescence (PLIEF) technique. The result shows that early injection led to homogeneous mixture but late injection resulted in serious stratification at the end of compression. CAI combustion in this study was realized by using short-duration camshafts and early closure of the exhaust valves. During tests, the engine speed was varied from 1200rpm to 2400rpm and A/F ratio from stoichiometric to lean limit.
Technical Paper

CAI Combustion with Methanol and Ethanol in an Air-Assisted Direct Injection SI Engine

2008-06-23
2008-01-1673
CAI combustion has the potential to be the most clean combustion technology in internal combustion engines and is being intensively researched. Following the previous research on CAI combustion of gasoline fuel, systematic investigation is being carried out on the application of bio-fuels in CAI combustion. As part of an on-going research project, CAI combustion of methanol and ethanol was studied on a single-cylinder direct gasoline engine with an air-assisted injector. The CAI combustion was achieved by trapping part of burnt gas within the cylinder through using short-duration camshafts and early closure of the exhaust valves. During the experiment the engine speed was varied from 1200rpm to 2100rpm and the air/fuel ratio was altered from the stoichiometry to the misfire limit. Their combustion characteristics were obtained by analysing cylinder pressure trace.
Technical Paper

In-cylinder Studies of Fuel Injection and Combustion from a Narrow Cone Fuel Injector in a High Speed Single Cylinder Optical Engine

2008-06-23
2008-01-1789
Over the last decade, the high speed direct injection (HSDI) diesel engine has made dramatic progress in both its performance and market share in the light duty vehicle market. However, with ever more stringent emission legislation to be introduced over coming years, the simultaneous reduction of NOx and Particulate Matter (PM) from the HSDI diesel engine is being intensively researched. As part of a European Union (EU) NICE integrated project, research has been carried out to investigate the fuel injection and combustion from a narrow cone fuel injector in a high speed direct injection single cylinder engine with optical access utilising a multiple injection strategy and various alternate fuels. The fuel injection process was visualised using a high speed imaging system comprising a copper vapour laser and a high speed video camera. The auto-ignition and combustion process was analysed through the chemiluminescence images of CHO and OH using an intensified CCD camera.
Technical Paper

Computational Study of the Effects of Injection Timing, EGR and Swirl Ratio on a HSDI Multi-Injection Diesel Engine Emission and Performance

2003-03-03
2003-01-0346
Reductions in fuel consumption, noise level, and pollutant emissions such as, Nitrogen Oxide (NOX) and Particulate Matter (PM), from direct-injection (DI) diesel engines are important issues in engine research. To achieve these reductions, many technologies such as high injection pressure, multiple injection, retarded injection timing, EGR, and high swirl ratio have been used in high-efficiency DI diesel engines in order to achieve combustion and emission control. However, each technology has its own advantages and disadvantages, and there is a very strong interaction between these methods when they are simultaneously used in the engine. This study presents a computational study of both the individual effect and their interactions of injection timing, EGR and swirl ratio separately and their interaction in a HSDI common rail diesel engine using the KIVA-3V code.
Technical Paper

Evaluating the EGR-AFR Operating Range of a HCCI Engine

2005-04-11
2005-01-0161
We present a computational tool to develop an exhaust gas recirculation (EGR) - air-fuel ratio (AFR) operating range for homogeneous charge compression ignition (HCCI) engines. A single cylinder Ricardo E-6 engine running in HCCI mode, with external EGR is simulated using an improved probability density function (PDF) based engine cycle model. For a base case, the in-cylinder temperature and unburned hydrocarbon emissions predicted by the model show a satisfactory agreement with measurements [Oakley et al., SAE Paper 2001-01-3606]. Furthermore, the model is applied to develop the operating range for various combustion parameters, emissions and engine parameters with respect to the air-fuel ratio and the amount of EGR used. The model predictions agree reasonably well with the experimental results for various parameters over the entire EGR-AFR operating range thus proving the robustness of the PDF based model.
Technical Paper

Effects of Injection Timing and Valve Timings on CAI Operation in a Multi-Cylinder DI Gasoline Engine

2005-04-11
2005-01-0132
CAI-combustion was achieved in a 4-cylinder four-stroke gasoline DI engine, with all cylinders running in CAI-mode. Standard components were used, with the exception of the camshafts which had been modified in order to restrict the gas exchange process. Results shown in the paper are between a load of 1.45 - 2.65 bar, an engine speed of 1500rpm and at a lambda value of 1.2. As is typical with this type of combustion, reductions in emissions of NOx were recorded as well as a slight decrease in HC emissions, also there was a reduction in the brake specific fuel consumption. The effect that injection timing on factors such as start of combustion, combustion duration and heat release rate are also investigated.
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