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Technical Paper

In-Cylinder NO-LIF Imaging in a Realistic GDI Engine Using KrF Excimer Laser Excitation

1999-10-25
1999-01-3545
The formation of nitric oxide in a transparent direct injection gasoline engine was studied experimentally using two different schemes of laser-induced fluorescence (LIF) with KrF excimer (248 nm) excitation. With detection of the fluorescence shifted towards the red, strong interference from fluorescence of partially burned fuel was found. With blue-shifted fluorescence, interference was minimized allowing selective detection of NO. Possibilities of quantifying NO fluorescence intensities in inhomogeneous combustion are discussed.
Technical Paper

Hybrid Endoscopes for Laser-Based Imaging Diagnostics in IC Engines

2009-04-20
2009-01-0655
Laser-based in-cylinder diagnostics are well established in engine research. The requirement of large-scale optical accesses, however, makes the application expensive and time consuming. It furthermore limits the engine operation range to low loads and speeds. We introduce laser excitation and imaging optics with a minimal outer diameter of 10 mm (imaging optic) respectively 9 mm (excitation optics). The imaging optics allow the observation of a 30×30 mm2 field with a working distance of 35-42 mm. In order to increase the optical performance diffractive elements are integrated. These elements provide great flexibility for the excitation beam shaping and help to reduce aberrations in the imaging system with a light throughput comparable to imaging setups with standard large-scale UV optics at the same image magnification. We present this miniaturized diagnostic technique based on fuel tracers for measuring fuel density, equivalence ratio and temperature in IC engines.
Technical Paper

Effects of Ignition Timing on CAI Combustion in a Multi-Cylinder DI Gasoline Engine

2005-10-24
2005-01-3720
Having achieved CAI-combustion in a 4-cylinder four-stroke gasoline DI engine the effects of ignition timing on the CAI combustion process were investigated through the introduction of spark. By varying the start of fuel injection, the effects on Indicated Specific values for NOx, HC, CO emissions and fuel consumption were investigated for CAI combustion. The CAI combustion process was then assisted by spark and three different ignition timings were studied. The effect on engine performance and the emission specific values were investigated further. The engine speed was maintained at 1500 rpm and lambda was kept constant at 1.2. It was found that with spark-assisted CAI, IMEP and ISNOx values increased as compared with typical CAI. ISHC values were lower for spark-assisted CAI as compared to typical CAI. Heat release data was studied to better understand this phenomenon.
Technical Paper

The Effect of Spark Ignition on the CAI Combustion Operation

2005-10-24
2005-01-3738
The present paper aims to investigate the influence of spark ignition on CAI combustion based on internal EGR strategy. Controlled Auto-ignition (CAI) combustion is facilitated in a Ricardo single cylinder engine with a pair of special camshafts, which valve lift and cam profile are modified to trap enough hot residuals. Operation regions and other detailed combustion characteristics of the CAI engine operation are analyzed and compared between pure CAI mode and the CAI mode with assisted spark ignition. The results show that spark ignition can play an important role in controlling CAI combustion ignition in low load boundary region. The low temperature chemical reaction process is shortened and the auto ignition timing is advanced due to the spark discharge. Meantime, lower fuel consumption and cycle-to-cycle variations can be achieved.
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

Effects of Bio Diesel Injection in a DI Diesel Engine on Gaseous and Particulate Emission

2005-05-11
2005-01-2204
Vehicles powered by Diesel engines with direct injection contribute to a significant reduction of fuel consumption and CO2 emission. The particulate and gaseous emissions of Diesel engine are of major concern. In order to comply with future legal limits, further developments for the reduction of exhaust gas emissions are required. This work explores the effect of fatty acid methyl ester (FAME) as bio fuel on the emission characteristics of a Diesel engine. The experiments were performed with various fuel combinations such as FAME, FAME/Diesel blends, and water/FAME/Diesel emulsions, which were directly injected into the combustion chamber of a Diesel engine. Due to the complexity of the Diesel engine, several operating parameters were varied to study their influence on the pollutant emissions. The experiments have proved that FAME combustion leads to a significantly reduction of the CO, HC and particle matter compared to Diesel combustion.
Technical Paper

Toluene Laser-Induced Fluorescence (LIF) Under Engine-Related Pressures, Temperatures and Oxygen Mole Fractions

2005-05-11
2005-01-2091
Laser-induced fluorescence (LIF) is frequently used for the investigation of mixing processes in internal engine combustion. Toluene is one of the main fluorescing compounds of commercial gasoline. Understanding its fluorescence properties is therefore crucial for the correct interpretation of signal intensities observed under engine (i.e. high temperature and high pressure) conditions. Toluene LIF signal has been investigated as a function of temperature and oxygen concentration in order to enable quantitative fuel tracer imaging. Signal behavior and interpretation for engine-related conditions is demonstrated based on a semi-empirical fluorescence model. Toluene as well as gasoline-LIF is strongly quenched by oxygen. It has therefore been suggested for a direct measurement of fuel/air equivalence ratios.
Technical Paper

Combustion Characteristics of CAI Combustion with Alcohol Fuels

2010-04-12
2010-01-0843
Due to its potential for simultaneous improvement in fuel consumption and exhaust emissions, controlled autoignition (CAI) combustion has been subject to continuous research in the last several years. At the same time, there has been a lot of interest in the use of alternative fuels in order to reduce reliance on conventional fossil fuels. Therefore, this experimental study has been carried out to investigate the effect of alcohol fuels on the CAI combustion process and on the resulting engine performance. The experimental work was conducted on an optical single cylinder engine with an air-assisted injector. To achieve controlled autoignition, residual gas was trapped in the cylinder by using negative valve overlap and an intake air heater was used to ensure stable CAI combustion in the optical engine. Methanol, ethanol and blended fuels were tested and compared with the results of gasoline.
Journal Article

The Performance Characteristics of an Production Oriented Air Hybrid Powertrain

2010-04-12
2010-01-0821
In a previous paper [ 1 ], the authors have proposed a cost effective air hybrid concept based on a proprietary intake system and cam profile switching (CPS) system [ 2 ]. It was shown through engine simulations that the pneumatic hybrid operation could be achieved with about 15% regenerative efficiency. The proposed air hybrid operation can be achieved with proven technologies and engine components and hence it represents a cost-effective, reliable and quick deployable solution for low carbon vehicles. In this work, a four-cylinder 2 litre diesel engine has been modelled to operate on refined air hybrid engine configurations and the braking and motoring performance of each configuration have been studied. Both air hybrid systems can be constructed with production technologies and incur minimum changes to the existing engine design.
Technical Paper

Improvements of the KIVA Dense Spray Modeling for HSDI Diesel Engines

2007-01-23
2007-01-0001
A numerical study has been performed to investigate the soot emission from a high-speed single-cylinder direct injection diesel engine. It was shown that the current KIVA CFD code with the standard evaporation model could predict the experimental trend, where at a low speed running condition a higher smoke reading is reached when increasing the injector protrusion into the piston chamber and conversely a lower smoke reading was recorded for the same change in injector protrusion at a high running speed condition. Evidence of inappropriate air/fuel mixing was seen via rates of heat release analyses, especially in the high-speed conditions. Efforts to reduce this discrepancy by way of improvements to the KIVA breakup and evaporation models were made. Results of the modified models showed improvements in the vapor dispersion of the atomizing liquid jet, thus affecting the mixing rates and predicted smoke emissions.
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

Control Strategies for Steady and Transient Operation of a 4-Stroke Gasoline Engine with CAI Combustion Using a 4-Variable Valve Actuating System (4VVAS)

2006-04-03
2006-01-1083
In the last few years, residual gas trapping has been widely used to achieve CAI combustion operation in the four-stroke gasoline engine by means of the negative valve overlap period. In this paper, a flexible mechanical variable valve actuation system based on the production technologies is described. The 4VVAS system is capable of independent control of intake valve lift and its timing, exhaust valve lift and its timing and it has been incorporated in a specially designed cylinder head for a single cylinder research engine. In addition, an engine simulation program has been developed to investigate the potential of the 4VVAS system for CAI engine operation and the switch between CAI and SI operations on the same engine. The engine simulation program is written with Matlab Simulink and incorporates an engine block, a newly developed CAI ignition and heat release model, a valve profile generator, and an engine control module for spark ignition and fuelling control.
Technical Paper

Investigation into the Effect of Injection Timing on Stoichiometric and Lean CAI Operations in a 4-Stroke GDI Engine

2006-04-03
2006-01-0417
The Controlled Auto-Ignition (CAI) combustion, also known as Homogeneous Charge Compression Ignition (HCCI) can be achieved by the negative valve overlap method in conjunction with direct injection in a four-stroke gasoline engine. A multi-cycle 3D engine simulation program has been developed and applied to study the effect of injection timing on CAI operations with lean and stoichiometric mixtures. The combustion models used in the present study are based on the modified Shell auto-ignition model and the characteristic-time combustion model. A liquid sheet breakup spray model was used for the droplet breakup processes. Based on the parametric studies on injection timing and equivalence ratio, the major difference between stoichiometric and lean-burn CAI operations is due to the fact that fuel injections take place during the negative valve overlap period.
Technical Paper

The Combustion and Emission Characteristics of Ethanol on a Port Fuel Injection HCCI Engine

2006-04-03
2006-01-0631
With the application of valve timing strategy to inlet and exhaust valves, Homogeneous Charge Compression Ignition (HCCI) combustion was achieved by varying the amount of trapped residuals through negative valve overlap on a Ricardo Hydra four-stroke port fuel injection engine fueled with ethanol. The effect of ethanol on HCCI combustion and emission characteristics at different air-fuel ratios, speeds and valve timings was investigated. The results indicate that HCCI ethanol combustion can be achieved through changing inlet and exhaust valve timings. HCCI ethanol combustion range can be expanded to high speeds and lean burn mixture. Meanwhile, the factors influencing ignition timing and combustion duration are valve timing, lambda and speeds. Moreover, NOx emissions are extremely low under HCCI combustion. The emissions-speed and emissions-lambda relationships are obtained and analyzed.
Technical Paper

Comparison of HCCI Combustion Respectively Fueled with Gasoline, Ethanol and Methanol through the Trapped Residual Gas Strategy

2006-04-03
2006-01-0635
In this paper, HCCI combustion characteristics of three typical high octane number fuels, gasoline, ethanol and methanol, are compared in a Ricardo single cylinder port injection engine with compression ratio of 10.5. In order to trap enough high temperature residual gas to heat intake mixture charge for stable HCCI combustion, camshafts of the experimental engine are replaced by a set of special camshafts with low valve lift and short cam duration. The three fuels are injected into the intake port respectively in different mixture volume percentages, which are E0 (100% gasoline), E50 (50% gasoline, 50% ethanol), E100 (100% ethanol), M50 (50% gasoline, 50% methanol) and M100 (100% methanol). This work concentrates on the combustion and emission characteristics and the available HCCI operation range of these fuels. What's more, the detailed comparison of in-cylinder temperature, ignition timing and other parameters has been carried out.
Technical Paper

Study of SI-HCCI-SI Transition on a Port Fuel Injection Engine Equipped with 4VVAS

2007-04-16
2007-01-0199
A strategy to actualize the dual-mode (SI mode and HCCI mode) operation of gasoline engine was investigated. The 4VVAS (4 variable valve actuating system), capable of independently controlling the intake and exhaust valve lifts and timings, was incorporated into a specially designed cylinder head for a single cylinder research engine and a 4VVAS-HCCI gasoline engine test bench was established. The experimental research was carried out to study the dynamic control strategies for transitions between HCCI and SI modes on the HCCI operating boundaries. Results show that equipped with the 4VVAS cylinder head, the engine can be operated in HCCI or SI mode to meet the demands of different operating conditions. 4VVAS enables the rapid and effective control over the in-cylinder residual gas, and therefore dynamic transitions between HCCI and SI can be stably achieved. It is easier to achieve transition from HCCI to SI than reversely due to the influence of thermo-inertia.
Technical Paper

Developing a Fuel Stratification Concept on a Spark Ignition Engines

2007-04-16
2007-01-0476
A fuel stratification concept has been developed in a three-valve twin-spark spark ignition engine. This concept requires that two fuels or fuel components of different octane numbers (ON) be introduced into the cylinder separately through two independent inlet ports. They are then stratified into two regions laterally by a strong tumbling flow and ignited by the spark plug located in each region. This engine can operate in the traditional stratified lean-burn mode at part loads to obtain a good part-load fuel economy as long as one fuel is supplied. At high loads, an improved fuel economy might also be obtained by igniting the low ON fuel first and leaving the high ON fuel in the end gas region to resist knock. This paper gives a detailed description of developing the fuel stratification concept, including optimization of in-cylinder flow, mixture and combustion.
Technical Paper

In-cylinder Studies of Multiple Diesel Fuel Injection in a Single Cylinder Optical Engine

2005-04-11
2005-01-0915
An experimental study has been carried out on the multiple fuel injection process and its effect on the mixing and combustion in a single cylinder diesel engine with optical access. The engine is equipped with a production type cylinder head and a high pressure common rail fuel system which comprises a directly driven high pressure fuel pump and a control system capable of 8 injections per stroke. The single cylinder optical engine could be operated lubrication-free for up to 5 minutes due to the application of special coating on the piston liner and careful design of the piston and extended cylinder block. The in-cylinder spray and combustion were visualized at 10,000 fps by a high-speed colour video camera and a copper vapour laser. The high-speed video recordings and in-cylinder pressure and heat release analysis for up to four fuel injections will be presented and discussed.
Technical Paper

Development of a Two-Stroke/Four-Stroke Switching Gasoline Engine - The 2/4SIGHT Concept

2005-04-11
2005-01-1137
The pursuit of flexibility is a recurring theme in engine design and development. Engines that are able to switch between the two-stroke operating cycle and four-stroke operation promise a great leap in flexibility. Such 2S-4S engines could then continuously select the optimum operating mode - including HCCI/CAI combustion - for fuel efficiency, emissions or specific output. With recent developments in valvetrain technology, advanced boosting devices, direct fuel injection and engine control, the 2S-4S engine is an increasingly real prospect. The authors have undertaken a comprehensive feasibility study for 2S-4S gasoline engines. This study has encompassed concept and detailed design, design analysis, one-dimensional gas dynamics simulation, three-dimensional computational fluid dynamics, and vehicle simulation. The resulting 2/4SIGHT concept engine is a 1.04 l in-line three-cylinder engine producing 230 Nm and 85 kW.
Technical Paper

Studies of the Control of In-cylinder Inhomogeneities in a 4VVAS Gasoline Engine

2008-04-14
2008-01-0052
In this research, numerical simulation using Star-CD is performed to investigate the mixing process of a single-cylinder experimental gasoline engine equipped with 4VVAS (4 Variable Valve System). Different engine operating conditions are studied with respect to valve parameters, including EVC (Exhaust Valve Closing), IVO (Intake Valve Opening), and IVL (Intake Valve Lift). The definitions of RGF (Residual Gas Fraction)/temperature statistical distribution and inhomogeneity are proposed and quantified, on which the influences of the aforementioned valve parameters are analyzed. Results reveal that, the distribution of in-cylinder residuals varies with valve parameter combinations. Intake valve timing has a greater effect on the in-cylinder distribution and inhomogeneity of residuals than intake valve lift. Earlier IVO leads to lower RGF inhomogeneity around TDC.
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