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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

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

Dilution Effects on the Controlled Auto-Ignition (CAI) Combustion of Hydrocarbon and Alcohol Fuels

2001-09-24
2001-01-3606
This paper presents results from an experimental programme researching the in-cylinder conditions necessary to obtain homogenous CAI (or HCCI) combustion in a 4-stroke engine. The fuels under investigation include three blends of Unleaded Gasoline, a 95 RON Primary Reference Fuel, Methanol, and Ethanol. This work concentrates on establishing the CAI operating range with regard to Air/Fuel ratio and Exhaust Gas Re-circulation and their effect on the ignition timing, combustion rate and variability, Indicated thermal efficiency, and engine-out emissions such as NOx. Detailed maps are presented, defining how each of the measured variables changes over the entire CAI region. Results indicate that the alcohols have significantly higher tolerance to dilution than the hydrocarbon fuels tested. Also, variations in Gasoline blend have little effect on any of the combustion parameters measured.
Technical Paper

Performance and Analysis of a 4-Stroke Multi-Cylinder Gasoline Engine with CAI Combustion

2002-03-04
2002-01-0420
Controlled Auto-Ignition (CAI) combustion was realised in a production type 4-stroke 4-cylinder gasoline engine without intake charge heating or increasing compression ratio. The CAI engine operation was achieved using substantially standard components modified only in camshafts to restrict the gas exchange process The engine could be operated with CAI combustion within a range of load (0.5 to 4 bar BMEP) and speed (1000 to 3500 rpm). Significant reductions in both specific fuel consumption and CO emissions were found. The reduction in NOx emission was more than 93% across the whole CAI range. Though unburned hydrocarbons were higher under the CAI engine operation. In order to evaluate the potential of the CAI combustion technology, the European NEDC driving cycle vehicle simulation was carried out for two identical vehicles powered by a SI engine and a CAI/SI hybrid engine, respectively.
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

Control of CAI Combustion Through Injection Timing in a GDI Engine With an Air- Assisted Injector

2005-04-11
2005-01-0134
Controlled auto Ignition (CAI) combustion has great potential for reducing both NOx emissions and fuel consumption in IC engines and the application of direct injection technology to the CAI engine adds another dimension of control to the combustion process. In this work an air-assisted injection system was applied to an engine that used residual gas to initiate and control CAI combustion. Injections were performed at Exhaust valve closure (EVC), intake valve opening (IVO) and BDC of the intake/compression stroke and the effects on combustion phasing (i.e. ignition timing and burn duration), engine output, fuel consumption and exhaust emissions analyzed. Injection at EVC gave the best results in terms of engine output, operating range and combustion stability. Injection at IVO generally resulted in the lowest fuel consumption. It was found that injection timing is an effective means of controlling combustion phasing.
Technical Paper

Numerical Study of Effects of Fuel Injection Timings on CAI/HCCI Combustion in a Four-Stroke GDI Engine

2005-04-11
2005-01-0144
The Controlled Auto-Ignition (CAI) combustion, also known as Homogeneous Charge Compression Ignition (HCCI) was achieved by trapping residuals with early exhaust valve closure in conjunction with direct injection. Multi-cycle 3D engine simulations have been carried out for parametric study on four different injection timings, in order to better understand the effects of injection timings on in-cylinder mixing and CAI combustion. The full engine cycle simulation including complete gas exchange and combustion processes was carried out over several cycles in order to obtain the stable cycle for analysis. The combustion models used in the present study are the Shell auto-ignition model and the characteristic-time combustion model, which were modified to take the high level of EGR into consideration. A liquid sheet breakup spray model was used for the droplet breakup processes.
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

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

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.
Technical Paper

Analysis of a Cost Effective Air Hybrid Concept

2009-04-20
2009-01-1111
The air hybrid engine absorbs the vehicle kinetic energy during braking, stores it in an air tank in the form of compressed air, and reuses it to propel a vehicle during cruising and acceleration. Capturing, storing and reusing this braking energy to give additional power can therefore improve fuel economy, particularly in cities and urban areas where the traffic conditions involve many stops and starts. In order to reuse the residual kinetic energy, the vehicle operation consists of 3 basic modes, i.e. Compression Mode (CM), Expander Mode (EM) and normal firing mode. Unlike previous works, a low cost air hybrid engine has been proposed and studied. The hybrid engine operation can be realised by means of production technologies, such as VVT and valve deactivation. In this work, systematic investigation has been carried out on the performance of the hybrid engine concept through detailed gas dynamic modelling using Ricardo WAVE software.
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

Experimental Investigation of the Effects of Combined Hydrogen and Diesel Combustion on the Emissions of a HSDI Diesel Engine

2008-06-23
2008-01-1787
The effects of load, speed, exhaust gas recirculation (EGR) level and hydrogen addition level on the emissions from a diesel engine have been investigated. The experiments were performed on a 2.0 litre, 4 cylinder, direct injection engine with a high pressure common-rail injection system. Injection timing was varied between 14° BTDC and TDC and injection pressures were varied from 800 bar to 1400 bar to find a suitable base point. EGR levels were then varied from 0% to 40%. Hydrogen induction was varied between 0 and 6% vol. of the inlet charge. In the case of using hydrogen and EGR, the hydrogen replaced air. The load was varied from 0 to 5.4 bar BMEP at two engine speeds, 1500 rpm and 2500 rpm. For this investigation the carbon monoxide (CO), total unburnt hydrocarbons (THC), nitrogen oxides (NOx) and the filter smoke number (FSN) were all measured.
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

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

Diesel Soot Oxidation under Controlled Conditions

2001-09-24
2001-01-3673
A quantitative relationship between diesel soot oxidation rate and oxidation temperature and oxygen partial pressure was investigated by burning the diesel exhaust soot particles in a controlled flat flame supplied with methane/air/oxygen/nitrogen mixtures. The oxidation temperature and the oxygen partial pressure were controlled in the ranges of 1530 to 1820 K and 0.01 to 0.05 atm (1atm = 1.01325 bar) respectively. Soot particle size distribution measurements were achieved with transmission electron microscopy (TEM) for particle samples that were collected on copper grids at different positions along the flame centerline. Oxidation periods were determined by means of laser Doppler anemometry (LDA). The experimental results showed that the experimental oxidation rates fall between the values predicted by the Nagle and Strickland-Constable formula and those by the Lee formula.
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

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

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.
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