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This paper describes the application of a non-dispersive infrared-based instrument designed to measure CO with a response time of 7ms. Spark ignition engine emission measurements recorded during the first 505 seconds of an FTP75 drive-cycle for a 4 cylinder engine are presented, including fast response hydrocarbon and NO measurements. An analysis of the engine-out (pre-catalyst) exhaust gas is provided. Data collected simultaneously with a standard emissions test stand and conventional dilution tunnel are compared to the high frequency measurements. Fast CO analysis provides new insight into cold-start fuelling calibration and cylinder-to-cylinder AFR variation. Under rich conditions, the strong dependence of CO production on the quantity of excess fuel allows a significantly faster estimate of engine stoichiometry than a UEGO sensor.

The gaseous and particulate emissions from a diesel passenger car have been studied during cold start and Diesel Particulate Filter (DPF) regeneration events occurring during the New European Drive Cycle (NEDC). During the initial phase of the cycle, Diesel Oxidation Catalyst (DOC) light-off was seen to be highly dynamic with catalyst efficiency changing dramatically with changes in catalyst temperature. Accumulation mode particulate emissions were sampled directly from the exhaust after the DPF. From cold start with a clean (regenerated) DPF, accumulation mode particle emissions were seen to be very much higher than those from a loaded DPF. This accumulation mode slip lasted only approximately 200 seconds. During regeneration of the DPF, the oxidation of trapped soot was associated with a large tailpipe emission of nucleation mode particles.

Using local emissions measurements immediately downstream of a close-coupled catalyst, spatial variations in emissions have been analysed for close-coupled catalysts with different ageing histories. Comparison of the radial emissions profiles between a uniformly-aged (oven-aged) catalyst and two vehicle-aged parts suggests that the vehicle-aged parts have substantial variations in catalyst damage across the radius of the catalyst. The radial variations in damage were confirmed by bench reactor and post-mortem studies. The radial catalyst damage profiles inferred from engine-based evaluations of vehicle aged catalysts show broad correlation with high flow areas identified by CFD predictions and high temperature regions as measured during engine tests.

An improved parameter called “Homogeneity Factor (HF) of in-cylinder charge” has been introduced as a measure to quantify the quality of the air-fuel mixing process in diesel engines. For this purpose, a CFD simulation has been performed to evaluate the effects of Homogeneity Factor on different injection strategies and its correlation with pre mixing process in a common rail DI diesel engine. The results showed a higher Homogeneity Factor will result in higher rate of air-fuel mixing and more complete combustion process. However, the careful adjustment must be made for ideal reduction for both NOx and soot emissions. It was also found when the dwell delay between injection pulses becomes longer, it leaves more time for the air-fuel mixing and initial combustion process of first injection pulse and therefore, the increase of Homogeneity Factor takes place at a later stage and it can caused a reduction of NOx formation.

A study has been conducted to measure the particle number emissions from a current-generation 1.6-liter, Euro IV-compliant turbo-charged Gasoline Direct Injection (GDI) passenger car engine. A fast-response particle size spectrometer was used along with a PMP-compliant particulate measurement system to measure the effect of various engine parameters on the particulate emissions during the New European Drive Cycle (NEDC). Overall particle number is shown along with further analysis of the transient particle emissions. The cold start clearly affects particle formation with approximately 50% of the cumulative particle number being emitted within 200 seconds of the start. Even beyond 200 seconds, the particle number emissions fall as the test progresses and are generally consistent with increases in engine coolant temperature indicating that cold engine fuel preparation issues are contributing to the particle number count.

As the impacts of global warming have become increasingly severe, Oxy-Fuel Combustion (OFC) has been widely considered as a promising solution to reduce Carbon Dioxide (CO2) for achieving net-zero emissions. In this study, a one-dimensional simulation was carried out to study the implementation of OFC technology on a practical turbocharged 4-cylinder Gasoline Direct Injection (GDI) engine with economical oxygen-fuel ratios and commercial gasoline. When the engine is converted from Conventional Air-fuel Combustion (CAC) mode to OFC mode, and the throttle opening, oxygen mass fraction, stoichiometric air-fuel ratio (lambda = 1) are kept constant, it was demonstrated that compared to CAC mode, θF gets a remarkable extension whereas θC is hardly affected. θF and θC are very sensitive to the ignition timing, and Brake Specific Fuel Consumption (BSFC) would benefit significantly from applying Maximum Brake Torque (MBT) ignition timing.

Hydrogen is a reactive species involved with many combustion and catalysis reactions. Traditionally studies on hydrogen relied on theoretical calculation of engine out emissions. This study used a mass spectrometer to measure hydrogen emissions at engine out and tailpipe for a port fuelled injection (PFI) gasoline vehicle. Comparison of measured with calculated for engine out hydrogen showed good agreement. However, catalyst ageing affected post catalyst hydrogen levels to an extent that would be difficult to model by calculation. Study shows that for a detailed understanding of the influence of hydrogen on combustion and catalyst performance the preferred approach is measurement rather than calculation.

The mechanism of NOx and soot reduction using different pilot and multiple injection strategies has been computationally studied in a heavy duty DI Diesel engine. A designed set of advanced injection schemes with various variables and exhaust gas recirculation rate (up to 10%) have been analyzed. The CFD model was firstly calibrated against experimental data for a part load operation at 1600 rpm. The computational models used were found to predict the correct trends obtained in the experiment. The study demonstrated the potential and explained the mechanism of the combination of EGR and multiple injection to reduce both soot and NOx emissions together with improved fuel economy.

Oxyfuel combustion and nitrogen-free combustion coupled with Carbon Capture and Storage (CCS) techniques have been recently proposed as an efficient method to achieve carbon free emissions and to improve the combustion efficiency in diesel engines. In this study, a 3-D computational fluid dynamics model has been used to evaluate the influence of oxyfuel-HCCI combustion on engine operating conditions and combustion characteristics in a HSDI diesel engine. Investigations have conducted using four different diluent strategies based on the volume fraction of pure oxygen and a diluent gas (carbon dioxide). The first series of investigations has performed at a constant fuel injection rating at which 4.4 mg of fuel has injected per cycle. In the second part of analysis, the engine speed was maintained at 1500 rev/min while the engine loads were varied by changing the fuel injection rates in the range of 2.8 to 5.2 mg/cycle.

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.

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.

Diesel homogeneous charge compression ignition (HCCI) engines with early injection can result in significant spray/wall impingement which seriously affects the fuel efficiency and emissions. In this paper, the spray/wall interaction models which are available in the literatures are reviewed, and the characteristics of modeling including spray impingement regime, splash threshold, mass fraction, size and velocity of the second droplets are summarized. Then three well developed spray/wall interaction models, O'Rourke and Amsden (OA) model, Bai and Gosman (BG) model and Han, Xu and Trigui (HXT) model, are implemented into KIVA-3V code, and validated by the experimental data from recent literatures under the conditions related to diesel HCCI engines. By comparing the spray pattern, droplet mass, size and velocity after the impingement, the thickness of the wall film and vapor distribution with the experimental data, the performance of these three models are evaluated.

The effects of Air/Fuel (A/F) ratios and Exhaust Gas Re-Circulation (EGR) rates on Homogeneous Charge Compression Ignition (HCCI) combustion of n-heptane have been experimentally investigated. The experiments were carried out in a single-cylinder, 4-stroke and variable compression-ratio engine equipped with a port fuel injector. Investigations concentrate on the HCCI combustion of n-heptane at different A/F ratios, EGR rates and their effects on knock limit, engine load, combustion variability, and engine-out emissions such as NOx, CO, and unburned HC. Variations of auto-ignition timings and combustion durations in the two-stage combustion process are analyzed in detail. Results show that HCCI combustion with a diesel type fuel can be implemented at room temperature with a conventional diesel engine compression-ratio. However, its knock limit occurs at very high A/F ratios, although high EGR rates can be tolerated.

The emissions performance of a prototype close-coupled catalyst system has been analysed and compared with semi-close-coupled and underfloor systems. Under certain engine conditions during the stabilized region of the ECE Stage 3 drive-cycle, the close-coupled system has showed higher emissions than the semi-close-coupled or underfloor configurations. Using fast response emissions analysers and catalyst warm-up characteristics in conjunction with Computational Fluid Dynamics (CFD), the reasons for this emissions performance deficit has been attributed to flow maldistribution across the front face of the catalyst. Two flow distribution-related mechanisms for emissions breakthrough have been isolated: radial variations in mean AFR (Air-Fuel Ratio) across the catalyst can cause localized emissions breakthrough due to cylinder-to-cylinder AFR variations; and under high space velocity conditions, localized breakthrough can occur due to radial variations in gas velocity through the catalyst.

An accurate prediction of residual burned gas within the combustion chamber is important to quantify for development of modern engines, especially so for those with internally recycled burned gases and HCCI operations. A wall-guided GDI engine has been fitted with an in-cylinder sampling probe attached to a fast response NDIR analyser to measure in-situ the cycle-by-cycle trapped residual gas. The results have been compared with a model which predicts the trapped residual gas fraction based on heat release rate calculated from the cylinder pressure data and other factors. The inlet and exhaust valve timings were varied to produce a range of Residual Gas Fraction (RGF) conditions and the results were compared between the actual measured CO2 values and those predicted by the model, which shows that the RGF value derived from the exhaust gas temperature and pressure measurement at EVC is consistently overestimated by 5% over those based on the CO2 concentrations.

Diesel engine emissions are directly influenced by the air fuel mixture within the cylinder chamber. Increasing concern over the environment impacts of the exhaust pollutants has enforced the setting of emissions legislation since the 1960s. In the last decades emissions legislations have become stricter which resulted to the introduction of multiple injection strategies and exhaust gas recirculation (EGR) in the cylinder in order to abate emissions produced. In this study, the effect of injection rate for double in-cylinder injection in combination with various EGR and bio-diesel fuel rates has been studied using CFD simulations. Taguchi orthogonal arrays have been used for reducing the number of simulations for possible combinations of different rates of injection quantities, EGR composition and bio-diesel quantities. Oneway analysis of variance technique (ANOVA) has been used to estimate the importance of the above factors to the emissions output and performance of the engine.

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.

Effects of split injection with different EGR rate on combustion process and pollutant emissions in a DI diesel engine have been evaluated with CFD modeling. The model was validated with experimental data achieved from a Caterpillar 3401 DI diesel engine and 3D CFD simulation was carried out from intake valve closing (IVC) to exhaust valve opening (EVO). Totally 12 different injection strategies for which two injection pulses with different fuel amount for each pulse (up to 30% for the second pulse) and different separation between two pulses (up to 30° CA) were evaluated. Results show that adequate injection separation and enough fuel amount of the second pulse could form a separate 2nd stage of heat release which could reduce the peak combustion temperature and improve the oxidation of soot formed in the first heat release stage.

An investigation has been carried out to examine the influence of re-entrant combustion chamber geometry on mixture preparation, combustion process and engine performance in a high-speed direct injection (HSDI) four valves 2.0L Ford diesel engine by CFD modeling. The computed cylinder pressure, heat release rate and soot and NOx emissions were firstly compared with experimental data and good agreement between the predicted and experimental values was ensured the accuracy of the numerical predictions collected with the present work. Three ITs (Injection Timing) at 2.65° BTDC, 0.65° BTDC and 1.35° ATDC, all with 30 crank angle pilot separations were also considered to identify the optimum IT for achieving the minimum amount of pollutant emissions.

Tumble and swirl motions in the cylinder of a four-valve SI engine with production type cylinder head were investigated using a cross-correlation digital Particle Image Velocimetry (PIV). Tumble motion was measured on the vertical symmetric plane of the combustion chamber. Swirl motion was measured on a plane parallel to the piston crown with one of intake ports blocked. Large-scale flow behaviours and their cyclic variations were analysed from the measured two-dimensional velocity data. Results show that swirl motion is generated at the end of the intake stroke and persists to the end of the compression stroke. Tumble vortex is produced in the early stage of the compression stroke and distorted in the late stage of the stroke. The cyclic variation of swirl motion is noticeable. The cyclic variation in tumble dominated flow field is much greater.