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A methodological analysis of combustion parameters and pollutant emissions measuring procedures during transient operation of a D.I. T.C. light duty diesel engine was performed. Combustion process was characterized by ignition delay time, combustion pressure peak value and heat release law measurements during the transient ECE 15 schedule on a dynamic test bed with electronic simulation of inertia. The particulate emission was measured every 0.05 s by an I.R. optical method. In addition some correlations, based on pressure cycle and injection law evolution, were implemented in order to calculate instantaneous fuel delivery and transient NOx emission. Some activities were carried out in order to asses the limits of engine configurations ranking performed with steady state measurements of performances and emissions. Strong differences were detected between carbon emission during transient operations and the value obtained by interpolation from a steady state map.

The effect of external EGR on knock was evaluated using a CFR engine. Combustion pressure was sampled on a time basis. A band pass filter in the time domain was applied to the pressure cycles. Five knock indices were calculated for each combustion cycle. The problem to quantify knock intensity was focused. At this extent measurements were carried out on standard isooctane-n-heptane blends in the test conditions used for the determination of the Motor Method Octane Number (MON). Knock intensity was varied acting on compression ratio. For each index, the conditions of absence of knock were determined using motored cycles. The indices were compared and one of them, showing the lowest C.O.V., was selected for further measurements. The effect of EGR on test fuels having different composition was evaluated varying the compression ratio, at fixed ignition timing. In this way, the same level of detonation, obtained in the absence of EGR, was realized with different amount of external EGR.

A fuel matrix consisting of twelve gasolines was tested in presence of Exhaust Gas Recirculation (EGR). The fuels have different percentages of aromatics (20÷35% vol.), olefins (5÷15% vol.) and oxygen (0÷2% wgt). Four different oxygenated compounds (MTBE, ETBE, TAME, DIPE) were chosen as additives. Tests were carried out on a MPI premixed spark ignition engine at steady operating conditions (2000 rpm, 2 bar BMEP, 13.5% EGR) and stoichiometric air/fuel ratio. Regulated and unregulated pollutants were measured upstream the catalytic converter. Cyclic variation of Indicated Mean Effective Pressure (IMEP) in presence of EGR was also evaluated. The adoption of EGR increases PAH and aldehydes emissions, and decreases benzene emissions of unoxygenated fuels. Conversion efficiencies of CO and of total HC are lowered by EGR. An increase of aromatics content in an unoxygenated fuel leads to higher engine out NOx emission. This effect is reduced if MTBE is added.

Results of an experimental campaign conducted on a multi-hole gasoline injector are used to assess a numerical model for the spray dynamics suitable to be employed for the prediction of a GDI engine pressure cycle. The considered injector generates a spray with a hollow-ellipsoid footprint structure on a plane perpendicular to the spray axis. Spray penetration lengths and cone angles are measured at different injection pressures and total injected masses in an optically accessible vessel containing nitrogen at controlled conditions of temperature and pressure. Injected mass flow rate is measured on a Bosch tube. The numerical simulation is performed within the AVL Fire™ code environment. As a first step, the gasoline is considered as entering a constant volume environment containing nitrogen, in order to reproduce the effected experiments. Measured injection flow rates and cone angles are used as input variables for the model.

The work relates to the use of multidimensional modelling as a tool for improving the robustness of combustion of a Gasoline Direct Injection (GDI) Spark Ignition (SI) engine. A procedure is assessed for the prediction of the thermo-fluid-dynamic processes occurring in a single-cylinder, four-stroke engine, characterised by a bore-to-stroke ratio close to the unity, and a pent-roof head with four valves. The engine is at a design stage, under development for application on two wheels vehicles. A new generation six-holes Bosch injector is considered as realising a jet guided combustion mode. This last is preferred for its potential in realising effective charge stratification and great combustion stability under various operating conditions. The three-dimensional (3D) numerical model is developed within the AVL FIRE™ software environment.

A numerical investigation is performed with the aim of understanding the potential benefits of multiple injections in the mixed mode boosting operation of a Gasoline Direct Injection (GDI) engine. The study is carried out by firstly characterizing a high pressure multi-hole injector from the experimental point of view in the split injection operation. Measurements of the fuel injection rate are made through an AVL Meter operating on the Bosch principle. The injector is tested using gasoline in a double pulse strategy. The injection pressure is varied between 5.0 and 25.0 MPa with the pulse durations calibrated for delivering a total mass up to 50 mg/str. The choice of the dwell time between two successive injection events is achieved by firstly defining the minimum time compatible with the mechanical characteristics of both the injector and the injector driver.

A number of Variable Valve Actuators (VVA) has been recently proposed to improve the performances and the part load efficiency of spark ignition engines. Due to their peculiarity, these systems work with different strategies (late or early inlet valve closing, reduced lift etc.). The shape and the timing of the valve lift affect not only the pumping losses, but also air motion inside the cylinder. That influences mixture formation and combustion evolution of Direct Injection Spark Ignition (DISI) engines. The present paper compares the performances of different VVA systems with the aid of a 1D code for the simulation of the inlet and of the exhaust phases, and of a fluid-dynamic 3D code to evaluate mixing phenomena inside the cylinder.

Three dimensional computations of Diesel combustion were performed using a modified version of Kiva II code. The autoignition and combustion model were tuned on a set of experimental conditions, changing the engine design, the operating conditions and the fuel characteristics. The sensitivity of the model to the different test cases is acceptable and the experimental trends are well reproduced. In addition the peak of pressure and temperature computed by the code are quite close to the experimental values, as well as the pressure derivatives. Once tuned the combustion model constants, different but simple formulations for the soot formation and oxidation processes were implemented in the code and compared with the experimental measurements obtained both with fast sampling technique and two colors method. These formulations were found unable to give good prediction in a large range of engine operating conditions, even if the model tuning may be very good for each test point.

Cetane number, sulphur content and aromatic structure of Automotive Diesel Oil (ADO) were changed to assess their influence on emissions of light duty direct injection Diesel engine. The detailed chemical analysis of particulate soluble fraction allows to quantify the P.A.Hs emission. In addition also the aldehydes and volatile organic compounds were measured in the gaseous phase. The sulphur content of the fuel and its aromatic structure strongly influence particulate emission. The insoluble fraction of the particulate rises with an increase of the high sulphur content ADOs with about the same back end volatility. Unburned P.A.Hs control P.A.Hs emission at the part loads typical of normalized schedules for emission testing of light duty vehicles in Europe. Finally the level of emissions of benzene and 1-3 butadiene is comparable to the total P.A.Hs emission.

Several methods have been proposed to use pressure signal for air/fuel ratio estimation, knock detection and optimal spark timing selection. In this paper some of these methods were compared, and their accuracy and effectiveness was checked. In order to avoid the misleading effects of measurement errors, the comparison was performed using a database of test conditions obtained by means of the WAVE code (Ricardo). New correlations physically based were introduced to evaluate the trapped air mass and the Exhaust Gas Recycling (EGR), cylinder per cylinder. These correlations can give a very important contribution to balance the air-fuel ratio in each cylinder and to improve EGR control strategies.

A simple model of combustion and pollutant formation has been set up. It is part of an engine simulator to be used for the study of engine control strategies. The calculation of inlet and exhaust phases is performed by an emptying and filling method, based on the knowledge of mean inlet and exhaust conditions. A single zone thermodynamic model has been utilized for the calculation of the combustion phase. The values of the shape factors of heat release patterns have been modeled to take into account air/fuel ratio, EGR, load and turbulence at ignition starting. Crevice storage of unburned mixture has been considered as the dominant mechanism for unburned HC production. A model for mixing and burning of HC inside the cylinder has been proposed. NO is calculated using the three steps Zeldovich approach. The model produces realistic calculations of combustion pressure and pollutants emission at various speed, load, ignition timing and EGR.

A commercial four stroke spark ignition engine has been tested at steady conditions, with three different compression ratios, namely: 10, 11.5 and 13. Exhaust Gas Recycle (EGR) has been varied in the range 0% - 20 %. Air/fuel ratio has been maintained at stoichiometric by a closed loop control with Exhaust Gas Oxygen sensor feedback. Significant gains on fuel economy and CO emission index have been achieved at medium and high loads by the simultaneous adoption of EGR and high compression ratios. In these conditions the sum of HC and NOx emission indices attains significant reductions at any load. The tests have shown that EGR allows to avoid knock even at wide open throttle and Maximum Brake Torque timing.