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Heat transfer in the combustion chamber of s.i. engines operating under knocking conditions has been detected and analyzed. Measurements have been carried out, cycle by cycle, on a CFR laboratory engine by means of a dedicated instrument and an original method. The relationship between heat transfer and knock intensity has been analyzed on a statistical basis, emphasizing knock intensity influence on heat transfer distribution. Moreover, the share of heat transfer more closely related to knock intensity has been highlighted: heat transfer is shown not to be significantly affected by knock intensity under light-to-medium knock conditions; on the contrary, the influence becomes evident under medium-to-heavy knock conditions. Eventually, heat transfer indexes influenced by knock intensity have been evaluated, allowing a comparison of knock-related thermal properties of fuels.

The worldwide trend to increasingly stringent exhaust emissions standards, together with consumer requirements, are forcing both vehicle and engine manufacturers, as well as manufacturers of ancilliary equipment, to introduce new and often novel technology in order to produce clean, quiet and socially acceptable transport at affordable prices. The combustion process lies at the heart of the engine and the quality of the combustion determines the acceptability of the product to a very large extent. The fuel injection system plays a large role in the combustion process and in consequence, the fuel system type and capabilities strongly influence the performance of the combustion system. There has never been such a range of fuel injection systems available at one time as there is today. High pressure hydraulically actuated systems /1/ compete with cam driven fuel injection systems /2/ to deliver the injection requirements demanded by the vehicles both of today and in the future.

The influence of fuel density on exhaust emissions from diesel engines has been investigated in a number of studies and these have generally concluded that particulate emissions rise with increasing density This paper reviews recent work in this area, including the European Programme on Emissions, Fuels and Engine Technologies (EPEFE) and reports on a complementary study conducted by CONCAWE, in cooperation with AVL List GmbH The project was carried out with a passenger car equipped with an advanced technology high speed direct injection turbocharged / intercooled diesel engine fitted with a complex engine management system which was referenced to a specific fuel density This production model featured electronic diesel control, closed loop exhaust gas recirculation and an exhaust oxidation catalyst Tests were carried out with two EPEFE fuels which excluded the influence of key fuel properties other than density (828 8 and 855 1 kg/m3) Engine operation was adjusted for changes in fuel density by resetting the electronic programmable, read-only memory to obtain the same energy output from the two test fuels In chassis dynamometer tests over the ECE15 + EUDC test cycle the major impact of fuel density on particulate emissions for advanced engine technology/engine management systems was established A large proportion of the density effect on particulate and NOx emissions was due to physical interaction between fuel density and the electronic engine management system Limited bench engine testing of the basic engine showed that nearly complete compensation of the density effect on smoke (particulate) emissions could be achieved when no advanced technology was applied

This paper intends to analyze the simultaneous impact of speed and acceleration on exhaust pollutant emissions. For this purpose, actual driving recording were used. Kinematic sequences were randomly selected amongst the recorded data, in order to constitute a representative set of driving conditions. For each sequence, average levels of speed and positive acceleration were calculated. Instantaneous and integrated pollutant emissions were calculated using an existing emission model, developed for calculating pollutant emissions and fuel consumption as functions of instantaneous speed and acceleration. This model is based on instantaneous emission measurements on a chassis dynamometer using actual driving cycles, over a sample of 150 European cars. Emissions of CO, CO2, HC, NOx were analyzed considering the average speed and positive acceleration, for different categories of vehicles Diesel, conventional and catalyst vehicles.

The variation of turbulent flow quantities with engine speed has been investigated in the combustion chamber of an automotive diesel engine with a high-squish conical-type in-piston bowl and one helicoidal intake duct, at speeds covering the wide range of 600-3000 rpm, under motored conditions. The investigation had the main purpose of studying the engine speed effect on the structure of both cycle-resolved and conventional turbulence over the induction, the compression and the early stage of the expansion stroke. The low frequency component of the fluctuating motion was also investigated.

This work has been carried out on a two-cylinder s.i. automotive engine and it investigates spark advance, air-fuel ratio and variable valve overlap for low emissions and low fuel consumption, with an acceptable cyclic irregularity under idle conditions. An original application of a variable valve timing system, based on a passive electro-hydraulic link, has been used for this purpose. The instantaneous engine speed and in-cylinder pressure have been measured and recorded by means of an acquisition data system that allows both the determination and the comparison of some cyclic irregularity indexes, under different engine settings, at idle. The optimum spark advance, air-fuel ratio and valve overlap, which yield the best compromise between fuel consumption and cyclic irregularity, under idle operating conditions, have therefore been pointed out.

Recent developments have raised increased interest on the concept of gasoline direct injection as the most promising future strategy for fuel economy improvement of SI engines. The general requirements for mixture preparation and combustion systems in a GDI engine are presented in view of known and actual systems regarding fuel economy and emission potential. The characteristics of the actually favored injection systems are discussed and guidelines for the development of appropriate combustion systems are derived. The differences between such mixture preparation strategies as air distributed fuel and fuel wall impingement are discussed, leading to the alternative approach to the problem of mixture preparation with the fully air distributing concept of direct mixture injection.

The paper describes a feasibility test program on a 2 liter, 4 cylinder DI/TCI passenger car engine operated on the new alternative fuel Dimethyl Ether (DME, CH3 - O - CH3) with the aim of demonstrating its potential of meeting ULEV emissions (0.2 g/mi NOx in the FTP 75 test cycle) when installed in a full size passenger car. Special attention is drawn to the fuel injection equipment (FIE) as well as combustion system requirements towards the reduction of NOx and combustion noise while keeping energetic fuel consumption at the level of the baseline DI/TCI diesel engine. FIE and combustion system parameters were optimized on the steady state dynamometer by variation of a number of parameters, such as rate of injection, number of nozzle holes, compression ratio, piston bowl shape and exhaust gas recirculation.

A new test bench has been set up and equipped in order to analyze the air mean motion and turbulence quantities in the combustion system of an automotive diesel engine with one helicoidal intake duct and a conical type in-piston bowl. A sophisticated HWA technique employing single- and dual-sensor probes was applied to the in-cylinder flow investigation under motored conditions. The anemometric probe was also operated as a thermometric sensor. An analytical-numerical procedure, based on the heat balance equations for both anemometric and thermometric wires, was refined and applied to compute the gas velocity from the anemometer output signal. The gas property influence, the thermometric sensor lag and the prong temperature effects were taken into account with this procedure. The in-cylinder velocity data were reduced using both a cycle-resolved approach and the conventional ensemble-averaging procedure, in order to separate the mean flow from the fluctuating motion.

In order to facilitate the analysis of SI engine combustion phenomena, we have developed a fiber optic system which allows the observation of combustion in essentially standard engines. Optical access to the combustion chamber is achieved with micro-optic elements and optical fibers in the cylinder head gasket. Each fiber views a narrow cone of the combustion chamber and transmits the light seen within this acceptance cone to the detector and recorder unit. A large number of such fiber optic detectors have been incorporated in a cylinder head gasket and this multichannel system was arranged in a geometric configuration which allowed the reconstruction of the spatial flame intensity distribution within the observed combustion chamber cross-section. The spatial information was gained from the line-of-sight intensity signals by means of a tomographic reconstruction technique.

The results of an experimental study on the statistical structure of turbulence in an automotive engine are reported, with specific reference to the time-frequency domains. Autocorrelation and autospectral density coefficients were evaluated in consecutive crank-angle intervals throughout the induction and compression strokes. Eulerian time scales were obtained on the analogy of both the micro and integral time scales of turbulence for stationary flows. The spatial distribution of the turbulence structure was investigated in the combustion chamber of a diesel engine with a shallow in-piston bowl and two tangential intake ducts. The study was carried out for different swirl flow conditions, produced by deactivating one intake duct and/or by changing the engine speed. The velocity data were acquired using an advanced HWA technique, under motored conditions.

The combined requirement of achieving CAFE values between 32 to 38 mpg plus LEV/ULEV emission standards to comply with US legal requirements between 1995 and 2000 represents the most demanding challenge for engine engineering. Thus all possible methods of engine improvement towards fuel economy and emissions have to be considered. Besides using new ideas also the methods of engine development have to be modernized to cope with the challenge. The paper presents advanced combustion and exhaust gas aftertreatment systems which combine high power output, favourable torque characteristics and high fuel economy with the potential for obtaining LEV/ULEV emission values, as well as improved development techniques.

A detailed investigation of the influence of intake port design on the in-cylinder flow structure during the intake and compression strokes, the mixing of the residual gas and a non-premixed intake charge, and the extent and pattern of charge inhomogenity near the time of combustion is described. The engine geometry is typical of the current lean-burn design and the study includes comparison of a helical (swirl) port and an idealized direct (no swirl) port designs. The results show marked dependence of the in-cylinder charge mixing characteristics on the intake port design. It is found that combinations of intake port design and manifold fuel injection timing produce favourably-stratified or irregularly-mixed charge distributions at the time of spark ignition. The consequences with respect to combustion characteristics are pointed out.