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The use of gaseous fuels in internal combustion engines is increasing, due to several reasons, first of all their low environmental impact, large availability and low cost. Nevertheless, the need to reduce emissions also from gas engines is an important aspect to be considered in order to comply with future engine emissions regulations. In this scenario, an extensive experimental activity was performed to fully characterize an heavy duty spark ignition engine, under development for Euro VI compliance and designed to run with gaseous fuels. Two separate sets of experiments were carried out, in order to analyze the engine behavior when burning LPG and CNG, respectively. To this aim, the engine was installed on a dynamic test bench, accurately instrumented to characterize the combustion evolution, performance and exhaust pollutant emissions, along the World Harmonized Transient Cycle (WHTC), the new European driving homologation cycle.

Computations were carried out to simulate in-cylinder flow field and mixture preparation of a small port scavenged direct-injection two-stroke spark-ignition engine using a modified version of KIVA-3 code. Simulations of the interaction between air flow and fuel were performed on a commercial Piaggio (125 cc) motorcycle engine modified to operate with a hollow-cone injector located in different positions of the dome-shaped combustion chamber. The engine has a large exhaust port and five smaller transfer ports connecting the cylinder to the crankcase. The numerical grid of this complex geometry was obtained using an IBM grid generator based on the output of engine design by CATIA solution. To take into account the rapid distortion of flow, the standard k-ε turbulence model in KIVA-3 was replaced by the RNG k-ε model.

Tangential component of velocity and turbulence were measured in three locations in the re-entrant combustion chamber of a motored single-cylinder d.i. Diesel engine (0.435 liter, 21:1 compression ratio) using a Laser Doppler Velocimetry system. Moreover, a modified LDV system with two-probe volume was used to measure directly lateral integral length scales of the velocity tangential component at two engine speeds. The measurements were made on a horizontal plane at 5 mm below the engine head from 100 degrees before TDC to 60 degrees after TDC of both the compression and expansion strokes. The engine was motored at 1,000 and 1,500 rpm respectively. An ensemble-averaging technique was performed to analyze the instantaneous velocity information supplied by two Burst Spectrum Analyzers. The lateral integral length scale was obtained from the integral of the spatial correlation coefficient of the velocity fluctuation for different separation.

The present paper aims at developing a general method to estimate integral and microtime scales of turbulent in-cylinder flow field in reciprocating engines. The ensemble average technique was used to compute the integral time scale from the single point time autocorrelation function, whereas the microtime scale, representative of the most rapid changes that occur in the fluctuation, was computed as the intercept of the parabola that matches the autocorrelation function at the origin. Further, the microtime scale was also estimated by spectral analysis through the energy spectral density function of the ensemble turbulent fluctuation and the results obtained by the two methods were compared. The procedures were applied to the tangential component of the instantaneous velocity data collected, at different engine speeds (1,000, 1,500, 2,000 rpm), within a motored d.i. diesel engine equipped with a re-entrant combustion chamber, using the Laser Doppler Anemometry (LDA) technique.

The fluid-mechanic behaviour of straight-sided and re-entrant chamber geometries has been studied using laser doppler anemometry (LDA) technique. Measurements have been carried out during the compression stroke in a direct injection diesel engine, representative of medium size family, operating at 1000 rpm under motored conditions. The mean motion and turbulence intensity have been computed using a filtering procedure on the LDA data. Using the second version of KIVA code, the air flow field evolution during the same crank angle period has been also computed. To perform proper comparisons between measured and computed values of mean velocity and turbulence intensity, a careful choice of the initial conditions for computations has been performed. Reasonable agreement has been found between computed and measured mean swirl velocities for both combustion chamber geometries tested. On the contrary, the computed turbulence intensities underestimate those measured.

This paper presents results of an experimental investigation on a flexible port dual fuel injection using different ethanol to gasoline mass fractions. A four stroke, two cylinder turbocharged SI engine was used for the experiments. The engine speed was set at 3000 rpm, tests were carried out at medium-high load and two air-fuel-ratio. The initial reference conditions were set running the engine, fueled with full gasoline at the KLSA boundary, in accordance with the standard ECU engine map. This engine point was representative of a rich mixture (λ=0.9) in order to control the knock and the temperature at turbine inlet. The investigated fuels included different ethanol-gasoline mass fractions (E10, E20, E30 and E85), supplied by dual injection within the intake manifold. A spark timing sweep, both at stoichiometric and lean (λ=1.1) conditions, up to the most advanced one without knock was carried out.

In this work, a promising technique, consisting of a liquid Water Injection (WI) at the intake ports, is investigated to overcome over-fueling and delayed combustions typical of downsized boosted engines, operating at high loads. In a first stage, experimental tests are carried out in a spark-ignition twin-cylinder turbocharged engine at a fixed rotational speed and medium-high loads. In particular, a spark timing and a water-to-fuel ratio sweep are both specified, to analyze the WI capability in increasing the knock-limited spark advance. In a second stage, the considered engine is schematized in a 1D framework. The model, developed in the GT-Power™ environment, includes user defined procedures for the description of combustion and knock phenomena. Computed results are compared with collected data for all the considered operating conditions, in terms of average performance parameters, in-cylinder pressure cycles, burn rate profiles, and knock propensity, as well.

In this paper, an experimental and numerical analysis of combustion process and knock occurrence in a small displacement spark-ignition engine is presented. A wide experimental campaign is preliminarily carried out in order to fully characterize the engine behavior in different operating conditions. In particular, the acquisition of a large number of consecutive pressure cycle is realized to analyze the Cyclic Variability (CV) effects in terms of Indicated Mean Effective Pressure (IMEP) Coefficient of Variation (CoV). The spark advance is also changed up to incipient knocking conditions, basing on a proper definition of a knock index. The latter is estimated through the decomposition and the FFT analysis of the instantaneous pressure cycles. Contemporary, a quasi-dimensional combustion and knock model, included within a whole engine one-dimensional (1D) modeling framework, are developed. Combustion and knock models are extended to include the CV effects, too.

The OpenFOAM® CFD methodology is nowadays employed for simulation in internal combustion engines and a lot of work has been done for an appropriate description of all complex phenomena. At the moment in the RANS turbulence models available in the OpenFOAM® toolbox the turbulence modulation is not yet included, and the present work analyzes the predictive capabilities of the code in simulating high injection pressure fuel sprays after modeling the influence of the dispersed phase on the turbulence structure. Different experiments were employed for the validation. At first, non-evaporating diesel spray was considered in a constant volume and quiescent vessel. The validation was performed via the available experimental spray evolution in terms of penetrations and spatial/temporal fuel distributions. Then the Sandia combustion chamber was chosen for diesel spray simulation in non-reacting conditions.

In-cylinder measurements of turbulent integral length scales, carried out during the last 60 degrees of the compression stroke at 600 and 1,000 rpm by a two-probe volume LDV system, were used to assess the capability of the k-ε model used in KIVA-II code. The objective of the paper is to address the following question: what is the most reasonable definition of turbulent length scale in the k-ε model for engine applications? The answer derived from the comparison between KIVA predictions and experiments that showed a fair agreement between the computed turbulent length scale and the measured lateral integral length scale. The agreement is a result of proper choice of the initial swirl ratio and turbulent kinetic energy at inlet valve closure (IVC) by taking into account the LDV measurements and the value of the constant Cμε in the k-ε model equations that relates the turbulent length scale to k and ε.

In-cylinder cycle-resolved LDV measurements have been made in a diesel engine having a high-squish re-entrant combustion chamber with compression ratio of 21:1. The engine has been motored in the range of 1000 to 3000 rpm thanks to the use of self-lubricating seeding particles. Conventional ensemble-averaging and filtering techniques have been used for analyzing instantaneous velocity data obtained at two points along a diameter located in a horizontal plane at 5 mm below the engine head. The dependence of the mean motion and turbulence on engine speed has been evaluated. The effect of cut-off frequency selection on turbulence values has been also analyzed. Moreover, the Kolmogorov's -5/3 power domain has been investigated in detail by spectral analysis on the instantaneous velocity data.

The characterization of a turbulent diesel spray combustion process has been carried out in a divided chamber diesel system with optical accesses. Laser Doppler Anemometry, spectral extinction and flame intensity measurements have been performed from U.V., to visible from the start of injection to the end of combustion, at fixed air/fuel ratio and different engine speeds. Spatial distribution of fuel and vapor as well as the ignition location and soot distribution have been derived in order to study the mechanism of the air-fuel interaction and the combustion process. The analysis of results has shown that the high swirling motion transports the fuel towards the left part of the chamber and breaks up the jet into small droplets of different sizes and accelerates the fuel vaporization. Then, chemical and physical overlapped phases were observed during the ignition delay, contributing both to autoignition.