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Phone: +34 963877650 Fax: +34 963877659 e-mail: vidolrui@mot.upv.es 1 all the parameters, changing each time one specific value. In these sensitivity studies, maximum ideal and real Rankine efficiency value of 19% and 6% were obtained respectively.

This paper deals with the evaluation and analysis of a bottoming ORC cycle coupled to an IC engine by means of conventional and advanced exergy analysis. Using experimental data of an ORC coupled to a 2 l turbocharged engine, both conventional and advanced exergy analysis are carried out. Splitting the exergy in the advanced exergy analysis into unavoidable and avoidable provides a measure of the potential of improving the efficiency of this component. On the other hand, splitting the exergy into endogenous and exogenous provides information between interactions among system components. The result of this study shows that there is a high potential of improvement in this type of cycles. Although, from the conventional analysis, the exergy destruction rate of boiler is greater than the one of the expander, condenser and pump, the advanced exergy analysis suggests that the first priority of improvement should be given to the expander, followed by the pump, the condenser and the boiler. A total amount of 3.75 kW (36.5%) of exergy destruction rate could be lowered, taking account that only the avoidable part of the exergy destruction rate can be reduced.

Injection rate shaping is one of the most attractive alternatives to multiple injection strategies; however, its implementation has been for long time impeded by limitations in the injector technology and therefore, the experimental information available in the literature about this topic is lacking.In this work, a novel prototype common-rail injector featuring direct control of the nozzle needle by means of a piezo-stack (direct-acting) allowed a fully flexible control on the nozzle needle movement and enabled the implementation of alternative injection rate shapes typologies. This state of the art injector, fitted with a 7-hole nozzle, was tested at real engine conditions studying the spatial-temporal evolution of CH* and OH* chemiluminescence intensity produced by the fuel combustion. A wide test matrix was performed in an optically accessible hot-spray test rig to understand the influence that partial needle lift and alternative injection rate shapes have on the Diesel ignitionThe results showed that alternative injection rate profiles have a substantial impact on the ignition event affecting the premixed phase of the combustion and the location where the ignition takes place. Moreover, the results proved that the modifications in the internal flow caused by the partial needle lift are reflected on the ignition timing: although partial needle lift and injection pressure have similar effects on the mass flow rate, in the first case the ignition delay is reduced, while in the second the combustion is delayed as a consequence of a different spray development. IntroductionFuel-air mixing process, combustion and emission phenomena are necessarily linked together in direct injection Diesel engines [1][2][3][4][5]. In a scenario where the global emission standards require higher engine performances in terms of combustion efficiency and emissions reduction, all the efforts by the engine community to improve the understanding of the fuel atomization, spray development and combustion are largely justified.Over the past decades, many studies have been carried out to develop a better understanding of the mixing process [6][7][8] and of the fuel ignition [9][10][11][12]. Experimental facilities, such as optically accessible engines [13] and test rig cells [11,14] combined with imaging techniques [5,15], have become the most common tools used in spray research. Throughout the years, the efforts put in place in these studies generated an accurate and deep understanding of the injection combustion event in Diesel engines.On the other hand, several activities have been performed to advance the flexibility of the fuel injection system, achieving significant improvements [2]. Most of these systems are operated with electro-hydraulic actuation, where the fuel injector is activated using either a solenoid or a piezo-stack; however, the opening of the injector itself is produced by the pressure difference at the two sides of the needle limiting the injection control to an on-off mode. As a consequence of that, multiple in...

It is widely acknowledged that the development of sprays in the near-field is of primary importance for the spray formation downstream, as it affects both the spray angle, as well as the intact core length. In this frame, the present work aims to study the effects of turbulence inlet boundary condition on the spray formation by means of Direct Numerical Simulations on a real condition at low Reynolds number. To this extent, the code Paris-Simulator has been used, while a digital filter-based algorithm was used in order to generate synthetic turbulence at the inlet boundary condition. The influence of turbulence intensity and lengthscale on the atomization process has been studied and analyzed through 3 simulation for which these parameters have been varied. The results clearly highlight how the atomization is heavily affected by the inlet turbulence configuration. An analysis of the different atomizing conditions has been conducted, aiming to understand how the variation introduced by the inlet boundary condition on the velocity field is affecting the local atomization dynamics.

The effect of low ambient temperature on diesel raw pollutant emissions is analysed in two different driving cycles: NEDC and WLTC. The study is focused on hydrocarbons, carbon monoxide, nitrogen oxides and fuel consumption. Tests are conducted at cold start in a HSDI light-duty diesel engine with two levels of ambient temperature: 20 °C and −7 °C. Results showed a general detriment of pollutant emissions and break thermal efficiency at low ambient temperatures. NOx is increased around 250% in both cycles when running at low temperatures. Effect on hydrocarbons is more noticeable in the NEDC, where it rises in 270%, compared with the 150% of increase in the WLTC. In the case of carbon monoxide, uncorrelated tendencies are observed between both driving cycles. Concerning the NEDC, carbon monoxide emissions increase up to 125%, while at the WLTC, they are reduced up to 20%. Finally, from the point of view of the thermal efficiency, a reduction of nearly 10% in the NEDC is observed. However, no fuel penalty is spotted regarding the WLTC.

Low viscosity engine oils (LVO) are considered key contributor for improving fuel economy in internal combustion engines (ICE). Attending that the use of LVO could imply a variation in tribological states found in ICE, this work's aim is to test LVO in real fleet, with emphasis on engine wear and oil key performance indicators. This test comprised 39 buses, two engine technologies and four different lubricants. For each sample, the elemental composition of the wear debris by ICP-AES and HTHS viscosity of the oil were measured among other properties. The results showed that, with a correct oil formulation, there is no significant difference when using LVO in terms of engine wear, HTHS viscosity variation and oil consumption.

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