Konstantinos Boulouchos

An amendment to this paper has been published and can be accessed via the original article.

Cars have a high share of global transport-related CO₂ emissions. To model the market diffusion of new energy carriers and powertrains like electric vehicles, fleet turnover models are commonly used. A decisive influence factor for the substitution dynamics of such transformations is the survival rate of the national car fleet of a country. It represents the likelihood of a car reaching a certain lifespan. Due to a lack of data, current methods to estimate such survival probabilities neglect the imports and exports of used cars. Existing studies are limited to countries with a predominant market of new cars, compared to low numbers of imported and exported used cars. In this study, we resolve this marked simplification and propose a new method to estimate survival probabilities for countries with a high number of imported and exported used cars. Empirical data on the car stock, on inflows of new and used cars, and on outflows of exported and scrapped cars are gathered from 71 national statistics offices. Survival rates of the car fleets of 31 European countries are derived, for which we find a pronounced regional variability. Average lifespans of cars vary from 8.0 to 35.1 years, with a mean of 18.1 years in Western and 28.4 years in Eastern European countries, revealing the high impact of cross-border flows of cars. The study also shows that survival rate estimates can be improved significantly even in the absence of reliable data if a combination of a Weibull and a Gaussian distribution is used. It is likely that the predictive power of existing models (regarding the future environmental impact of car fleets) could be improved significantly if these findings were considered accordingly. The findings of this study can directly be included in fleet turnover and policy assessment models. They also enable the analysis of economic and environmental spillover effects from the imports and exports of used cars between countries.

Decentralized power generation by combined heat and power plants becomes increasingly popular as a measure to advance the energy transition. In this context, a substantial advantage of small combined heat and power plants is based on the relatively low pollutant emissions. However, a large proportion of the pollutant emissions is produced during a cold-start. This fact is not reflected in governmental and institutional emission guidelines, as these strongly focus on the emission levels under steady-state conditions. This study analyzes the spark advance, the reference air/fuel ratio and an electrically heated catalyst in terms of their potential to reduce the cold-start emissions of a micro combined heat and power plant which uses a natural gas fueled reciprocating internal combustion engine as prime mover and a three-way catalytic converter as aftertreatment system. Based on these measures, control approaches were developed that account for the specific operating conditions of the class of small combined heat and power plants, e.g., full-load operation and flexible, demand-driven runtimes. The experimental data demonstrates that even solutions with marginal adaptation/integration effort can reduce cold-start emissions to a great extent.

A new test rig has been designed, built and commissioned, and is now jointly pursued to facilitate experimental investigations into advanced combustion processes (i.e., dual fuel, multi-mode) under turbulent conditions at high, engine-like temperature and pressure levels. Based on a standard diesel engine block, it offers much improved optical access to the in-cylinder processes due to its separated and rotated arrangement of the compression volume and combustion chamber, respectively. A fully variable pneumatic valve train and the appropriate preconditioning of the intake air allows it to represent a wide range of engine-like in-cylinder conditions regarding pressures, temperatures and turbulence levels. The modular design of the test rig facilitates easy optimizations of the combustion chamber/cylinder head design regarding different experimental requirements. The name of the new test rig, Flex-OeCoS, denotes its Flexibility regarding Optical engine Combustion diagnostics and/or the development of corresponding Sensing devices and applications. Measurements regarding in-cylinder gas pressures, temperatures and the flow field under typical operating conditions are presented to complete the description and assessment of the new test rig.

State of the art high-pressure fuel injectors offer the ability to inject multiple times per cycle, and can reach very low fuel amounts per injection event. This behaviour allows the application of pilot injections in diesel engine applications or dual fuel engines. In both diesel and dual fuel engines, the amount of pilot fuel affects the engine efficiency. The understanding of the underlying ignition mechanism of the pilot fuel is required to optimize injection parameters and the engines’ fuel consumption.The present work focuses on the differences of ignition mechanisms between long and short injections. The investigation has been performed numerically, using CFD with a well-proven combustion model. The setup used employs a well characterized single orifice injector, injecting into a high temperature, pressurized environment with a composition of 15% oxygen. The duration of injection (DOI) has been gradually decreased form 1.5 ms to 0.3 ms, while a square mass flow rate profile has been employed.The analysis distinguishes between long, medium and short DOIs: the reference ignition delay is defined by the long DOIs, for which constant ignition delays are found. Shortening the injection duration leads to a decrease in ignition delay for medium DOIs (accelerated case), while for short DOIs an ignition delay trend reversal is observed (prolonged case). The ignition location is close to the spray tip for the long and the short cases, while it moves towards the spray tail for the medium DOIs. The ignition delays of the medium DOIs are shorter due to enhanced mixing after end of injection. The relatively larger areas of leaner mixture increase the temperature and in particular the contribution of the low temperature reactions, which promotes ignition. In the short DOIs, the ignition delay is longer due to overmixing, which reduces the mixture reactivity and prolongs the ignition delay. The ignition moves towards the most fuel rich location in the spray, which lies close to the spray tip at a certain time after the end of injection.

In the present work, numerical simulations are carried out to investigate underexpanded methane jets with phase separation effects. In order to predict the fuel injection and the mixture formation in the constant volume chamber, a hybrid, pressure-based solver is combined with a vapor-liquid equilibrium model and a moving mesh methodology. The thermodynamic models are based on the cubic equation of state of Soave, Redlich, and Kwong. A compressibility correction for the widely known kωSST turbulence model is implemented additionally. Application-relevant simulations with a total fuel pressure of 300 bars and five different chamber pressures ranging from 12 to 60 bars were defined. Furthermore, the influence of two fuel and chamber temperatures, 294 and 363 K, is analyzed. Depending on the chamber pressure, two different flow structures of the potential core can be distinguished: (1) A series of typical shock barrels for small pressure ratios and moderately underexpanded jets and (2) a shear layer consisting of a two-phase mixture which enfolds the potential core for high pressure ratios and highly underexpanded jets. Increasing the fuel temperature leads to less significant phase separations, while an increase in the chamber pressure does not affect the structure of the potential core. A comparison with experimental measurements shows a very good agreement of the simulated structure of the potential core, providing evidence that the underlying phenomena are predicted correctly and suggesting that a moving mesh strategy and consistent two-phase thermodynamics implementation are necessary for a physical representation of high-pressure injections.