The future of vehicle propulsion – combustion engines and alternatives

Topics in Catalysis - Increasing shortage on energy resources as well as future emission legislation development increase the pressure to develop more efficient, environmentally friendly propulsion...     

Traffic-related NO2 and the prevalence of asthma and respiratory symptoms in seven year olds

The aim of this study was to determine whether outdoor nitrogen dioxide (NO2) was associated with the prevalence of asthma and respiratory symptoms. In eight nonurban communities, 843 children resident for a minimum of 2 yrs were studied. Since industrial sources of air pollution were at least 20 km away from the study communities, NO2 was considered to primarily indicate traffic-related air pollution. NO2 was recorded at central monitors, and the 3 yr mean exposure was calculated. Asthma and respiratory symptoms were assessed according to the International Study on Asthma and Allergy in Childhood. Prevalence of asthma at some time ("ever asthma") was associated with long-term NO2. In parallel with increasing levels of NO2 (community specific 3 yr mean 6.0-17.0 parts per billion (ppb)), asthma prevalence was 2.5, 1.4, 1.6, 2.3, 3.4, 3.6, 7.6 and 8.5%, respectively (p=0.002 for trend). The prevalence odds ratios (PORs) for "ever asthma", following adjustment for gender, age, parental education, passive smoke exposure, type of indoor heating, and parental asthma, were 1.28 (95% confidence interval (95% CI) 0.20-7.98), 2.14 (95% CI 0.40-11.3) and 5.81 (95% CI 1.27-26.5), when each of two communities with low, regular and high NO2, respectively, were compared with the two communities with very low NO2. For symptoms "wheeze" (adjusted PORs for increased NO2: 1.47, 1.23 and 2.27) and "cough apart from colds" (adjusted PORs for increased NO2: 1.49, 1.93 and 2.07), a similar trend was seen. In this study a significant relationship was observed between traffic-related nitrogen dioxide and the prevalence of asthma and symptoms. Whether this association is causal has to be tested in longitudinal studies.     

Simultaneous high-speed visualization of soot luminosity and OH1 chemiluminescence of alternative-fuel combustion in a HSDI diesel engine under realistic operating conditions

Crude-oil independent liquid fuels are currently being developed for future HSDI diesel engines. Thus, it is the primary objective of the present study to characterize the combustion of selected reference fuels under realistic conditions, in particular with regard to flame lift-off and soot formation. The experiments are conducted in an optically-accessible and a comparable all-metal HSDI engine at part load, using n-decane, n-heptane, 1-decanol, and conventional diesel, respectively, as the fuel. Two image-intensified, high-speed CMOS cameras are employed simultaneously, in order to visualize the highly unsteady combustion process in terms of OH¹ radicals and soot, respectively, with relatively high temporal resolution and data throughput.The results demonstrate the influence of the fuel properties, in particular cetane number and volatility, on mixture formation, ignition, combustion, soot formation, and emissions. Relatively high soot emissions for n-decane can basically be explained by its short ignition delay, small lift-off length, and lack of fuel-bound oxygen. The soot formation process seems to be more important for the relative engine-out emissions than soot oxidation under the investigated conditions. Furthermore, a very strong correlation between the ignition delay and the flame lift-off length (during injection) is found. This indicates that lift-off stabilization is essentially determined by autoignition.     

Development and design of experiments optimization of a high temperature proton exchange membrane fuel cell auxiliary power unit with onboard fuel processor

In this work, the concept development, system layout, component simulation and the overall DOE system optimization of a HT-PEM fuel cell APU with a net electric power output of 4.5 kW and an onboard methane fuel processor are presented.A highly integrated system layout has been developed that enables fast startup within 7.5 min, a closed system water balance and high fuel processor efficiencies of up to 85% due to the recuperation of the anode offgas burner heat. The integration of the system battery into the load management enhances the transient electric performance and the maximum electric power output of the APU system.Simulation models of the carbon monoxide influence on HT-PEM cell voltage, the concentration and temperature profiles within the autothermal reformer (ATR) and the CO conversion rates within the watergas shift stages (WGSs) have been developed. They enable the optimization of the CO concentration in the anode gas of the fuel cell in order to achieve maximum system efficiencies and an optimized dimensioning of the ATR and WGS reactors.Furthermore a DOE optimization of the global system parameters cathode stoichiometry, anode stoichiometry, air/fuel ratio and steam/carbon ratio of the fuel processing system has been performed in order to achieve maximum system efficiencies for all system operating points under given boundary conditions.     

The Future of Vehicle Propulsion – Combustion Engines and Alternatives

Increasing shortage on energy resources as well as future emission legislation development increase the pressure to develop more efficient, environmentally friendly propulsion systems for vehicles. This requires a further development of current diesel and gasoline engines as well as a careful look to alternatives like fuel cell systems or hybrid propulsion systems. This paper gives a survey about the current status and future developments of internal combustion engines (ICE), as well as some alternatives. A special focus will be on the impact on catalyst development which is in the topic of this conference. The ICE will dominate for vehicle propulsion in the next decades, but will undergo further development. In particular the shift to diesel engines and lean, turbocharged SI-engines will require a continuous development of aftertreatment systems, primarily for Particulates and NO _x . From the alternative fuels natural gas will be the first to play a significant role. The fuel cell will probably have the chance to enter the market only as an auxiliary power unit.     

Quantifying the effects of strains on the conductivity and porosity of LiFePO4 based Li-ion composite cathodes using a multi-scale approach

The effects of the lithium concentration-induced and external load-induced strains on the porosity and electrical conductivity of a LiFePO₄ based Li-ion composite cathode are within the focus of this paper. A micro finite element analysis is first performed considering the arrangement and interaction of the particles in a representative volume element (RVE) of a LiFePO₄–PVDF mixture. The aim is to capture the deformation behavior under different levels of local state of charge (SOC) in lithium concentration, and external loads. Subsequently, apparent conductivities and porosities as a function of SOC and apparent macroscopic volumetric strains are extracted. A larger macro-scale cathode sample is then analyzed, using macro finite element simulations and the extracted apparent properties. Estimated representative spatial SOC profiles under different external pressures are supplied as input. It is found that external assembly loads should not have a considerable influence on the electrochemical performance, since the changes in porosity and conductivity are negligible. Nevertheless, lithium concentrations could account for up to 5% alteration in porosity and conductivity. Even though relatively small, such levels could be meaningful in situations of high rate and poor cell heat dissipation, which is typical in electrified vehicles applications. These strain effects could be considered in a rigorous electrochemical–thermal framework by using porosities and conductivities as a function of local Li concentrations and apparent volumetric strains.     

Percolation-tunneling modeling for the study of the electric conductivity in LiFePO4 based Li-ion battery cathodes

In this work a percolation-tunneling based model is developed and used to study the electrical conductivity of LiFePO₄ composite Li-ion battery cathodes. The active and conductive additive particles are explicitly represented using a random hybrid geometric-mechanical packing algorithm, while the inter-particle electric transport is achieved by including electron tunneling effects. The model is adjusted to the experimental data of a PVDF/C composite with different mixing ratios. The performed study aims to capture the variation of the conductivity of the LiFePO₄ cathode with particle sizes, carbon black particles wt.% and carbon coating wt.%. It is found that ultra fine carbon-free nanosized particles (∼50 nm), which are favorable for improved diffusion, would require a relatively high amount of carbon black (15 wt.%) putting at risk the gravimetric capacity of the cell. On the other hand, particles with 1 wt.% continuous carbon coating delivers already sufficient conductivity for all particle sizes without any additives. The further addition of conductive phases is at the risk of redundancy in view of conductivity enhancements. Although continuous carbon coating with loading as low as 1 wt.% is thought to be the most efficient way to achieve electric conductivity, its manufacturability and effect on Li ion diffusion remain to be assessed.