Andrea Unich

A Review of Hydrogen-Natural Gas Blend Fuels in Internal Combustion Engines

In the last ten years, the number of natural gas (NG) vehicles worldwide has rapidly grown with the biggest contribution coming from the Asia-Pacific and Latin America regions (IANGV, 2011). As natural gas is the cleanest fossil fuel, the exhaust emissions from natural gas spark ignition vehicles are lower than those of gasoline-powered vehicles. Moreover, natural gas is less affected by price fluctuations and its reserves are more evenly widespread over the globe than oil. In order to increase the efficiency of natural gas engines and to stimulate hydrogen technology and market, hydrogen can be added to natural gas, obtaining Hydrogen Natural Gas blends, usually named as HCNG.

Numerical Modelling of Internal Combustion Engines Fuelled by Hydrogen-Natural Gas Blends

The strict rules that European Community has given for reducing vehicle emissions require new views on the choice of combustion engines and fuels. In fact, the rules will probably introduce in the near future limitations on carbon dioxide (CO2 ) emissions. Internal combustion engines are responsible for emission of unburned hydrocarbons (HC), nitrogen oxides (NOx) and particulate matter (PM). The aim of the present paper is the study of the effects of hydrogen-natural gas blends (HCNG) on the performance, efficiency and NOx emissions of internal combustion engines (ICE). A numerical engine model has been developed to display how the presence of hydrogen in such mixtures impacts on flame speed and burn rates. The model allows the comparison of different fuels, in terms of engine brake efficiency and pollutant emissions. An important variable for the combustion process is the ignition timing which is set employing Maximum Brake Torque (MBT) spark advance. Engine operating conditions considered in the numerical analysis have been obtained by imposing engine speed and load. Brake power, efficiency and NOx emissions are calculated for the most frequent operating conditions met by automotive engines, i.e. part load and low speed. The effect of natural gas (NG) enrichment by hydrogen on flame speed has been considered. Thus, faster combustion and the reduction of energy content in the air-fuel mixtures due to the lower density of hydrogen are taken into account. Hydrogen enrichment of natural gas improves combustion stability in critical conditions, allowing the use of extremely lean mixtures or high Exhaust Gas Recirculation rates. The results show that by employing an MBT spark advance, the HCNG blends furnish improvements of engine brake efficiency compared with compressed natural gas (CNG), which are more relevant at part loads and for the higher hydrogen content. Anyway, higher NOx emissions are observed due to the increased temperatures into the cylinders. Thus, the analysis also takes into account the Exhaust Gas Recirculation (EGR) dilution technique to reduce the NOx emissions. A large reduction of such pollutant, which has been estimated greater than 50%, can be achieved by using a 10% EGR. Furthermore higher engine efficiency is obtained using EGR due to reduced pumping work, reduced heat loss to the walls because of lower gas temperature and a reduction in the degree of dissociation in the high temperature burned gases.Copyright

The Effect of Humidification Strategies on Efficiency and Durability of Hydrogen Fuel Cells in Automotive Application

In this paper the effect of different humidification strategies on performance of fuel cell systems (FCS) based on proton exchange membrane (PEM) fuel cells was analyzed taking into account the specific requirements of an automotive application. The experiments were conducted on PEM fuel cell systems of different power, ranging from 2.4 to 14 kW. The results showed that the optimal humidification strategy was function of stack operation mode and energy management inside the overall system, and evidenced the benefits and limitations of the self-humidification strategy for an automotive application.