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Ultrafine particles, in particular solid sub-100 nm particles pose high risks to human health due to their high lung deposition efficiency, translocation to all organs including the brain and their harmful chemical composition; due to dense traffic, the population in urban environments is exposed to high concentrations of those toxic air contaminants, despite these facts, they are still widely neglected. Therefore, the EU-Commission set up a program for clean and competitive solutions for different problem areas which are regarded to be hotspots of such particles. HORIZON AeroSolfd is an EU project, co-funded by Switzerland that will deliver affordable, adaptable, and sustainable retrofit solutions to reduce exhaust tailpipe emissions from petrol engines, brake emissions and pollution in semi-closed environments.

Concern for engine particle emission led to EC regulations of the number of solid particles emitted by LDV and HDV. However, all conventional piston-driven combustion engines emit metal oxide particles of which only little is known. The main sources are abrasion between piston ring and cylinder, abrasion of bearing, cams and valves, catalyst coatings, metal-organic lubrication oil additives, and fuel additives. While abrasion usually generates particles in the μm range, high concentrations of nanosize metal oxide particles are also observed, probably resulting from nucleation processes during combustion. In general, metal oxides, especially from transition metals, have high surface reactivity and can therefore be very toxic, especially nanosize particles, which evidently provide a high specific bioactive surface and are suspected to penetrate into the organism. Hence, these particles must be scrutinized for quantity, size distribution and composition.

It is possible to have a clean green diesel engine with low exhaust emissions and excellent fuel economy. The two major requirements for this engine are a low sulfur diesel fuel to permit the application of emission controls, and the support of effective regulations and standards. The diesel engine is a major contributor to air pollution - especially within cities and along urban traffic routes. Because diesel engines are extremely durable - lasting for 20 to 40 years, once they are introduced in an area they contribute to the air pollution problems for decades. Off-road vehicles further contribute to the pollution problem. Consequently, India needs to devise an emission control strategy that addresses both new and old engines. In addition to the normal components of air pollution that cause ground level ozone and smog in the atmosphere, diesel exhaust also contains particulate and hydrocarbon toxic air contaminants (TAC). These pollutants pose additional human health concerns.

Environmental concerns and regulations have stimulated the study of applying catalytic emission control to 4-stroke air cooled utility engines of less than 25 Hp. These engines require air/fuel mixtures considerably richer than those of automotive engines, entailing different catalytic solutions. In addition, small utility engines are subjected to a variety of unique operating modes. Factors discussed for this new catalyst system application are space velocity, temperature, test cycle, operating modes, lube oil consumption, engine control systems, engine life, and operating efficiency as well as other factors unique to this engine. An unexpected effect of this catalyst application, after-ignition of unburned exhaust components in a classical diffusion flame, is also discussed. It appears that catalytic emission control of small 4-stroke utility engines can be effective.

The performance of platinum/rhodium based TWC catalysts was compared to that of palladium/rhodium based TWC catalysts for the control of emissions from an M-85 fueled vehicle. The catalysts were artificially aged on an engine test stand using a simulated fuel cut aging cycle. The evaluation test cycle was the US FTP-75 test. A REGA 7000 FTIR system was used to specifically monitor methanol and formaldehyde emissions. Double layered palladium/rhodium based TWC catalysts exhibited better methanol and formaldehyde removal as well as superior overall performance. Essentially all of the hydrocarbon emission occurred during cold start. It was demonstrated that significant reduction in formaldehyde and methanol emission could be achieved by presenting a hotter exhaust gas to the converter by use of a small starter catalyst located near the engine.

In the effort to design reliable diesel engines which meet the strict US Federal Regulations for emissions, considerable progress has been made by engine manufacturers. Particulate emissions are now below 0.25 g/BHPh and after 1994 will be below 0.1 g/BHPh. Diesel fuel has a revised specification limit of 0.05% sulfur as a means to assist diesel engine manufacturers in complying with the 1994 standard. Diesel oxidation catalysts (DOC) have been chosen as another means. A DOC can efficiently oxidize soluble organic particulate matter (SOF) and gaseous hydrocarbons while easily oxidizing SO2 to SO3-the latter being a particulate and undesirable. Selective DOCs have been developed which maintain the activity for SOF and minimize the undesirable SO2 oxidation step. However, performance for gaseous hydrocarbons may be negatively affected.