Troels Dyhr Pedersen.indd - Solid Mechanics

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Design changes such as downscaling (both engine and vehicle) or improved
aerodynamics are also logical means of achieving the same fuel saving with even lower
cost to the consumer, assuming that the consumers can accept smaller cars. Reducing the
size of the engine is however often connected with extra costs for pressure charging and
other means of maintaining (or even increasing) the engine power, so the resulting cost
saving from reduced fuel consumption is most likely offset by the higher cost of the
vehicle. Downscaled engines is therefore of limited interest to the consumer.
Given that HCCI is not the only candidate technology for obtaining a better fuel
economy, it must be competitive in cost to the other solutions, as well as offering other
benefits. A good argument for using the HCCI principle is that it can potentially eliminate
the need for expensive after-treatment solutions that are otherwise required to remove
emissions of particulate matter and nitric oxides. The only problematic emissions from
HCCI combustion are unburned hydrocarbons and carbon monoxide. These are however
easily removed by an inexpensive oxidizing catalyst. Such catalysts have a high
conversion factor even at low exhaust temperatures, meaning that HCCI engines can
easily meet current emission requirements.
The direction of future developments based on the HCCI concept is still largely
undetermined. The main reason is the degree of freedom allowed in terms of fuels,
injection principles and controlling strategies, which require a large amount of research to
cover. Each proposed concept has its own benefits and disadvantages, and so far no
concept has made any significant breakthrough that makes large scale production of the
engines possible. It is however likely that HCCI engines will be ready for commercial use
within a few years, simply because increasing fuel costs make such investments both
logical and necessary.
5.2 Background of this project
The use of DME as a diesel substitute had been in focus for some years at Department of
Mechanical Engineering. The first person to demonstrate DME in an engine was Svend
Erik Mikkelsen from Haldor Topsøe A/S, who discovered its potential by using it in a
lawn mover and a fork lift. Despite switching of the ignition the engine continued
running, thereby demonstrating its diesel ignition properties in an engine with a
compression ratio suited for gasoline. These discoveries lead to a project, in which DME
was tested in a small diesel engine at DTU [5]. Results were promising, but it was also
clear that DME did not have the lubricity required to function with standard diesel high
pressure pumps and injectors [6]. A high pressure pump requires a fuel with lubrication,
since the surfaces will otherwise make contact and the pump will therefore eventually
wear out. Diesel injectors are also to some degree susceptible to wear if the fuel does not
have any lubricity.
The troubles with diesel injection equipment lead to the idea of using HCCI combustion
of DME instead, since this would not require high pressure injection systems. The author
was offered this option for his M.Sc. project. The project successfully demonstrated the
concept [7]. Funding for a Ph.D. position was given to continue the research, and the
outcome is described in this thesis.