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Mobile sources
Published in Abhishek Tiwary, Jeremy Colls, Air Pollution, 2017
In California in 2000, diesel engines made up around 3% of the vehicle population and travelled 5% of the miles, yet 35% of the vehicle NOx and 56% of the vehicle exhaust PM were attributed to these vehicles. Diesel engines operate under different combustion conditions to those of petrol engines. The leaner mixture and higher thermal efficiency lead to lower exhaust gas temperatures (200–500°C), with highly oxidising conditions which make for low HC/CO emissions. These emissions can be further reduced with a diesel oxidising catalyst (DOC, see Section 3.1.5.3). However, the same oxidising conditions limit the potential for reducing the NO to N2. DOC can also reduce particle emissions by removing SOF, although creation of sulphate particles from SO2 can more than offset this improvement. Turbocharging reduces both NOx and PM emissions by around 30%, more if combined with aftercooling. The big issue with diesel emission control is how to reduce the concentration of NO without increasing that of particles, and vice versa. For example, retarding the fuel injection reduces the peak flame temperature and hence NOx formation. However, it also lowers fuel efficiency, giving higher overall PM emissions. Emission controls can be acceptably cost-effective. For example, the successive legislation enacted in the US to control mobile source emissions, including diesel, cost typically US$ 1500 per tonne of ozone precursors.
Mobile sources
Published in Abhishek Tiwary, Ian Williams, Air Pollution, 2018
Diesel engines operate under different combustion conditions to those of petrol engines. The leaner mixture and higher thermal efficiency lead to lower exhaust gas temperatures (200°C–500°C), with highly oxidising conditions which make for low HC/CO emissions. Therefore, while three-way catalyst has proved to be very effective at controlling emissions from conventional petrol cars (both during the regulatory laboratory tests and real-world measurements), the picture for diesel cars has been very different (Figure 5.18). In the Euro standards, the diesel engines always have higher permitted limits for NOx emissions than petrol cars.
Combustion engines
Published in Mike Tooley, Lloyd Dingle, Engineering Science, 2020
The reciprocating piston engine works on the four-stroke or two-stroke cycle. Here we concentrate on the four-stroke cycle. In the spark ignition petrol engine the power is generated by the fuel/air mixture being drawn into the cylinder during a suction stroke and being ignited by means of a spark towards the end of the compression stroke. In the case of the compression–ignition oil or diesel engine air only is drawn in during the suction stroke and towards the end of the compression stroke diesel fuel is injected. The high temperature of the compressed air induces the ignition of the fuel/air mix.
Thermal barrier coated diesel engine running on biodiesel: a review
Published in International Journal of Sustainable Engineering, 2018
Energy conservation and efficiency have always been the quest of engineers concerned with internal combustion engines. The diesel engine generally offers better fuel economy than its counterpart petrol engine. Even the diesel engine rejects about two-thirds of the heat energy of the fuel, one-third to the coolant and one-third to the exhaust, leaving only about one-third as useful power output. Theoretically, if the heat rejected could be reduced, then the thermal efficiency would be improved, at least up to the limit set by the second law of thermodynamics. Low heat rejection engines aim to do this by reducing the heat lost to the coolant (Domakonda and Puli, 2012; Soltani et al. 2005; Jaichandar and Tamilporai 2003). Thermal barrier coatings (TBCs) in diesel engines lead to advantages including higher power density, fuel efficiency and multi-fuel capacity due to higher combustion chamber temperature (Zhu and Miller, 1999; Ramaswamy et al. 2000). Using TBC can increase engine power by 8%, decrease the specific fuel consumption by 15–20% and increase the exhaust gas temperature (EGT) 200 K (Ahmaniemi et al. 2003).