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Cold Start on Diesel Engines: Effect of Fuel Characteristics
Abstract:
Faced with the need to reduce greenhouse gas emissions, diesel
engines present the advantage of having low CO₂ emission levels
compared to spark-ignited engines. Nevertheless, diesel engines
still suffer from the fact that they emit pollutants and,
particularly nitrogen oxides (NOx) and particulates (PM). One of
the most promising ways to meet this challenge is to reduce the
compression ratio (CR). However a current limitation in reducing
the diesel CR is cold start requirements.
In this context, the fuel characteristics such as the cetane
number, which represents ignition, and volatility could impact cold
start. That is why a matrix of 8 fuels was tested. The cetane
number ranges from 47.3 to 70.9 and the volatility, represented by
the temperature necessary to distillate 5% of the product (T5%),
ranges from 173 to 198°C. The engine tests were carried out at
-25°C, on a common rail 4-cylinder diesel engine. Two engine
configurations were studied: a nominal CR of 16:1 and a reduced CR
of 14:1. Operating points were run with the same settings for all
the fuels. Moreover a statistical analysis of the results was used
in order to highlight the fuel impacts on cold behavior (start and
idle).
The main results show that the difference between tests operated
with CR equal to 16:1 and 14:1 appears only during the idle phase.
The impact of volatility is not clear, but the increase in cetane
number means better performances on cold start.