An Experimental Investigation of Diesel-Gasoline Blends Effects in a Direct-Injection Compression-Ignition Engine Operating in PCCI Conditions 2013-01-1676

Compared to the gasoline engine, the diesel engine has the advantage of being more efficient and hence achieving a reduction of CO₂ levels. Unfortunately, particulate matter (PM) and nitrogen oxides (NO_x) emissions from diesel engines are high. To overcome these drawbacks, several new combustion concepts have been developed, including the PCCI (Premixed Charge Compression Ignition) combustion mode. This strategy allows a simultaneous reduction of NO_x and soot emissions through the reduction of local combustion temperatures and the enhancement of the fuel/air mixing. In spite of PCCI benefits, the concept is characterized by its high combustion noise levels. Currently, a promising way to improve the PCCI disadvantages is being investigated. It is related with the use of low cetane fuels such as gasoline and diesel-gasoline blends.

In this paper an experimental study is carried out focusing on evaluating emissions, performances and combustion noise in PCCI conditions when using diesel-gasoline blends. For this purpose, a parametrical study has been performed varying injection timing and fuel type in a High Speed Direct Injection (HSDI) diesel engine.

Results show how increasing the gasoline percentage in the fuel blend results in an enlarged ignition delay, therefore achieving an extended mixing time between the End of Injection (EoI) and the Start of Combustion (SoC). As a consequence, lower local equivalence ratios are achieved and therefore lower soot emissions are reached. Additionally, performances and the sound quality of combustion noise are improved. By contrast, NO_x levels are slightly increased.