A new concept, Diesel Staggered Premixed Ignition with
Accelerated oxidation (D-SPIA) was developed for lower exhaust
emissions and carbon dioxide (CO₂) and this is based on divided
fuel injection before top dead center (TDC). D-SPIA is a result of
investigating various diesel combustion methods. Although the
D-SPIA is a type of Premixed Charge Compression Ignition (PCCI), it
has a distinct feature of double premixed combustion by optimum
injection quantities and staggered timing, which can achieve an
ideal heat release rate for low pollutant emissions and fuel
consumption.
Based on this concept, second injection timing and the
proportion of the second fuel injection quantity play significant
roles to reduce smoke, and hydrocarbon (HC) and carbon monoxide
(CO) emissions. The second injection timing has a close relation to
the premixed time of the second fuel injection and smoke level. The
in-cylinder temperature at the second injection timing, which is
related to the premixed time of the second fuel injection, is
affected by the low-temperature heat release (LTHR) or the
high-temperature heat release (HTHR) of the first fuel injection.
The premixed time of the second fuel injection is required to be
longer with the increase in the second fuel injection quantity. In
addition, the second injection timing and quantity affect the
in-cylinder temperature during the latter phase of the combustion,
which is involved with the oxidation of HC and CO. As the results
of optimizing the D-SPIA combustion, we clarify that our new
concept has clear merits of lower emission levels and lower fuel
consumption together with lower combustion noise compared to
another PCCI that we tested.
We investigated the combustion robustness of the D-SPIA for the
intake air temperature, engine coolant temperature and fuel cetane
index as PCCI has weakness to changes for these environmental
conditions including fuel quality. Through these tests, we found
out that the heat release rate of the D-SPIA could be maintained at
the desired crank angle by control of the air-fuel ratio and/or
injection timing based on changes in the environmental conditions.
In addition, stability of the D-SPIA combustion was maintained even
when using a low cetane index fuel. Finally, we tested a prototype
engine using the D-SPIA combustion concept on a transient engine
test bench and verified that it had a potential to meet the Euro6
regulation without any DeNOx after-treatment and without
deteriorating of fuel consumption. Therefore, we can say that the
D-SPIA has a high potential for introduction into the market.