High Efficiency and Clean Diesel Combustion Concept using Double Premixed Combustion: D-SPIA 2012-01-0906

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.