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The internal flow in an injector is greatly affected by cavitation formation, and this in turn impacts the spray characteristics of diesel injectors. In the current work, the performance of the Homogeneous Relaxation Model (HRM) in simulating cavitation inside a diesel injector is evaluated. This model is based on the assumption of homogeneous flow, and was originally developed for flash boiling simulations. However, the model can potentially simulate the spectrum of vaporization mechanisms ranging from cavitation to flash boiling through the use of an empirical time scale which depends on the thermodynamic conditions of the injector fuel. A lower value of this time scale represents a lower deviation from thermal equilibrium conditions, which is an acceptable assumption for small-scale cavitating flows. Another important advantage is the ability of this model to be easily coupled with real fuel models.

Regulations on emissions from diesel engines are becoming more stringent worldwide. Hence there is a great deal of interest in developing engine combustion systems that offer the fuel efficiency of a diesel engine, but with low smoke and NOx emissions. Thus, premixed compression ignition combustion is an interesting way to achieve a clean and efficient engine. However, using a high reactivity fuel such as diesel fuel leads to a complex and expensive engine design. A proven way to overcome this drawback is to actively control the reactivity of the fuel using low cetane fuels such as gasoline. This strategy has been explored with single and multiple cylinder engines. However no detailed and well conducted studies of the injection process were found related to the effects of gasoline use in a standard commercial compression ignition diesel engine injection system.

An investigation of high speed direct injection (DI) compression ignition (CI) engine combustion fueled with gasoline (termed GDICI for Gasoline Direct-Injection Compression Ignition) in the low temperature combustion (LTC) regime is presented. As an aid to plan engine experiments at full load (16 bar IMEP, 2500 rev/min), exploration of operating conditions was first performed numerically employing a multi-dimensional CFD code, KIVA-ERC-Chemkin, that features improved sub-models and the Chemkin library. The oxidation chemistry of the fuel was calculated using a reduced mechanism for primary reference fuel combustion. Operation ranges of a light-duty diesel engine operating with GDICI combustion with constraints of combustion efficiency, noise level (pressure rise rate) and emissions were identified as functions of injection timings, exhaust gas recirculation rate and the fuel split ratio of double-pulse injections.