Javier Monsalve-Serrano

Impact of Spark Assistance and Multiple Injections on Gasoline PPC Light Load

Along the last years, engine researchers are more and more focusing their efforts on the advanced low temperature combustion (LTC) concepts with the aim of achieving the stringent limits of the current emission legislations. In this regard, several studies based on highly premixed combustion concepts such as HCCI has been confirmed as a promising way to decrease drastically the most relevant CI diesel engineout emissions, NOx and soot. However, the major HCCI drawbacks are the narrow load range, bounded by either misfiring (low load, low speed) or hardware limitations (higher load, higher speeds) and the combustion control (cycle-tocylce control and combustion phasing). Although several techniques have been widely investigated in order to overcome these drawbacks, the high chemical reactivity of the diesel fuel remains as the main limitation for the combustion control. The attempts of the researchers to overcome these disadvantages are shifting to the use of fuels with different reactivity. In this sense, gasoline PPC has been able to reduce emissions and improve efficiency simultaneously, but some drawbacks regarding controllability and stability at low load operating conditions still need solution. In this field, previous researches have been demonstrate the multiple injection strategy as an appropriate technique to enhance the combustion stability. However, PPC combustion has been found limited to engine loads higher than 5 bar BMEP when using fuels with octane number greater than 90. In this regard, previous work from the authors showed the capability of the spark plug to provide combustion control in engine loads below this limit even using 98 ON gasoline. The main objective of the present work is to couple the control capability of the spark assistance together with an appropriate mixture distribution by using double injection strategies with the aim of evaluating performance and engine-out emissions at low load PPC range using a high octane number gasoline. For this purpose the optical and metal version of a compression ignition single-cylinder engine, to allow high compression ratio, has been used during the research. A common rail injection system enabling high injection pressures has been utilized to supply the 98 octane number gasoline. An analysis of the incylinder pressure signal derived parameters, hydroxyl radical (OH*) and natural luminosity images acquired from the transparent engine as well as a detailed analysis of the air/fuel mixing process by means of a 1-D in-house developed spray model (DICOM) has been conducted. Results from both analysis methods, suggest the spark assistance as a proper technique to improve the spatial and temporal control over the low load gasoline PPC combustion process. A noticeable increase in the cycle to cycle repeatability (5% versus 15.1% CoV IMEP at 2 bar load) as well as a reduction in the knocking level (20.5 versus 33.6 MW/m at 7 bar load) is observed. In addition, the combination of the spark assistance with the use of the double injection strategy provides a great improvement in terms of combustion efficiency (93% versus 88% for a single injection strategy) with a benefit around 18% in the IMEP.

Evaluating the reactivity controlled compression ignition operating range limits in a high-compression ratio medium-duty diesel engine fueled with biodiesel and ethanol

This work investigates the load limits of reactivity controlled compression ignition combustion, a dual-fuel concept which combines port fuel injection of low-reactivity fuels with direct injection of diesel fuel, in a medium-duty diesel engine. The experiments were conducted in a single-cylinder diesel engine derived from the multi-cylinder production engine. In this sense, the stock turbocharger and exhaust gas recirculation systems were replaced by an external compressor and dedicated low-pressure exhaust gas recirculation loop, respectively. Additionally, a port fuel injector was installed in the intake manifold to allow gasoline injection. First, this article presents some results highlighting the effect of the exhaust gas recirculation rate, gasoline fraction, diesel start of injection, diesel injection strategy and intake temperature on the emissions, performance and combustion development in a representative operating condition: 1200 r/min and 6.5 bar indicated mean effective pressure (25% load). Later, with the aim of showing the reactivity controlled compression ignition potential, the best results in terms of performance and emissions at 25% load are compared against the multi-cylinder diesel engine from 950 to 2200 r/min. Reactivity controlled compression ignition engine tests were developed taking into account limitations in nitrogen oxides (NOx) and soot emissions, in-cylinder pressure and maximum pressure rise rate. Finally, keeping the same constraints for testing, the load limits of reactivity controlled compression ignition concept are evaluated for all the engine speeds. Results suggest that reactivity controlled compression ignition allows fulfilling EURO VI limits for NOx and soot emissions without using selective catalytic reduction and diesel particulate filter aftertreatment systems at 25% load at all the engines speeds, providing better indicated efficiency than conventional diesel operation in most operating points. In addition, the maximum engine load that ensured the aforementioned constraints was around 35% for all the engine speeds, with a maximum indicated mean effective pressure of 8.8 bar at 2200 r/min. In this case, a strong reduction in carbon monoxide (CO) and unburned hydrocarbon (HC) emissions compared to the cases of 25% load was achieved at all the engine speeds.