Experimental Studies of Low-Load Limit in a Stoichiometric Micro-Pilot Diesel Natural Gas Engine

Vinicius Bonfochi Vinhaes,Sandeep Munshi,Jeffrey D Naber,Mahdi Shahbakhti,Gordon Mctaggart-Cowan

doi:10.3390/en15030728

Vinicius Bonfochi Vinhaes, Sandeep Munshi + Show 3 more

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https://doi.org/10.3390/en15030728

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Abstract

While operating at light loads, diesel pilot-ignited natural gas engines with lean premixed natural gas suffer from poor combustion efficiency and high methane emissions. This work investigates the limits of low-load operation for a micro-pilot diesel natural gas engine that uses a stoichiometric mixture to enable methane and nitrogen oxide emission control. By optimizing engine hardware, operating conditions, and injection strategies, this study focused on defining the lowest achievable load while maintaining a stoichiometric equivalence ratio and with acceptable combustion stability. A multi-cylinder diesel 6.7 L engine was converted to run natural gas premix with a maximum diesel micro-pilot contribution of 10%. With a base diesel compression ratio of 17.3:1, the intake manifold pressure limit was 80 kPa(absolute). At a reduced compression ratio of 15:1, this limit increased to 85 kPa, raising the minimum stable load. Retarding the combustion phasing, typically used in spark-ignition engines to achieve lower loads, was also tested but found to be limited by degraded diesel ignition at later timings. Reducing the pilot injection pressure improved combustion stability, as did increasing pilot quantity at the cost of lower substitution ratios. The lean operation further reduced load but increased NOx and hydrocarbon emissions. At loads below the practical dual-fuel limit, a transition to lean diesel operation will likely be required with corresponding implications for the aftertreatment system.

Highlights

Publisher’s Note: MDPI stays neutralModern society relies on the transportation of products and people, and due to the abundant supply, convenience, and affordability of liquid fuels, transportation is virtually entirely powered by conventional internal combustion engines (ICEs)
This work focused on studying the limits of the low-load operation of a micro-pilot diesel natural gas engine and the effect of controlling parameters including engine hardware by reducing compression ratio and finding the optimum operating condition by sweeping the diesel pilot start of injection and dilution with cooled exhaust gas recirculation (EGR), as well as adjusting the pilot injection strategy by sweeping injection pressure and injection quantity
These factors were independently investigated with the goal of reaching the minimum load limit while being constrained by the need to operate at stoichiometric equivalence ratio, minimum intake manifold pressure, and having stable combustion

Summary

Introduction

Publisher’s Note: MDPI stays neutralModern society relies on the transportation of products and people, and due to the abundant supply, convenience, and affordability of liquid fuels, transportation is virtually entirely powered by conventional internal combustion engines (ICEs). Demand for high-efficiency engines with high specific power output, low greenhouse gas emissions, and ever lower pollutant emissions is expected to continue to grow [2]. Natural gas (NG) as an alternative fuel is an exciting subject of research in ICEs because of its significant potential to reduce CO2 and oxides of nitrogen (NOx) emissions [3]. Compression ignition engine types that burn two distinct fuels in different mixture quantities simultaneously are often described as dual-fuel engines. The combination of the lean-burn of a premixed NG–air mixture with a considerable quantity of diesel injection as the combustion pilot is a characteristic of the conventional dual-fuel engines [4]. Diesel-like fuel conversion efficiencies and relatively low NOx emissions have been demonstrated in with regard to jurisdictional claims in published maps and institutional affiliations

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