Potential and Limitations of Dual Fuel Operation of High Speed Large Engines

Abstract

The aim of this paper is to identify and investigate the potential and limitations of diesel–gas combustion concepts for high speed large engines operated in gas mode with very small amounts of pilot fuel (<5% diesel fraction). Experimental tests were carried out on a flexible single cylinder research engine (displacement 6.24 dm3) equipped with a common rail system. Various engine configurations and operating parameters were varied and the effects on the combustion process were analyzed. The results presented in this paper include a comparison of the performance of the investigated dual fuel concept to those of a state-of-the-art monofuel gas engine and a state-of-the-art monofuel diesel engine. Evaluation reveals that certain limiting factors exist that prevent the dual fuel engine from performing as well as the superior gas engine. At the same NOx level of 1.3 g/kWh, the efficiency of the dual fuel engine is ≈3.5% pts. lower than that of the gas engine. This is caused by the weaker ignition performance of the injected pilot fuel compared to that of the gas scavenged prechamber of the gas engine. On the other hand, the dual fuel concept has the potential to compete with the diesel engine. The dual fuel engine can be operated at the efficiency level of the diesel engine yet with significantly lower NOx emissions (3.5 g/kWh and 6.3 g/kWh, respectively). Since the injection of pilot fuel is of major importance for flame initialization, and thus for the main combustion event of the dual fuel engine, optical investigations in a spray box, measurements of injection rates, and three-dimensional (3D) computational fluid dynamics (CFD) simulation were conducted to obtain even more detailed insight into these processes. A study on the influence of the diesel fraction shows that diminishing the diesel fraction from 3% to lower values has a significant impact on engine performance because of the effects of such a reduction on injection, ignition delay, and initial flame formation. The presented results illustrate which operating strategy is beneficial for engine performance in terms of low NOx emissions and high efficiency. Moreover, potential measures can be derived which allow for further optimization of the diesel–gas combustion process.

Methane slip from gas fuelled ships: a comprehensive summary based on measurement data

“…Pilot injections with 1-2 % of full load fuel consumption is achievable, but is rather challenging for stable control. One of the most promising solution is installation of a separate pilot fuel nozzle (either integrated in one housing or installed as a separate fuel injector) [42,43,44]. Pilot fuel can be either injected directly into the (main) combustion chamber or in a pre-chamber.…”

Tabulated Chemistry Combustion Model for Cost-Effective Numerical Simulation of Dual-Fuel Combustion Process

“…This type of engine is operated by burning a premixed natural gas/air mixture ignited with a small amount of directly injected diesel fuel. This concept has several disadvantages, which are discussed in [5]. Nevertheless, dual-fuel engines are the subject of active research, and establishing an effective design process for dual-fuel engines and its fuel injection equipment represents a key priority.…”

A Computational Investigation of the Impact of Multiple Injection Strategies on Combustion Efficiency in Diesel–Natural Gas Dual-Fuel Low-Temperature Combustion Engines

“…Recent developments in advanced combustion concepts have focused on using two fuels of different propensities to autoignition to achieve high FCEs and ultra low NO x emissions [6][7][8]. These combustion concepts introduce a low reactivity fuel (e.g., natural gas or gasoline) through the intake manifold to create a premixed charge, which is compression-ignited using a high-pressure, high reactivity fuel spray (e.g., diesel) [9,10].…”

“…These dual-fuel lowtemperature combustion (LTC) concepts, using natural gas, have immense potential to reduce CO 2 emissions; however, there is the added risk of "methane slip," i.e., any amount of unburned natural gas that escapes the tailpipe posing a risk. For example, if the engine-out methane emissions are greater than 0.1 g/bhp h, then they must be multiplied by a global warming potential factor of 34 [7]. A particular scenario of concern occurs at low engine loads where the coauthors and other researchers have observed instances of high engine-out unburned hydrocarbon (UHC) and carbon monoxide (CO) emissions and high cyclic combustion variations [10][11][12].…”