Gaseous fuels variation effects on first and second law analyses of a small direct injection engine for micro-CHP systems

Significance 

Clean energy activism, stringent policies and laws being developed and adopted by governments globally have driven energy researchers to create more energy efficient systems. A near reflex action has been the increased focus on the readily available alternative energy sources that could offer reduced carbon emissions and at the same time be cost effective. One such alternative is natural gas. The latter has been used successfully in dedicated natural gas engines and dual fuel engines with a primary focusbeing to lower the operating costs. Meanwhile, there has been an increase in research focusing on the development of distributed micro-CHP systems that use natural gas as the fuel with a target of 1 kW of electrical (kWe) power.

Recent publications have demonstrated that efficient CHP systems and proper sizing of the heat-exchanging device relies heavily upon knowledge of the energy availability. Unfortunately, a thorough review of published data shows that significant data sets on gaseous fuel applications in micropower generation scales is lacking.

To this note, researchers at West Virginia University comprising of Dr. Mahdi Darzi, Dr. Derek Johnson, Chris Ulishney, and Dakota Oliver from Mechanical and Aerospace Engineering Department, Center for Alternative Fuels, Engines, and Emissions presented a study where they focused on addressing the aforementioned issue. Knowing that the missing data sets are essential for researchers and economists when it comes to analyzing the viability and cost effectiveness of new technologies, the researchers opted for a novel approach with the goal being to improve the 1st law efficiency through the use of low pressure direct injection (LPDI) in order to maximize mechanical work which could be used for electrical power generation. Their work is currently published in the research journal, Energy Conversion and Management.

In brief, their approach focused on examining the detailed energy and exergy distribution of a 34 cc (cc) air-cooled, two-stroke engine configured to operate on different natural gas (NG) compositions, pure methane, and propane. The engine was developed for application in a small, decentralized combined heat and power (CHP) system. It included optimized intake and exhaust resonators designed from Helmholtz resonance theory to promote effective scavenging. Generally, the team carried out full energy and exergy distribution analyses, as engine operating regimes changed. Exergy was divided into work (available), lost (recoverable), and destructed availabilities.

The authors reported that fuel loss and heat transfer contributed the most to exergy losses, accounting for around 15% and 9% of fuel exergy, respectively. Propane showed the highest in-cylinder trapped energy, heat transfer and, peak utilization factor (UF) of 85.3%. Due to fuel presence in the exhaust, lower 1st law efficiency did not necessarily result into a lower 2nd law efficiency.

In summary, a small two-stroke engine with 1–1.5 kW power output at 5400 RPM speed was operated with different gaseous fuels to examine their impact on energy and exergy distributions. Detailed 1st and 2nd law analyses were performed. On matters regarding fuel impacts, propane was seen to provide the highest power density and available heat for energy recovery – in both magnitude and quality. Altogether, their approach presents a practical analysis of heat recovery and power efficiency recovery for small NG engines that could power micro-CHP systems

Gaseous fuels variation effects on first and second law analyses of a small direct injection engine for micro-CHP systems - Advances in Engineering

Reference

Mahdi Darzi, Derek Johnson, Chris Ulishney, Dakota Oliver. Gaseous fuels variation effects on first and second law analyses of a small direct injection engine for micro-CHP systems. Energy Conversion and Management, volume 184 (2019) page 609–625.

Go To Energy Conversion and Management

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