The Hybrid Rich-Burn/Lean-Burn Engine

Abstract

This paper describes a new low-emissions engine concept called the hybrid rich-burn/lean-burn (HRBLB) engine. In this concept a portion of the cylinders of a multicylinder engine are fueled with a very rich natural gas-air mixture. The remaining cylinders are operated with a lean mixture of natural gas and air and supplemented with the rich combustion exhaust. The goal of this unique concept is the production of extremely low NOx (e.g., 5 ppm when corrected to 15 percent exhaust oxygen content). This is accomplished by operating outside the combustion limits where NOx is produced. In rich combustion an abundance of hydrogen and carbon monoxide is produced. Catalyst treatment of the rich exhaust can be employed to increase the hydrogen concentration and decrease the carbon monoxide concentration simultaneously. The hydrogen-enriched exhaust is used to supplement the lean mixture cylinders to extend the lean limit of combustion, and thus produces ultralow levels of NOx. Results to date have shown NOx levels as low as 8 ppm at 15 percent oxygen can be achieved with good combustion stability and thermal efficiency.

Estimating IC engine exhaust gas lambda and oxygen from the response of a universal exhaust gas oxygen sensor

“…This approximate form gives good estimates for 'normal' gases. For example, using the standard conditions stated at the beginning of the this section, equation (22) overestimates X O 2 by approximately 0.001 in the range 1 < λ < 5. At or near to λ = 1 such errors are significant, and the errors themselves are rather variable with fuel type and T equ .…”

“…In some circumstances equation ( 22) will be badly in error, even for lean gases. For example in [22] very rich gas is recirculated to the inlet manifold. A UEGO sensor placed in the mixed fresh air/recirculated gas stream could however, with the RM model, be used make estimates of the recirculation rate using the exhaust chemistry.…”

“…In the lean region, it is easy to show from simple chemistry that, almost independently of the fuel composition, q ≈ λ−1 λ , and this is confirmed using the FCM, as can be seen from figure 4. With reference to equation ( 7) though, it is not surprising that a slightly improved prediction can be obtained by using a second order fit: this has been found to be λ − 1 λ ≈ −0.22q 2 + 1.21q = s(q) (22) little affected by fuel composition or T equ .…”

Feasibility Study of Biogas Reforming To Improve Energy Efficiency and To Reduce Nitrogen Oxide Emissions

“…where ΔH R,j 298. 16 (kJ/mol) is the standard heat of reaction at reference conditions (298.16 K) and ΔC pj is described by…”

“…Another means to improve the energetics of hydrogen production during power generation is via the employment of combined heat and power (CHP) advanced cycle concepts that center around the idea of waste heat recovery in the engine exhaust. An interesting such concept, known as the chemical recuperation (CR) cycle, which is the focus of the present project, was first proposed in the late 1990s − and has been studied since. It involves the use of “waste heat” from the combustor exhaust to produce from NG, via catalytic reforming, a H 2 -rich syngas (SG) mixture (containing, in addition, CO, CO 2 and unreacted CH 4 ) which is then used for power generation.…”