Steady-State biodiesel blend estimation via a wideband oxygen sensor

Abstract

A substantial opportunity exists to reduce carbon dioxide (CO2) emissions as well as dependence on foreign oil by developing strategies to cleanly and efficiently use biodiesel, a renewable, domestically available, alternative diesel fuel. However, biodiesel utilization presents several challenges, including decreased fuel energy density and increased emissions of smog-generating nitrogen oxides (NOx). These negative aspects can likely be mitigated via closed-loop combustion control provided the properties of the fuel blend can be estimated accurately, on-vehicle, in real-time. To this end, this paper presents a method to practically estimate the biodiesel content of fuel being used in a diesel engine during steady-state operation. The simple, generalizable, physically motivated estimation strategy presented utilizes information from a wideband oxygen sensor in the engine's exhaust stream, coupled with knowledge of the air-fuel ratio, to estimate the biodiesel content of the fuel. Experimental validation was performed on a 2007 Cummins 6.7 liter ISB series engine. Four fuel blends (0%, 20%, 50% and 100% biodiesel) were tested at a wide variety of torque-speed conditions. The estimation strategy correctly estimated the biodiesel content of the four fuel blends to within 4.2% of the true biodiesel content. Blends of 0%, 20%, 50% and 100% were estimated to be 2.5%, 17.1%, 54.2%, and 96.8% respectively. The results indicate that the estimation strategy presented is capable of accurately estimating the biodiesel content in a diesel engine during steady-state engine operation. This method offers a practical alternative to in-the-fuel type sensors, because wideband oxygen sensors are already in widespread production and are in place on some modern diesel vehicles today.

Excess Air Ratio Management in a Diesel Engine with Exhaust Backpressure Compensation

“…This section benchmarks the wideband lambda sensor model proposed in Equation ( 8) against other correlations available in the literature. Model 1 refers to the correlation by Irimescu [17] expressed directly through Equation (5). Model 2 refers to the approach by Bosch [25], where the sensor characteristics from Figure 2 were used to convert the pump current expressed by Equation (4) to the λ app values.…”

“…Furthermore, in lean-burn marine gas engines, the absolute λ signal can be used for virtual knock estimation. This wide spectrum of UEGO sensor applications is complemented by virtual λ-based fuel composition sensing for gasoline-ethanol [4] or diesel-FAME (fatty acid methyl ester) [5] flex-fuel engines.…”

“…The type of fuel may affect oxygen sensor readings. The effect is straightforward for oxygenated fuels and enables on-board FAME admixture estimation [5]. The Bosch (Robert Bosch GmbH, Stuttgart, Germany) R&D group reported significant differences between the readings of their sensors for gasoline and ethanol [4].…”

Closed-loop combustion control of biodiesel–diesel blends in premixed operating conditions enabled via high exhaust gas recirculation rates

“…The biodiesel blend estimation technique utilized for these tests is based on the fact that the exhaust oxygen fractions for diesel and biodiesel differ at the same mixture fraction owing to oxygenation of biodiesel. 32 A dynamic blend estimation technique with an extended Kalman filter as detailed by Snyder et al 33 was used for estimation of the biodiesel blend in this work.…”

Energy-based and oxygen-based biodiesel blend level estimation methods for diesel engines

“…In [8], Synder et al pointed out that biodiesel is oxygenated but conventional diesel is not and this difference can be detected by utilizing a wideband oxygen sensor. This method was proven to be effective through their experiments.…”