Experiments and zero D modeling studies using specific Wiebe coefficients for producer gas as fuel in spark-ignited engines

Abstract

The paper addresses experiments and modeling studies on the use of producer gas, a bio-derived low energy content fuel in a spark-ignited engine. Producer gas, generated in situ, has thermo-physical properties different from those of fossil fuel(s). Experiments on naturally aspirated and turbo-charged engine operation and subsequent analysis of the cylinder pressure traces reveal significant differences in the heat release pattern within the cylinder compared with a typical fossil fuel. The heat release patterns for gasoline and producer gas compare well in the initial 50% but beyond this, producer gas combustion tends to be sluggish leading to an overall increase in the combustion duration. This is rather unexpected considering that producer gas with nearly 20% hydrogen has higher flame speeds than gasoline. The influence of hydrogen on the initial flame kernel development period and the combustion duration and hence on the overall heat release pattern is addressed. The significant deviations in the heat release profiles between conventional fuels and producer gas necessitates the estimation of producer gas-specific Wiebe coefficients. The experimental heat release profiles are used for estimating the Wiebe coefficients. Experimental evidence of lower fuel conversion efficiency based on the chemical and thermal analysis of the engine exhaust gas is used to arrive at the Wiebe coefficients. The efficiency factor a is found to be 2.4 while the shape factor m is estimated at 0.7 for 2% to 90% burn duration. The standard Wiebe coefficients for conventional fuels and fuel-specific coefficients for producer gas are used in a zero D model to predict the performance of a 6-cylinder gas engine under naturally aspirated and turbo-charged conditions. While simulation results with standard Wiebe coefficients result in excessive deviations from the experimental results, excellent match is observed when producer gas-specific coefficients are used. Predictions using the same coefficients on a 3-cylinder gas engine having different geometry and compression ratio(s) indicate close match with the experimental traces highlighting the versatility of the coefficients.

Influence of fuel hydrogen fraction on syngas fueled SI engine: Fuel thermo-physical property analysis and in-cylinder experimental investigations

“…With PG having higher reference burning velocity as compared to NG, the increase in combustion duration can only be attributed to the reduced flame speed due to cooling of the mixture [24]. The interpretation is further corroborated by the fact that the exhaust gas temperature for PG fueled operation was about 75 K higher as compared to NG exhaust gas temperature [26,29,30] (higher exhaust gas temperature is indicative of late burning [21]). The inset data in Fig.…”

“…Literature reports the position of peak pressure for conventional fuels to be in the vicinity of 15 after TDC [21,65]. In working with PG, the authors have observed the MBT ignition timing around 13 after TDC [26,28]. In the current investigation, starting with composition C1 and following on the previous experience, the ignition timing was first adjusted to have the position of peak pressure based on the 50 cycle ensemble average pressure profile between 12 and 15 after the TDC.…”

“…Sample calculation for composition C1 is presented below. The value 4.65 kWe/l is based on previous operational experience on naturally aspirated engines [26,30,66] Addressing the MBT ignition timing, mixture H 2 fraction increase demands retarding the ignition setting, attributed to the increase in the laminar flame speed (refer Fig. 5) and dictated by the need for positioning the combustion phasing to maximize thermal to mechanical energy conversion.…”

Hydrogen-natural gas combustion in a marine lean-burn SI engine: A comparitive analysis of Seiliger and double Wiebe function-based zero–dimensional modelling

“…[33] used values of 2.8 and 2.4 for the combustion efficiency and shape factor in a single Wiebe function to study the influence of hydrogen-methane blends on the knock occurrence crank angle (KOCA) in a 2kW Cooperative Fuel Research (CRF) Engine. Shivapuji and Dasappa [54] used a single Wiebe function to model the combustion of producer gas in a 28 kWe SI engine and showed that the Wiebe coefficients need to be adapted to capture the in-cylinder pressure variations. Furthermore, Carrera et.…”

A two-zone reaction-based combustion model for a spark-ignition engine

“…Rakopoulos and colleagues 2,10 proposed a multi-zone combustion model for engine transient performance and NOx (nitric-oxide) formation of a syngas SI engine. However, the MFB rate of these discussed two- and multi-zone models 5–14 is generated by an empirical Wiebe function that needs to be calibrated as a function of engine speed, load, and exhaust-gas-recirculation (EGR) for each engine operating condition.…”