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In this study, cyclic variations in dual fuel combustion with diesel ignition of three different low reactivity fuels (methane, propane, and gasoline) are examined under identical operating conditions. Experiments were performed on a single cylinder research engine (SCRE) at a low load of 3.3 bar brake mean effective pressure (BMEP). The start of injection (SOI) of diesel was varied from 280 to 330 absolute crank angle degrees (CAD). Engine speed, rail pressure, and boost pressure were held constant at 1500 rpm, 500 bar, and 1.5 bar, respectively. The energy substituted by the low reactivity fuel was fixed at 80% of the total energy input. It was found that diesel-methane (DM) and diesel-propane (DP) combustion were affected by diesel mixing to a greater extent than diesel-gasoline (DG) combustion due to the higher reactivity of gasoline. The magnitude of low temperature heat release was greatest for DG combustion followed by DM and DP combustion for all SOIs. The ignition delay for DG combustion was the shortest, followed by DM and DP combustion. DM and DP combustion exhibited more cyclic variations than DG combustion. Cyclic variations decreased for DM and DP combustion when SOI was advanced; however, DG combustion cyclic variations remained essentially constant for all SOIs. Earlier SOIs (280, 290, 300, and 310 CAD) for DM and (280, 290, and 300 CAD) for DP combustion indicated some prior-cycle effects on the combustion and IMEP (i.e. some level of determinism). [ABSTRACT FROM AUTHOR]

This work experimentally examines the effect of methane (a natural gas surrogate) substitution on early injection dual fuel combustion at representative low loads of 3.3 and 5.0 bar BMEPs in a single-cylinder compression ignition engine. Gaseous methane fumigated into the intake manifold at various methane energy fractions was ignited using a high-pressure diesel pilot injection at 310 °CA. For the 3.3 bar BMEP, methane energy fraction sweeps from 50% to 90% were performed; while at 5.0 bar BMEP, methane energy fraction sweeps from 70% to 90% were performed. It is observed that minimum methane energy fraction is limited by maximum pressure rise rate leading to knock and maximum methane energy fraction is limited by a high coefficient of variation in netIMEP, which leads to high cyclic variations. For 3.3 bar BMEP, maximum pressure rise rate is 8 bar/°CA at 50% methane energy fraction while at 5 bar BMEP, it is 12 bar/°CA at 70% methane energy fraction. For 3.3 bar BMEP, engine-out NOx emissions decrease by 43 times when methane energy fraction increases from 50% to 90%, and it decreases by nearly 46 times when methane energy fraction increases from 70% to 90% at 5 bar BMEP. Engine-out unburned hydrocarbon emissions increase by nearly 9 times when methane energy fraction increases from 50% to 90% at 3.3 bar BMEP, and it increases by nearly 5 times when methane energy fraction increases from 70% to 90% at 5.0 bar BMEP. Engine-out carbon monoxide emissions increase by nearly 7 times when methane energy fraction increases from 50% to 90% at 3.3 bar BMEP and by nearly 5 times when methane energy fraction increases from 70% to 90% at 5.0 bar BMEP. In addition, cyclic combustion variations at both loads were analyzed to obtain further insights into the combustion process and identify opportunities to further improve fuel conversion efficiencies at low load operation. [ABSTRACT FROM AUTHOR]

While dual fuel low temperature combustion (LTC) has been studied before, a detailed second law analysis of dual fuel LTC is not yet available in the open literature. To address this gap, a previously validated, closed-cycle, multi-zone, simulation of diesel-natural gas dual fuel LTC was used to perform a second law analysis. For the present study, a 2.4-l single-cylinder research engine operating at a nominal load of 6 bar BMEP and 1700 rpm was used. Zone-wise thermodynamic irreversibilities as well as total cumulative entropy generated and lost available work over the closed cycle were quantified. Subsequently, two convenient second-law parameters were defined: (1) the “lost available indicated mean effective pressure” (LAIMEP), which can be interpreted as an engine-size-normalized measure of available work that is lost due to thermodynamic irreversibilities (analogous to the relationship between indicated mean effective pressure and indicated work); (2) fuel conversion irreversibility (FCI), which is defined as the ratio of lost available work to total fuel chemical energy input. Finally, parametric studies were performed to quantify the effects of diesel start of injection, intake manifold temperature, and intake boost pressure on LAIMEP and FCI. The results show that significant entropy generation occurred in the flame zone (52–61 percent) and the burned zone (31–39 percent) while packets account for less than 6 percent of the overall irreversibilities. Parametric studies showed LAIMEPs in the range of 645–768 kPa and FCIs in the range of 32.8–39.2 percent at different engine operating conditions. Although the present study focused on dual fuel LTC, the conceptual definitions of LAIMEP and FCI are generally applicable for comparing the thermodynamic irreversibilities of IC engines of any size and operating on any combustion strategy. [ABSTRACT FROM AUTHOR]

• Demonstrated rigorous exergy analysis methodology for IC engine applications. • Computed crank-resolved exergy components for dual fuel low temperature combustion. • Characterized diesel injection timing effects on in-cylinder exergy distributions. • Defined and quantified engine exergetic efficiencies, accounting for exhaust exergy. Increasing fuel efficiency of internal combustion (IC) engines is an imperative economic and environmental need. To this end, in the present work, an exergy analysis methodology was developed and incorporated within a previously validated, closed cycle, multi-zone, thermodynamic simulation of diesel-methane dual fuel low temperature combustion (LTC). To study in-cylinder exergy transformation, the diesel start of injection (SOI) was varied from 300 crank angle degrees (CAD) to 340 CAD for a fixed engine load 6 bar brake mean effective pressure (BMEP) and speed (1700 rev/min). Gross indicated fuel conversion efficiency (iFCE) and exergetic efficiency (including exhaust exergy at exhaust valve opening) were computed for different SOIs. Results show that at all SOIs ~41–42 percent of the total input exergy was destroyed due to combustion irreversibilities. When combustion started, in-cylinder chemical exergy reduced significantly due to exergy transfers associated with work transfer and heat transfer as well as exergy destruction. While at SOI = 340 CAD (representative of conventional dual fuel combustion), ~14 percent of the fuel chemical exergy exited as exhaust physical exergy, this reduced to ~5.5 percent at SOI = 300 CAD (representative of dual fuel LTC). The "maximum efficiency SOI" was SOI = 310 CAD with an iFCE of 43.6 percent and an exergetic efficiency of 52.2 percent. [ABSTRACT FROM AUTHOR]

Dual fuel low temperature combustion (LTC) strategies are attractive for future internal combustion engines due to their promise of very low engine-out emissions of oxides of nitrogen (NO x ) and particulate matter. In the present work, experimental results for diesel-ignited methane dual fuel LTC on a compression ignition single cylinder research engine (SCRE) are presented. Methane was fumigated into the intake manifold and diesel injection was used to initiate combustion. The engine was operated at a constant speed of 1500 rev/min, and diesel injection pressure was fixed at 500 bar. The start of injection (SOI) of diesel fuel was varied from 260° to 360° (i.e., TDC) to quantify its impact on engine performance and engine-out, indicated-specific emissions of NO x (ISNO x ), carbon monoxide (ISCO), and unburned hydrocarbons (ISHC), and smoke emissions. The SOI sweeps were performed at different net indicated mean effective pressures (IMEPs) of 4.1 and 12.1 bar. Intake manifold pressure and methane percent energy substitution (PES) were fixed at 1.5 bar and 80%, respectively, for 4.1 bar IMEP and at 1.8 bar and 95%, respectively, for 12.1 bar IMEP. For all loads, when SOI was advanced, the longer ignition delays caused the separation between the fuel injection and the combustion events to increase. This was accompanied by a change in the shape of the AHRR curve from a distinct two-stage profile to a smooth, single-stage (almost Gaussian) profile. Advancing SOI to 300° and beyond yielded minimal engine-out ISNO x emissions (∼0.15 g/kW h at 4.1 bar IMEP and ∼1.3–1.5 g/kW h at 12.1 bar IMEP). Smoke emissions were negligible (<0.05 FSN) for all loads and all SOIs. Very high ISHC and ISCO emissions were observed for near-TDC SOI at all loads. The lowest ISHC and ISCO levels occurred for SOIs near 310° and for more advanced SOIs, both emissions increased. High pressure rise rates and the tendency to knock prevented engine operation at intermediate SOIs between 310° and 340° for 12.1 bar IMEP. On the other hand, for both 4.1 bar and 12. 1 bar IMEPs, high coefficient of variation of IMEP (>5%) caused unstable engine operation for SOIs advanced beyond 280°. [ABSTRACT FROM AUTHOR]