Exhaust valve profile modulation for improved diesel engine curb idle aftertreatment thermal management

Abstract

Rapid warm-up of a diesel engine aftertreatment system (ATS) is a challenge at low loads. Modulating exhaust manifold pressure (EMP) to increase engine pumping work, fuel consumption, and as a result, engine-outlet temperature, is a commonly used technique for ATS thermal management at low loads. This paper introduces exhaust valve profile modulation as a technique to increase engine-outlet temperature for ATS thermal management, without requiring modulation of exhaust manifold pressure. Experimental steady state results at 800 RPM/1.3 bar BMEP (curb idle) demonstrate that early exhaust valve opening with negative valve overlap (EEVO+NVO) can achieve engine-outlet temperature in excess of 255°C with 5.7% lower fuel consumption, 12% lower engine out NOx and 20% lower engine-out soot than the conventional thermal management strategy. Late exhaust valve opening with internal EGR via reinduction (LEVO+Reinduction) resulted in engine-outlet temperature in excess of 280°C, while meeting emission constraints at no fuel consumption penalty. This work also demonstrates that LEVO in conjunction with modulation of exhaust manifold pressure results in engine-outlet temperature in excess of 340°C while satisfying desired emission constraints. Aggressive use of LEVO can result in engine-outlet temperatures of 460°C, capable of active regeneration of DPF at curb idle, without the significant increase in engine-out soot emissions seen in previously studied strategies.

Diesel Engine 2-Stroke Breathing for Aftertreatment Warm-Up

“…Also included are results from work done by Joshi 21 using LEVO. These results provide an interesting point of comparison, as while they have the same objective (faster warm-up of the SCR) and employ the same VVA engine, they use a completely different approach.…”

“…Joshi et al 21 employed late exhaust valve opening (LEVO), which provided similar benefits to EEVO through recompressing the exhaust gas before exhausting (and thereby increasing the temperature) and by throttling the exhaust valve, both of which require additional fuel consumption, producing higher temperatures. Engine-out exhaust temperatures of almost 350°C where demonstrated without an increase in emissions relative to baseline.…”

A method to quantify the advantages of a variable valve train for CI engines

“…Most of the strategies mentioned increase the engineout enthalpy at the expense of increased fuel consumption. 3,6,7,[17][18][19][20][21][22][23] Alternatively, various cylinder deactivation strategies can also be used to increase exhaust enthalpy. 7,8,[24][25][26][27][28] In comparison to the valve timing strategies mentioned, cylinder deactivation results in a higher engine-out temperature, but it also lowers engine mass flow and is therefore better suited for stay-warm operation.…”

Effect of internal exhaust gas recirculation on performance, combustion, and emissions in a PFI camless engine

“…Authors also performed experiments by early exhaust valve opening with negative F I G U R E 1 Gas exchange process of SI engine valve overlap and found that a 5.7% lower fuel consumption, 12% lower engine out NO x and 20% lower engine out soot can be achieved. 13 The effect of NVO and PVO on performance improvements in homogeneous charge compression ignition (HCCI), controlled autoignition (CAI), and spark assisted compression ignition (SACI) engines have also been presented. [14][15][16][17][18][19][20][21][22] Ebrahimi et al 23 investigated the effect of symmetric NVO on energy and exergy distribution in a single cylinder port fuel injection (PFI) HCCI engine, which is equipped with an electromagnetic VVT system.…”

“…The effect of internal EGR achieved through NVO in a diesel engine has been investigated by Joshi et al 12 It has been reported that at low loads (800 rpm and 1.3 bar BMEP), introducing internal EGR, a 70% lower NO x , 35% lower fuel consumption, and 40% lower exhaust flow rate were achieved. Authors also performed experiments by early exhaust valve opening with negative valve overlap and found that a 5.7% lower fuel consumption, 12% lower engine out NO x and 20% lower engine out soot can be achieved 13 …”