Method of detecting start of combustion in diesel engines using in-cylinder pressure

Abstract

Disclosed herein is a method of estimating the start of combustion (SOC) in a diesel engine using a difference between an in-cylinder combustion pressure and a motoring pressure so as to effectively control the combustion in a combustion chamber. The method of the present invention features that it comprises the steps of: detecting a DP value defined as a difference pressure between an in-cylinder combustion pressure and a motoring pressure; detecting a crank angle (CADPxx) at a point where the detected DP value equals a specific pressure; defining an angle difference between the start of combustion (SOC) and the crank angle (CADPxx) as a detected delay angle (ΔCADD) and determining the detected delay angle (ΔCADD) through an experiment of measuring the start of combustion (SOC) and the crank angle (CADPxx); and detecting the SOC using the following Equation: SOC=CADPxx−ΔCADD, whereby the SOC can be estimated simply and accurately, and that the detected delay angle (ΔCADD) is defined as a simple function for the engine speed.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, features and advantages of the present invention will be apparent from the following detailed description of the preferred embodiments of the invention in conjunction with the accompanying drawings, in which:

FIG. 1 is a graph illustrating a change in injection command, injection rate and rate of heat release (ROHR) in a combustion chamber over time in a diesel engine according to the prior art.

FIG. 2 is a graph illustrating the relationship between a variation of the SOC and the amount of NOx/HC emissions of a diesel engine.

FIG. 3 is a diagrammatic graph illustrating a method of detecting the SOC according to the present invention;

FIG. 4 is a graph illustrating the relationship between the SOC and the CA_DP10 at 1500 rpms;

FIG. 5 is a graph illustrating the relationship between the SOC and the CA_DP10 at 2000 rpms;

FIG. 6 is a graph illustrating the relationship between the SOC and the CA_DP10 at 2500 rpms;

FIG. 7 is a graph illustrating the relationship between the SOC and the CA_DP10 at 3000 rpms;

FIG. 8 is a graph illustrating a variation in a detected delay angle (ΔCA_DD) according to a change in an engine speed (rpm); and

FIG. 9 is a graph illustrating the detected delay angle (ΔCA_DD) with respect to 150 different operating conditions (injection time, SOE, and common rail pressure change) at 2000 rpms.

Claims

1. A method of detecting a start of combustion (SOC) in a diesel engine using an in-cylinder pressure, comprising the steps of: i) detecting a DP value defined as a difference pressure between an in-cylinder combustion pressure and a motoring pressure;ii) detecting a crank angle (CADPxx) at a point where the detected DP value is a specific pressure;iii) defining an angle difference between the start of combustion (SOC) and the crank angle (CADPxx) as a detected delay angle (ΔCADD) and determining the detected delay angle (ΔCADD) through an experiment of measuring the start of combustion (SOC) and the crank angle (CADPxx); andiv) detecting the SOC using the following Equation: SOC=CADPxx−ΔCADD.

2. The method as set forth in claim 1, wherein the detected delay angle (ΔCADD) is defined as the following Equation: ΔCADD(N)=k0N2+k1N+k2 where N is the revolution per minute of the engine, and k0, k1, and k2 are arbitrary numbers for representing the relationship between N and ΔCADD.