**2. Experimental setup and tests**

Measurements were carried out on a two‐cylinder diesel engine equipped with a common rail injection system, whose main application is in micro cars and urban vehicles (its technical data are reported in **Table 1**).


**Table 1.** Engine specifications.

Two configurations of the engine have been tested: naturally aspirated and turbocharged.

The engine was installed with an asynchronous motor (Siemens 1PH7, characterized by nominal torque 360 Nm and power 70 kW) in the test bed of Engineering Department at Roma Tre University. The engine was managed by a fully opened ECU, in order to control injection parameters (injection strategy, injection timing, and duration).

HBM T12 was used for torque measurement. AVL Fuel Balance 733 was used for fuel consumption measurement.

Data acquisition was controlled by means of LabVIEW software, by using self‐developed pro-

Remote Combustion Sensing in Diesel Engine via Vibration Measurements

http://dx.doi.org/10.5772/intechopen.69761

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The measurements were performed over the engine speed range 2000–4400 rpm, at different load conditions (from 50% to full load condition). For each running condition, 25 engine cycles were used to average the signal, thus to attenuate the engine cycle irregularities; the

All acquisitions started after the engine warm‐up, when the engines reached under nominally

This section focuses on the vibration and in‐cylinder pressure data processing and it is devoted to describe in detail the developed methodology. In the first part, some representative crank angle evolutions of in‐cylinder pressure and accelerometer signals related to naturally aspired configuration are shown and results of frequency domain analysis are presented. In the sec-

**Figures 2**–**5** present the time‐histories related to naturally aspirated configuration of the engine. The plot of **Figure 2** shows data obtained at 2000 rpm, full load condition with three different injection settings, according to **Table 2**. Case 1 was characterized by two‐shot injections (pre and main injections). In cases 2 and 3, multiple injections (pilot, pre, and main injec-

ond part, results obtained with the turbocharged engine configuration are shown.

tions) were imposed. These cases differentiate for the injection timings.

grams. NI board types 6110, 6533, and 6259 were used.

**Figure 1.** (a) Engine set up; (b) accelerometer location.

DATA ACQUISITION

SIGNAL CONDITIONING

IN-CYLINDER PRESSURE TRANSDUCERS

(a) (b)

ANGLE ENCODER

ACCELEROMETER

stationary conditions.

**3. Results**

increase of such a number did not change the feature of the trends.

The in‐cylinder pressure was measured with a piezoelectric transducer AVL GU13P (the preheating plug was substituted by the pressure probe).

The engine speed and the crank angle position were measured by the optical encoder AVL 364C. It generates transistor‐transistor logic (TTL) rectangular pulse signals: one is the trigger signal that was used to compute the engine speed; the other is the code division multiplexing (CDM) signal that was set to a resolution of 0.1 crank angle degrees.

An Endevco 7240C accelerometer was used to measure the engine block vibration. It is a high‐temperature piezoelectric mono‐axial accelerometer with a nominal sensitivity of 3 pC/g and a resonance frequency of 90 kHz. The vibration signal was conditioned via B&K Nexus device (amplifier and low‐pass filter). A preliminary investigation was devoted to select the optimal position and orientation of the accelerometer, able to guarantee high sensitivity as regards the combustion event and low sensitivity to mechanical sources. Details may be found in Ref. [18]. The accelerometer was mounted on the top of the engine block by means of a threaded pin on one of the stud that fastens the cylinder head to the block. The mounting was chosen in order to ensure a rigid connection to the structural engine members.

**Figure 1** shows the engine setup and a detail of the accelerometer location.

The sampling frequency was varied according to the engine speed, thus to ensure a fixed crank angle resolution of the signals.

**Figure 1.** (a) Engine set up; (b) accelerometer location.

Data acquisition was controlled by means of LabVIEW software, by using self‐developed programs. NI board types 6110, 6533, and 6259 were used.

The measurements were performed over the engine speed range 2000–4400 rpm, at different load conditions (from 50% to full load condition). For each running condition, 25 engine cycles were used to average the signal, thus to attenuate the engine cycle irregularities; the increase of such a number did not change the feature of the trends.

All acquisitions started after the engine warm‐up, when the engines reached under nominally stationary conditions.
