如何在C中使用签名将文件输出为UTF8#

我试图在ASP中输出一个excel文件作为附件。NET,很难用土耳其语编码。以下代码是我所做的;我将我尝试过的行作为评论留下:

  var collection = Data.Get<Students>()
    .Where(t => t.Year == activeYear)
    .OrderBy(t => t.Name);

  var total = collection.Count();

  DataTable dt = collection.ToDataTable();
  dt.Columns.Remove("Id");

  string htmlCode = "<table>";

  //add header row
  htmlCode += "<tr>";
  htmlCode += "<td>#</td>";

  for (int i = 0; i < dt.Columns.Count; i++)
  {
      htmlCode += "<td>" + dt.Columns[i].ColumnName + "</td>";
  }

  htmlCode += "</tr>";

  //add rows
  for (int i = 0; i < dt.Rows.Count; i++)
  {
    htmlCode += "<tr>";
    htmlCode += "<td>" + (dt.Rows.Count-i+1).ToString() + "</td>";

    for (int j = 0; j < dt.Columns.Count; j++)
    {
        htmlCode += "<td>" + dt.Rows[i][j].ToString() + "</td>";
    }

    htmlCode += "</tr>";
  }

  htmlCode += "</table>";   


  ////////////////////////////////////
  // Encoding part begins here
  ////////////////////////////////////

  var output = htmlCode;

  Encoding encoding =  new UTF8Encoding(true); //Encoding.UTF8; //new UTF8Encoding(true);
  var utf8bytes = encoding.GetBytes(output);
  utf8bytes = Encoding.UTF8.GetPreamble().Concat(utf8bytes).ToArray();
  byte[] bytes = new UTF8Encoding(true).GetBytes(output);
  //MemoryStream stream = new MemoryStream(utf8bytes);
  MemoryStream stream = new MemoryStream(bytes);

  StreamReader reader = new StreamReader(stream);

  Response.Clear();
  Response.Buffer = true;
  Response.ClearContent();

  string attachment = "attachment; filename=" + Utils.Security.RemoveDiacritics(currentLesson + "-" + activeYear) + ".xls";
  Response.AddHeader("content-disposition", attachment);
  //Response.ContentType = "application/octet-stream";
  Response.ContentType = "application/vnd.ms-excel";

  Response.ContentEncoding = new UTF8Encoding(true); //Encoding.GetEncoding("windows-1254"); // Encoding.UTF8;
  Response.Output.Write(reader.ReadToEnd());
  Response.Flush();
  Response.End();

如果我使用新的UTF8Encoding(true)或false,输出总是不带签名的UTF8。如果我在Notepad2中打开文件,并将其编码为带有签名的UTF8,则名称将正确显示。

这是下载的Excel文件,Excel中的名称不正确:

这是Notepad2中修改后的Excel文件,其名称在Excel中显示正确:

为了更正名称,我使用Notepad2打开下载的xls文件,并使用Signature将编码从UTF8更改为UTF8。现在,我如何在服务器端做到这一点?

更新: HEX编辑器屏幕截图显示了文件之间的差异,只在xls平面文本文件的开头添加了3个字节: